use std::collections::HashMap;
use std::num::NonZeroUsize;
use std::os::fd::RawFd;
use std::sync::atomic::AtomicU64;
use std::sync::{Arc, Mutex};
use std::time::{Duration, Instant};

use enum_map::{Enum as _, EnumMap};
use futures::Future;
use metrics::{
    Counter, CounterVec, GaugeVec, Histogram, HistogramVec, IntCounter, IntCounterPair,
    IntCounterPairVec, IntCounterVec, IntGauge, IntGaugeVec, UIntGauge, UIntGaugeVec,
    register_counter_vec, register_gauge_vec, register_histogram, register_histogram_vec,
    register_int_counter, register_int_counter_pair_vec, register_int_counter_vec,
    register_int_gauge, register_int_gauge_vec, register_uint_gauge, register_uint_gauge_vec,
};
use once_cell::sync::Lazy;
use pageserver_api::config::{
    PageServicePipeliningConfig, PageServicePipeliningConfigPipelined,
    PageServiceProtocolPipelinedBatchingStrategy, PageServiceProtocolPipelinedExecutionStrategy,
};
use pageserver_api::models::InMemoryLayerInfo;
use pageserver_api::shard::TenantShardId;
use postgres_backend::{QueryError, is_expected_io_error};
use pq_proto::framed::ConnectionError;
use strum::{EnumCount, IntoEnumIterator as _, VariantNames};
use strum_macros::{IntoStaticStr, VariantNames};
use utils::id::TimelineId;

use crate::config;
use crate::config::PageServerConf;
use crate::context::{PageContentKind, RequestContext};
use crate::pgdatadir_mapping::DatadirModificationStats;
use crate::task_mgr::TaskKind;
use crate::tenant::Timeline;
use crate::tenant::layer_map::LayerMap;
use crate::tenant::mgr::TenantSlot;
use crate::tenant::storage_layer::{InMemoryLayer, PersistentLayerDesc};
use crate::tenant::tasks::BackgroundLoopKind;
use crate::tenant::throttle::ThrottleResult;

/// Prometheus histogram buckets (in seconds) for operations in the critical
/// path. In other words, operations that directly affect that latency of user
/// queries.
///
/// The buckets capture the majority of latencies in the microsecond and
/// millisecond range but also extend far enough up to distinguish "bad" from
/// "really bad".
const CRITICAL_OP_BUCKETS: &[f64] = &[
    0.000_001, 0.000_010, 0.000_100, // 1 us, 10 us, 100 us
    0.001_000, 0.010_000, 0.100_000, // 1 ms, 10 ms, 100 ms
    1.0, 10.0, 100.0, // 1 s, 10 s, 100 s
];

// Metrics collected on operations on the storage repository.
#[derive(Debug, VariantNames, IntoStaticStr)]
#[strum(serialize_all = "kebab_case")]
pub(crate) enum StorageTimeOperation {
    #[strum(serialize = "layer flush")]
    LayerFlush,

    #[strum(serialize = "layer flush delay")]
    LayerFlushDelay,

    #[strum(serialize = "compact")]
    Compact,

    #[strum(serialize = "create images")]
    CreateImages,

    #[strum(serialize = "logical size")]
    LogicalSize,

    #[strum(serialize = "imitate logical size")]
    ImitateLogicalSize,

    #[strum(serialize = "load layer map")]
    LoadLayerMap,

    #[strum(serialize = "gc")]
    Gc,

    #[strum(serialize = "find gc cutoffs")]
    FindGcCutoffs,
}

pub(crate) static STORAGE_TIME_SUM_PER_TIMELINE: Lazy<CounterVec> = Lazy::new(|| {
    register_counter_vec!(
        "pageserver_storage_operations_seconds_sum",
        "Total time spent on storage operations with operation, tenant and timeline dimensions",
        &["operation", "tenant_id", "shard_id", "timeline_id"],
    )
    .expect("failed to define a metric")
});

pub(crate) static STORAGE_TIME_COUNT_PER_TIMELINE: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_storage_operations_seconds_count",
        "Count of storage operations with operation, tenant and timeline dimensions",
        &["operation", "tenant_id", "shard_id", "timeline_id"],
    )
    .expect("failed to define a metric")
});

// Buckets for background operation duration in seconds, like compaction, GC, size calculation.
const STORAGE_OP_BUCKETS: &[f64] = &[0.010, 0.100, 1.0, 10.0, 100.0, 1000.0];

pub(crate) static STORAGE_TIME_GLOBAL: Lazy<HistogramVec> = Lazy::new(|| {
    register_histogram_vec!(
        "pageserver_storage_operations_seconds_global",
        "Time spent on storage operations",
        &["operation"],
        STORAGE_OP_BUCKETS.into(),
    )
    .expect("failed to define a metric")
});

/// Measures layers visited per read (i.e. read amplification).
///
/// NB: for a batch, we count all visited layers towards each read. While the cost of layer visits
/// are amortized across the batch, and some layers may not intersect with a given key, each visited
/// layer contributes directly to the observed latency for every read in the batch, which is what we
/// care about.
pub(crate) static LAYERS_PER_READ: Lazy<HistogramVec> = Lazy::new(|| {
    register_histogram_vec!(
        "pageserver_layers_per_read",
        "Layers visited to serve a single read (read amplification). In a batch, all visited layers count towards every read.",
        &["tenant_id", "shard_id", "timeline_id"],
        // Low resolution to reduce cardinality.
        vec![4.0, 8.0, 16.0, 32.0, 64.0, 128.0, 256.0],
    )
    .expect("failed to define a metric")
});

pub(crate) static LAYERS_PER_READ_GLOBAL: Lazy<Histogram> = Lazy::new(|| {
    register_histogram!(
        "pageserver_layers_per_read_global",
        "Layers visited to serve a single read (read amplification). In a batch, all visited layers count towards every read.",
        vec![1.0, 2.0, 4.0, 8.0, 16.0, 32.0, 64.0, 128.0, 256.0, 512.0, 1024.0],
    )
    .expect("failed to define a metric")
});

pub(crate) static LAYERS_PER_READ_BATCH_GLOBAL: Lazy<Histogram> = Lazy::new(|| {
    register_histogram!(
        "pageserver_layers_per_read_batch_global",
        "Layers visited to serve a single read batch (read amplification), regardless of number of reads.",
        vec![
            1.0, 2.0, 4.0, 8.0, 16.0, 32.0, 64.0, 128.0, 256.0, 512.0, 1024.0
        ],
    )
    .expect("failed to define a metric")
});

pub(crate) static LAYERS_PER_READ_AMORTIZED_GLOBAL: Lazy<Histogram> = Lazy::new(|| {
    register_histogram!(
        "pageserver_layers_per_read_amortized_global",
        "Layers visited to serve a single read (read amplification). Amortized across a batch: \
            all visited layers are divided by number of reads.",
        vec![
            1.0, 2.0, 4.0, 8.0, 16.0, 32.0, 64.0, 128.0, 256.0, 512.0, 1024.0
        ],
    )
    .expect("failed to define a metric")
});

pub(crate) static DELTAS_PER_READ_GLOBAL: Lazy<Histogram> = Lazy::new(|| {
    // We expect this to be low because of Postgres checkpoints. Let's see if that holds.
    register_histogram!(
        "pageserver_deltas_per_read_global",
        "Number of delta pages applied to image page per read",
        vec![0.0, 1.0, 2.0, 4.0, 8.0, 16.0, 32.0, 64.0, 128.0, 256.0],
    )
    .expect("failed to define a metric")
});

pub(crate) static CONCURRENT_INITDBS: Lazy<UIntGauge> = Lazy::new(|| {
    register_uint_gauge!(
        "pageserver_concurrent_initdb",
        "Number of initdb processes running"
    )
    .expect("failed to define a metric")
});

pub(crate) static INITDB_SEMAPHORE_ACQUISITION_TIME: Lazy<Histogram> = Lazy::new(|| {
    register_histogram!(
        "pageserver_initdb_semaphore_seconds_global",
        "Time spent getting a permit from the global initdb semaphore",
        STORAGE_OP_BUCKETS.into()
    )
    .expect("failed to define metric")
});

pub(crate) static INITDB_RUN_TIME: Lazy<Histogram> = Lazy::new(|| {
    register_histogram!(
        "pageserver_initdb_seconds_global",
        "Time spent performing initdb",
        STORAGE_OP_BUCKETS.into()
    )
    .expect("failed to define metric")
});

pub(crate) struct GetVectoredLatency {
    map: EnumMap<TaskKind, Option<Histogram>>,
}

#[allow(dead_code)]
pub(crate) struct ScanLatency {
    map: EnumMap<TaskKind, Option<Histogram>>,
}

impl GetVectoredLatency {
    // Only these task types perform vectored gets. Filter all other tasks out to reduce total
    // cardinality of the metric.
    const TRACKED_TASK_KINDS: [TaskKind; 2] = [TaskKind::Compaction, TaskKind::PageRequestHandler];

    pub(crate) fn for_task_kind(&self, task_kind: TaskKind) -> Option<&Histogram> {
        self.map[task_kind].as_ref()
    }
}

impl ScanLatency {
    // Only these task types perform vectored gets. Filter all other tasks out to reduce total
    // cardinality of the metric.
    const TRACKED_TASK_KINDS: [TaskKind; 1] = [TaskKind::PageRequestHandler];

    pub(crate) fn for_task_kind(&self, task_kind: TaskKind) -> Option<&Histogram> {
        self.map[task_kind].as_ref()
    }
}

pub(crate) struct ScanLatencyOngoingRecording<'a> {
    parent: &'a Histogram,
    start: std::time::Instant,
}

impl<'a> ScanLatencyOngoingRecording<'a> {
    pub(crate) fn start_recording(parent: &'a Histogram) -> ScanLatencyOngoingRecording<'a> {
        let start = Instant::now();
        ScanLatencyOngoingRecording { parent, start }
    }

    pub(crate) fn observe(self) {
        let elapsed = self.start.elapsed();
        self.parent.observe(elapsed.as_secs_f64());
    }
}

pub(crate) static GET_VECTORED_LATENCY: Lazy<GetVectoredLatency> = Lazy::new(|| {
    let inner = register_histogram_vec!(
        "pageserver_get_vectored_seconds",
        "Time spent in get_vectored.",
        &["task_kind"],
        CRITICAL_OP_BUCKETS.into(),
    )
    .expect("failed to define a metric");

    GetVectoredLatency {
        map: EnumMap::from_array(std::array::from_fn(|task_kind_idx| {
            let task_kind = TaskKind::from_usize(task_kind_idx);

            if GetVectoredLatency::TRACKED_TASK_KINDS.contains(&task_kind) {
                let task_kind = task_kind.into();
                Some(inner.with_label_values(&[task_kind]))
            } else {
                None
            }
        })),
    }
});

pub(crate) static SCAN_LATENCY: Lazy<ScanLatency> = Lazy::new(|| {
    let inner = register_histogram_vec!(
        "pageserver_scan_seconds",
        "Time spent in scan.",
        &["task_kind"],
        CRITICAL_OP_BUCKETS.into(),
    )
    .expect("failed to define a metric");

    ScanLatency {
        map: EnumMap::from_array(std::array::from_fn(|task_kind_idx| {
            let task_kind = TaskKind::from_usize(task_kind_idx);

            if ScanLatency::TRACKED_TASK_KINDS.contains(&task_kind) {
                let task_kind = task_kind.into();
                Some(inner.with_label_values(&[task_kind]))
            } else {
                None
            }
        })),
    }
});

pub(crate) struct PageCacheMetricsForTaskKind {
    pub read_accesses_immutable: IntCounter,
    pub read_hits_immutable: IntCounter,
}

pub(crate) struct PageCacheMetrics {
    map: EnumMap<TaskKind, EnumMap<PageContentKind, PageCacheMetricsForTaskKind>>,
}

static PAGE_CACHE_READ_HITS: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_page_cache_read_hits_total",
        "Number of read accesses to the page cache that hit",
        &["task_kind", "key_kind", "content_kind", "hit_kind"]
    )
    .expect("failed to define a metric")
});

static PAGE_CACHE_READ_ACCESSES: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_page_cache_read_accesses_total",
        "Number of read accesses to the page cache",
        &["task_kind", "key_kind", "content_kind"]
    )
    .expect("failed to define a metric")
});

pub(crate) static PAGE_CACHE: Lazy<PageCacheMetrics> = Lazy::new(|| PageCacheMetrics {
    map: EnumMap::from_array(std::array::from_fn(|task_kind| {
        let task_kind = TaskKind::from_usize(task_kind);
        let task_kind: &'static str = task_kind.into();
        EnumMap::from_array(std::array::from_fn(|content_kind| {
            let content_kind = PageContentKind::from_usize(content_kind);
            let content_kind: &'static str = content_kind.into();
            PageCacheMetricsForTaskKind {
                read_accesses_immutable: {
                    PAGE_CACHE_READ_ACCESSES
                        .get_metric_with_label_values(&[task_kind, "immutable", content_kind])
                        .unwrap()
                },

                read_hits_immutable: {
                    PAGE_CACHE_READ_HITS
                        .get_metric_with_label_values(&[task_kind, "immutable", content_kind, "-"])
                        .unwrap()
                },
            }
        }))
    })),
});

impl PageCacheMetrics {
    pub(crate) fn for_ctx(&self, ctx: &RequestContext) -> &PageCacheMetricsForTaskKind {
        &self.map[ctx.task_kind()][ctx.page_content_kind()]
    }
}

pub(crate) struct PageCacheSizeMetrics {
    pub max_bytes: UIntGauge,

    pub current_bytes_immutable: UIntGauge,
}

static PAGE_CACHE_SIZE_CURRENT_BYTES: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_page_cache_size_current_bytes",
        "Current size of the page cache in bytes, by key kind",
        &["key_kind"]
    )
    .expect("failed to define a metric")
});

pub(crate) static PAGE_CACHE_SIZE: Lazy<PageCacheSizeMetrics> =
    Lazy::new(|| PageCacheSizeMetrics {
        max_bytes: {
            register_uint_gauge!(
                "pageserver_page_cache_size_max_bytes",
                "Maximum size of the page cache in bytes"
            )
            .expect("failed to define a metric")
        },
        current_bytes_immutable: {
            PAGE_CACHE_SIZE_CURRENT_BYTES
                .get_metric_with_label_values(&["immutable"])
                .unwrap()
        },
    });

pub(crate) mod page_cache_eviction_metrics {
    use std::num::NonZeroUsize;

    use metrics::{IntCounter, IntCounterVec, register_int_counter_vec};
    use once_cell::sync::Lazy;

    #[derive(Clone, Copy)]
    pub(crate) enum Outcome {
        FoundSlotUnused { iters: NonZeroUsize },
        FoundSlotEvicted { iters: NonZeroUsize },
        ItersExceeded { iters: NonZeroUsize },
    }

    static ITERS_TOTAL_VEC: Lazy<IntCounterVec> = Lazy::new(|| {
        register_int_counter_vec!(
            "pageserver_page_cache_find_victim_iters_total",
            "Counter for the number of iterations in the find_victim loop",
            &["outcome"],
        )
        .expect("failed to define a metric")
    });

    static CALLS_VEC: Lazy<IntCounterVec> = Lazy::new(|| {
        register_int_counter_vec!(
            "pageserver_page_cache_find_victim_calls",
            "Incremented at the end of each find_victim() call.\
             Filter by outcome to get e.g., eviction rate.",
            &["outcome"]
        )
        .unwrap()
    });

    pub(crate) fn observe(outcome: Outcome) {
        macro_rules! dry {
            ($label:literal, $iters:expr) => {{
                static LABEL: &'static str = $label;
                static ITERS_TOTAL: Lazy<IntCounter> =
                    Lazy::new(|| ITERS_TOTAL_VEC.with_label_values(&[LABEL]));
                static CALLS: Lazy<IntCounter> =
                    Lazy::new(|| CALLS_VEC.with_label_values(&[LABEL]));
                ITERS_TOTAL.inc_by(($iters.get()) as u64);
                CALLS.inc();
            }};
        }
        match outcome {
            Outcome::FoundSlotUnused { iters } => dry!("found_empty", iters),
            Outcome::FoundSlotEvicted { iters } => {
                dry!("found_evicted", iters)
            }
            Outcome::ItersExceeded { iters } => {
                dry!("err_iters_exceeded", iters);
                super::page_cache_errors_inc(super::PageCacheErrorKind::EvictIterLimit);
            }
        }
    }
}

static PAGE_CACHE_ERRORS: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "page_cache_errors_total",
        "Number of timeouts while acquiring a pinned slot in the page cache",
        &["error_kind"]
    )
    .expect("failed to define a metric")
});

#[derive(IntoStaticStr)]
#[strum(serialize_all = "kebab_case")]
pub(crate) enum PageCacheErrorKind {
    AcquirePinnedSlotTimeout,
    EvictIterLimit,
}

pub(crate) fn page_cache_errors_inc(error_kind: PageCacheErrorKind) {
    PAGE_CACHE_ERRORS
        .get_metric_with_label_values(&[error_kind.into()])
        .unwrap()
        .inc();
}

pub(crate) static WAIT_LSN_TIME: Lazy<Histogram> = Lazy::new(|| {
    register_histogram!(
        "pageserver_wait_lsn_seconds",
        "Time spent waiting for WAL to arrive. Updated on completion of the wait_lsn operation.",
        CRITICAL_OP_BUCKETS.into(),
    )
    .expect("failed to define a metric")
});

pub(crate) static WAIT_LSN_START_FINISH_COUNTERPAIR: Lazy<IntCounterPairVec> = Lazy::new(|| {
    register_int_counter_pair_vec!(
        "pageserver_wait_lsn_started_count",
        "Number of wait_lsn operations started.",
        "pageserver_wait_lsn_finished_count",
        "Number of wait_lsn operations finished.",
        &["tenant_id", "shard_id", "timeline_id"],
    )
    .expect("failed to define a metric")
});

pub(crate) static WAIT_LSN_IN_PROGRESS_MICROS: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_wait_lsn_in_progress_micros",
        "Time spent waiting for WAL to arrive, by timeline_id. Updated periodically while waiting.",
        &["tenant_id", "shard_id", "timeline_id"],
    )
    .expect("failed to define a metric")
});

pub(crate) static WAIT_LSN_IN_PROGRESS_GLOBAL_MICROS: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_wait_lsn_in_progress_micros_global",
        "Time spent waiting for WAL to arrive, globally. Updated periodically while waiting."
    )
    .expect("failed to define a metric")
});

pub(crate) mod wait_ondemand_download_time {
    use super::*;
    const WAIT_ONDEMAND_DOWNLOAD_TIME_BUCKETS: &[f64] = &[
        0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, // 10 ms - 100ms
        0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, // 100ms to 1s
        1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, // 1s to 10s
        10.0, 20.0, 30.0, 40.0, 50.0, 60.0, // 10s to 1m
    ];

    /// The task kinds for which we want to track wait times for on-demand downloads.
    /// Other task kinds' wait times are accumulated in label value `unknown`.
    pub(crate) const WAIT_ONDEMAND_DOWNLOAD_METRIC_TASK_KINDS: [TaskKind; 2] = [
        TaskKind::PageRequestHandler,
        TaskKind::WalReceiverConnectionHandler,
    ];

    pub(crate) static WAIT_ONDEMAND_DOWNLOAD_TIME_GLOBAL: Lazy<Vec<Histogram>> = Lazy::new(|| {
        let histo = register_histogram_vec!(
            "pageserver_wait_ondemand_download_seconds_global",
            "Observations are individual tasks' wait times for on-demand downloads. \
         If N tasks coalesce on an on-demand download, and it takes 10s, than we observe N * 10s.",
            &["task_kind"],
            WAIT_ONDEMAND_DOWNLOAD_TIME_BUCKETS.into(),
        )
        .expect("failed to define a metric");
        WAIT_ONDEMAND_DOWNLOAD_METRIC_TASK_KINDS
            .iter()
            .map(|task_kind| histo.with_label_values(&[task_kind.into()]))
            .collect::<Vec<_>>()
    });

    pub(crate) static WAIT_ONDEMAND_DOWNLOAD_TIME_SUM: Lazy<CounterVec> = Lazy::new(|| {
        register_counter_vec!(
            // use a name that _could_ be evolved into a per-timeline histogram later
            "pageserver_wait_ondemand_download_seconds_sum",
            "Like `pageserver_wait_ondemand_download_seconds_global` but per timeline",
            &["tenant_id", "shard_id", "timeline_id", "task_kind"],
        )
        .unwrap()
    });

    pub struct WaitOndemandDownloadTimeSum {
        counters: [Counter; WAIT_ONDEMAND_DOWNLOAD_METRIC_TASK_KINDS.len()],
    }

    impl WaitOndemandDownloadTimeSum {
        pub(crate) fn new(tenant_id: &str, shard_id: &str, timeline_id: &str) -> Self {
            let counters = WAIT_ONDEMAND_DOWNLOAD_METRIC_TASK_KINDS
                .iter()
                .map(|task_kind| {
                    WAIT_ONDEMAND_DOWNLOAD_TIME_SUM
                        .get_metric_with_label_values(&[
                            tenant_id,
                            shard_id,
                            timeline_id,
                            task_kind.into(),
                        ])
                        .unwrap()
                })
                .collect::<Vec<_>>();
            Self {
                counters: counters.try_into().unwrap(),
            }
        }
        pub(crate) fn observe(&self, task_kind: TaskKind, duration: Duration) {
            let maybe = WAIT_ONDEMAND_DOWNLOAD_METRIC_TASK_KINDS
                .iter()
                .enumerate()
                .find(|(_, kind)| **kind == task_kind);
            let Some((idx, _)) = maybe else {
                return;
            };
            WAIT_ONDEMAND_DOWNLOAD_TIME_GLOBAL[idx].observe(duration.as_secs_f64());
            let counter = &self.counters[idx];
            counter.inc_by(duration.as_secs_f64());
        }
    }

    pub(crate) fn shutdown_timeline(tenant_id: &str, shard_id: &str, timeline_id: &str) {
        for task_kind in WAIT_ONDEMAND_DOWNLOAD_METRIC_TASK_KINDS {
            let _ = WAIT_ONDEMAND_DOWNLOAD_TIME_SUM.remove_label_values(&[
                tenant_id,
                shard_id,
                timeline_id,
                task_kind.into(),
            ]);
        }
    }

    pub(crate) fn preinitialize_global_metrics() {
        Lazy::force(&WAIT_ONDEMAND_DOWNLOAD_TIME_GLOBAL);
    }
}

static LAST_RECORD_LSN: Lazy<IntGaugeVec> = Lazy::new(|| {
    register_int_gauge_vec!(
        "pageserver_last_record_lsn",
        "Last record LSN grouped by timeline",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

static DISK_CONSISTENT_LSN: Lazy<IntGaugeVec> = Lazy::new(|| {
    register_int_gauge_vec!(
        "pageserver_disk_consistent_lsn",
        "Disk consistent LSN grouped by timeline",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

pub(crate) static PROJECTED_REMOTE_CONSISTENT_LSN: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_projected_remote_consistent_lsn",
        "Projected remote consistent LSN grouped by timeline",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

static PITR_HISTORY_SIZE: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_pitr_history_size",
        "Data written since PITR cutoff on this timeline",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

#[derive(
    strum_macros::EnumIter,
    strum_macros::EnumString,
    strum_macros::Display,
    strum_macros::IntoStaticStr,
)]
#[strum(serialize_all = "kebab_case")]
pub(crate) enum LayerKind {
    Delta,
    Image,
}

#[derive(
    strum_macros::EnumIter,
    strum_macros::EnumString,
    strum_macros::Display,
    strum_macros::IntoStaticStr,
)]
#[strum(serialize_all = "kebab_case")]
pub(crate) enum LayerLevel {
    // We don't track the currently open ephemeral layer, since there's always exactly 1 and its
    // size changes. See `TIMELINE_EPHEMERAL_BYTES`.
    Frozen,
    L0,
    L1,
}

static TIMELINE_LAYER_SIZE: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_layer_bytes",
        "Sum of frozen, L0, and L1 layer physical sizes in bytes (excluding the open ephemeral layer)",
        &["tenant_id", "shard_id", "timeline_id", "level", "kind"]
    )
    .expect("failed to define a metric")
});

static TIMELINE_LAYER_COUNT: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_layer_count",
        "Number of frozen, L0, and L1 layers (excluding the open ephemeral layer)",
        &["tenant_id", "shard_id", "timeline_id", "level", "kind"]
    )
    .expect("failed to define a metric")
});

static TIMELINE_ARCHIVE_SIZE: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_archive_size",
        "Timeline's logical size if it is considered eligible for archival (outside PITR window), else zero",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

static STANDBY_HORIZON: Lazy<IntGaugeVec> = Lazy::new(|| {
    register_int_gauge_vec!(
        "pageserver_standby_horizon",
        "Standby apply LSN for which GC is hold off, by timeline.",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

static RESIDENT_PHYSICAL_SIZE: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_resident_physical_size",
        "The size of the layer files present in the pageserver's filesystem, for attached locations.",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

static VISIBLE_PHYSICAL_SIZE: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_visible_physical_size",
        "The size of the layer files present in the pageserver's filesystem.",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

pub(crate) static RESIDENT_PHYSICAL_SIZE_GLOBAL: Lazy<UIntGauge> = Lazy::new(|| {
    register_uint_gauge!(
        "pageserver_resident_physical_size_global",
        "Like `pageserver_resident_physical_size`, but without tenant/timeline dimensions."
    )
    .expect("failed to define a metric")
});

static REMOTE_PHYSICAL_SIZE: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_remote_physical_size",
        "The size of the layer files present in the remote storage that are listed in the remote index_part.json.",
        // Corollary: If any files are missing from the index part, they won't be included here.
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

static REMOTE_PHYSICAL_SIZE_GLOBAL: Lazy<UIntGauge> = Lazy::new(|| {
    register_uint_gauge!(
        "pageserver_remote_physical_size_global",
        "Like `pageserver_remote_physical_size`, but without tenant/timeline dimensions."
    )
    .expect("failed to define a metric")
});

pub(crate) static REMOTE_ONDEMAND_DOWNLOADED_LAYERS: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_remote_ondemand_downloaded_layers_total",
        "Total on-demand downloaded layers"
    )
    .unwrap()
});

pub(crate) static REMOTE_ONDEMAND_DOWNLOADED_BYTES: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_remote_ondemand_downloaded_bytes_total",
        "Total bytes of layers on-demand downloaded",
    )
    .unwrap()
});

static CURRENT_LOGICAL_SIZE: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_current_logical_size",
        "Current logical size grouped by timeline",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define current logical size metric")
});

static AUX_FILE_SIZE: Lazy<IntGaugeVec> = Lazy::new(|| {
    register_int_gauge_vec!(
        "pageserver_aux_file_estimated_size",
        "The size of all aux files for a timeline in aux file v2 store.",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

static VALID_LSN_LEASE_COUNT: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_valid_lsn_lease_count",
        "The number of valid leases after refreshing gc info.",
        &["tenant_id", "shard_id", "timeline_id"],
    )
    .expect("failed to define a metric")
});

pub(crate) static CIRCUIT_BREAKERS_BROKEN: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_circuit_breaker_broken",
        "How many times a circuit breaker has broken"
    )
    .expect("failed to define a metric")
});

pub(crate) static CIRCUIT_BREAKERS_UNBROKEN: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_circuit_breaker_unbroken",
        "How many times a circuit breaker has been un-broken (recovered)"
    )
    .expect("failed to define a metric")
});

pub(crate) static COMPRESSION_IMAGE_INPUT_BYTES: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_compression_image_in_bytes_total",
        "Size of data written into image layers before compression"
    )
    .expect("failed to define a metric")
});

pub(crate) static COMPRESSION_IMAGE_INPUT_BYTES_CONSIDERED: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_compression_image_in_bytes_considered",
        "Size of potentially compressible data written into image layers before compression"
    )
    .expect("failed to define a metric")
});

pub(crate) static COMPRESSION_IMAGE_INPUT_BYTES_CHOSEN: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_compression_image_in_bytes_chosen",
        "Size of data whose compressed form was written into image layers"
    )
    .expect("failed to define a metric")
});

pub(crate) static COMPRESSION_IMAGE_OUTPUT_BYTES: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_compression_image_out_bytes_total",
        "Size of compressed image layer written"
    )
    .expect("failed to define a metric")
});

pub(crate) static RELSIZE_CACHE_ENTRIES: Lazy<UIntGauge> = Lazy::new(|| {
    register_uint_gauge!(
        "pageserver_relsize_cache_entries",
        "Number of entries in the relation size cache",
    )
    .expect("failed to define a metric")
});

pub(crate) static RELSIZE_CACHE_HITS: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!("pageserver_relsize_cache_hits", "Relation size cache hits",)
        .expect("failed to define a metric")
});

pub(crate) static RELSIZE_CACHE_MISSES: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_relsize_cache_misses",
        "Relation size cache misses",
    )
    .expect("failed to define a metric")
});

pub(crate) static RELSIZE_CACHE_MISSES_OLD: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_relsize_cache_misses_old",
        "Relation size cache misses where the lookup LSN is older than the last relation update"
    )
    .expect("failed to define a metric")
});

pub(crate) mod initial_logical_size {
    use metrics::{IntCounter, IntCounterVec, register_int_counter, register_int_counter_vec};
    use once_cell::sync::Lazy;

    pub(crate) struct StartCalculation(IntCounterVec);
    pub(crate) static START_CALCULATION: Lazy<StartCalculation> = Lazy::new(|| {
        StartCalculation(
            register_int_counter_vec!(
                "pageserver_initial_logical_size_start_calculation",
                "Incremented each time we start an initial logical size calculation attempt. \
                 The `circumstances` label provides some additional details.",
                &["attempt", "circumstances"]
            )
            .unwrap(),
        )
    });

    struct DropCalculation {
        first: IntCounter,
        retry: IntCounter,
    }

    static DROP_CALCULATION: Lazy<DropCalculation> = Lazy::new(|| {
        let vec = register_int_counter_vec!(
            "pageserver_initial_logical_size_drop_calculation",
            "Incremented each time we abort a started size calculation attmpt.",
            &["attempt"]
        )
        .unwrap();
        DropCalculation {
            first: vec.with_label_values(&["first"]),
            retry: vec.with_label_values(&["retry"]),
        }
    });

    pub(crate) struct Calculated {
        pub(crate) births: IntCounter,
        pub(crate) deaths: IntCounter,
    }

    pub(crate) static CALCULATED: Lazy<Calculated> = Lazy::new(|| Calculated {
        births: register_int_counter!(
            "pageserver_initial_logical_size_finish_calculation",
            "Incremented every time we finish calculation of initial logical size.\
             If everything is working well, this should happen at most once per Timeline object."
        )
        .unwrap(),
        deaths: register_int_counter!(
            "pageserver_initial_logical_size_drop_finished_calculation",
            "Incremented when we drop a finished initial logical size calculation result.\
             Mainly useful to turn pageserver_initial_logical_size_finish_calculation into a gauge."
        )
        .unwrap(),
    });

    pub(crate) struct OngoingCalculationGuard {
        inc_drop_calculation: Option<IntCounter>,
    }

    #[derive(strum_macros::IntoStaticStr)]
    pub(crate) enum StartCircumstances {
        EmptyInitial,
        SkippedConcurrencyLimiter,
        AfterBackgroundTasksRateLimit,
    }

    impl StartCalculation {
        pub(crate) fn first(&self, circumstances: StartCircumstances) -> OngoingCalculationGuard {
            let circumstances_label: &'static str = circumstances.into();
            self.0
                .with_label_values(&["first", circumstances_label])
                .inc();
            OngoingCalculationGuard {
                inc_drop_calculation: Some(DROP_CALCULATION.first.clone()),
            }
        }
        pub(crate) fn retry(&self, circumstances: StartCircumstances) -> OngoingCalculationGuard {
            let circumstances_label: &'static str = circumstances.into();
            self.0
                .with_label_values(&["retry", circumstances_label])
                .inc();
            OngoingCalculationGuard {
                inc_drop_calculation: Some(DROP_CALCULATION.retry.clone()),
            }
        }
    }

    impl Drop for OngoingCalculationGuard {
        fn drop(&mut self) {
            if let Some(counter) = self.inc_drop_calculation.take() {
                counter.inc();
            }
        }
    }

    impl OngoingCalculationGuard {
        pub(crate) fn calculation_result_saved(mut self) -> FinishedCalculationGuard {
            drop(self.inc_drop_calculation.take());
            CALCULATED.births.inc();
            FinishedCalculationGuard {
                inc_on_drop: CALCULATED.deaths.clone(),
            }
        }
    }

    pub(crate) struct FinishedCalculationGuard {
        inc_on_drop: IntCounter,
    }

    impl Drop for FinishedCalculationGuard {
        fn drop(&mut self) {
            self.inc_on_drop.inc();
        }
    }

    // context: https://github.com/neondatabase/neon/issues/5963
    pub(crate) static TIMELINES_WHERE_WALRECEIVER_GOT_APPROXIMATE_SIZE: Lazy<IntCounter> =
        Lazy::new(|| {
            register_int_counter!(
                "pageserver_initial_logical_size_timelines_where_walreceiver_got_approximate_size",
                "Counter for the following event: walreceiver calls\
                 Timeline::get_current_logical_size() and it returns `Approximate` for the first time."
            )
            .unwrap()
        });
}

static DIRECTORY_ENTRIES_COUNT: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_directory_entries_count",
        "Sum of the entries in pageserver-stored directory listings",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

pub(crate) static TENANT_STATE_METRIC: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_tenant_states_count",
        "Count of tenants per state",
        &["state"]
    )
    .expect("Failed to register pageserver_tenant_states_count metric")
});

/// A set of broken tenants.
///
/// These are expected to be so rare that a set is fine. Set as in a new timeseries per each broken
/// tenant.
pub(crate) static BROKEN_TENANTS_SET: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_broken_tenants_count",
        "Set of broken tenants",
        &["tenant_id", "shard_id"]
    )
    .expect("Failed to register pageserver_tenant_states_count metric")
});

pub(crate) static TENANT_SYNTHETIC_SIZE_METRIC: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_tenant_synthetic_cached_size_bytes",
        "Synthetic size of each tenant in bytes",
        &["tenant_id"]
    )
    .expect("Failed to register pageserver_tenant_synthetic_cached_size_bytes metric")
});

pub(crate) static EVICTION_ITERATION_DURATION: Lazy<HistogramVec> = Lazy::new(|| {
    register_histogram_vec!(
        "pageserver_eviction_iteration_duration_seconds_global",
        "Time spent on a single eviction iteration",
        &["period_secs", "threshold_secs"],
        STORAGE_OP_BUCKETS.into(),
    )
    .expect("failed to define a metric")
});

static EVICTIONS: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_evictions",
        "Number of layers evicted from the pageserver",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

static EVICTIONS_WITH_LOW_RESIDENCE_DURATION: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_evictions_with_low_residence_duration",
        "If a layer is evicted that was resident for less than `low_threshold`, it is counted to this counter. \
         Residence duration is determined using the `residence_duration_data_source`.",
        &["tenant_id", "shard_id", "timeline_id", "residence_duration_data_source", "low_threshold_secs"]
    )
    .expect("failed to define a metric")
});

pub(crate) static UNEXPECTED_ONDEMAND_DOWNLOADS: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_unexpected_ondemand_downloads_count",
        "Number of unexpected on-demand downloads. \
         We log more context for each increment, so, forgo any labels in this metric.",
    )
    .expect("failed to define a metric")
});

/// How long did we take to start up?  Broken down by labels to describe
/// different phases of startup.
pub static STARTUP_DURATION: Lazy<GaugeVec> = Lazy::new(|| {
    register_gauge_vec!(
        "pageserver_startup_duration_seconds",
        "Time taken by phases of pageserver startup, in seconds",
        &["phase"]
    )
    .expect("Failed to register pageserver_startup_duration_seconds metric")
});

pub static STARTUP_IS_LOADING: Lazy<UIntGauge> = Lazy::new(|| {
    register_uint_gauge!(
        "pageserver_startup_is_loading",
        "1 while in initial startup load of tenants, 0 at other times"
    )
    .expect("Failed to register pageserver_startup_is_loading")
});

pub(crate) static TIMELINE_EPHEMERAL_BYTES: Lazy<UIntGauge> = Lazy::new(|| {
    register_uint_gauge!(
        "pageserver_timeline_ephemeral_bytes",
        "Total number of bytes in ephemeral layers, summed for all timelines.  Approximate, lazily updated."
    )
    .expect("Failed to register metric")
});

/// Metrics related to the lifecycle of a [`crate::tenant::TenantShard`] object: things
/// like how long it took to load.
///
/// Note that these are process-global metrics, _not_ per-tenant metrics.  Per-tenant
/// metrics are rather expensive, and usually fine grained stuff makes more sense
/// at a timeline level than tenant level.
pub(crate) struct TenantMetrics {
    /// How long did tenants take to go from construction to active state?
    pub(crate) activation: Histogram,
    pub(crate) preload: Histogram,
    pub(crate) attach: Histogram,

    /// How many tenants are included in the initial startup of the pagesrever?
    pub(crate) startup_scheduled: IntCounter,
    pub(crate) startup_complete: IntCounter,
}

pub(crate) static TENANT: Lazy<TenantMetrics> = Lazy::new(|| {
    TenantMetrics {
    activation: register_histogram!(
        "pageserver_tenant_activation_seconds",
        "Time taken by tenants to activate, in seconds",
        CRITICAL_OP_BUCKETS.into()
    )
    .expect("Failed to register metric"),
    preload: register_histogram!(
        "pageserver_tenant_preload_seconds",
        "Time taken by tenants to load remote metadata on startup/attach, in seconds",
        CRITICAL_OP_BUCKETS.into()
    )
    .expect("Failed to register metric"),
    attach: register_histogram!(
        "pageserver_tenant_attach_seconds",
        "Time taken by tenants to intialize, after remote metadata is already loaded",
        CRITICAL_OP_BUCKETS.into()
    )
    .expect("Failed to register metric"),
    startup_scheduled: register_int_counter!(
        "pageserver_tenant_startup_scheduled",
        "Number of tenants included in pageserver startup (doesn't count tenants attached later)"
    ).expect("Failed to register metric"),
    startup_complete: register_int_counter!(
        "pageserver_tenant_startup_complete",
        "Number of tenants that have completed warm-up, or activated on-demand during initial startup: \
         should eventually reach `pageserver_tenant_startup_scheduled_total`.  Does not include broken \
         tenants: such cases will lead to this metric never reaching the scheduled count."
    ).expect("Failed to register metric"),
}
});

/// Each `Timeline`'s  [`EVICTIONS_WITH_LOW_RESIDENCE_DURATION`] metric.
#[derive(Debug)]
pub(crate) struct EvictionsWithLowResidenceDuration {
    data_source: &'static str,
    threshold: Duration,
    counter: Option<IntCounter>,
}

pub(crate) struct EvictionsWithLowResidenceDurationBuilder {
    data_source: &'static str,
    threshold: Duration,
}

impl EvictionsWithLowResidenceDurationBuilder {
    pub fn new(data_source: &'static str, threshold: Duration) -> Self {
        Self {
            data_source,
            threshold,
        }
    }

    fn build(
        &self,
        tenant_id: &str,
        shard_id: &str,
        timeline_id: &str,
    ) -> EvictionsWithLowResidenceDuration {
        let counter = EVICTIONS_WITH_LOW_RESIDENCE_DURATION
            .get_metric_with_label_values(&[
                tenant_id,
                shard_id,
                timeline_id,
                self.data_source,
                &EvictionsWithLowResidenceDuration::threshold_label_value(self.threshold),
            ])
            .unwrap();
        EvictionsWithLowResidenceDuration {
            data_source: self.data_source,
            threshold: self.threshold,
            counter: Some(counter),
        }
    }
}

impl EvictionsWithLowResidenceDuration {
    fn threshold_label_value(threshold: Duration) -> String {
        format!("{}", threshold.as_secs())
    }

    pub fn observe(&self, observed_value: Duration) {
        if observed_value < self.threshold {
            self.counter
                .as_ref()
                .expect("nobody calls this function after `remove_from_vec`")
                .inc();
        }
    }

    pub fn change_threshold(
        &mut self,
        tenant_id: &str,
        shard_id: &str,
        timeline_id: &str,
        new_threshold: Duration,
    ) {
        if new_threshold == self.threshold {
            return;
        }
        let mut with_new = EvictionsWithLowResidenceDurationBuilder::new(
            self.data_source,
            new_threshold,
        )
        .build(tenant_id, shard_id, timeline_id);
        std::mem::swap(self, &mut with_new);
        with_new.remove(tenant_id, shard_id, timeline_id);
    }

    // This could be a `Drop` impl, but, we need the `tenant_id` and `timeline_id`.
    fn remove(&mut self, tenant_id: &str, shard_id: &str, timeline_id: &str) {
        let Some(_counter) = self.counter.take() else {
            return;
        };

        let threshold = Self::threshold_label_value(self.threshold);

        let removed = EVICTIONS_WITH_LOW_RESIDENCE_DURATION.remove_label_values(&[
            tenant_id,
            shard_id,
            timeline_id,
            self.data_source,
            &threshold,
        ]);

        match removed {
            Err(e) => {
                // this has been hit in staging as
                // <https://neondatabase.sentry.io/issues/4142396994/>, but we don't know how.
                // because we can be in the drop path already, don't risk:
                // - "double-panic => illegal instruction" or
                // - future "drop panick => abort"
                //
                // so just nag: (the error has the labels)
                tracing::warn!(
                    "failed to remove EvictionsWithLowResidenceDuration, it was already removed? {e:#?}"
                );
            }
            Ok(()) => {
                // to help identify cases where we double-remove the same values, let's log all
                // deletions?
                tracing::info!(
                    "removed EvictionsWithLowResidenceDuration with {tenant_id}, {timeline_id}, {}, {threshold}",
                    self.data_source
                );
            }
        }
    }
}

// Metrics collected on disk IO operations
//
// Roughly logarithmic scale.
const STORAGE_IO_TIME_BUCKETS: &[f64] = &[
    0.000030, // 30 usec
    0.001000, // 1000 usec
    0.030,    // 30 ms
    1.000,    // 1000 ms
    30.000,   // 30000 ms
];

/// VirtualFile fs operation variants.
///
/// Operations:
/// - open ([`std::fs::OpenOptions::open`])
/// - close (dropping [`crate::virtual_file::VirtualFile`])
/// - close-by-replace (close by replacement algorithm)
/// - read (`read_at`)
/// - write (`write_at`)
/// - seek (modify internal position or file length query)
/// - fsync ([`std::fs::File::sync_all`])
/// - metadata ([`std::fs::File::metadata`])
#[derive(
    Debug, Clone, Copy, strum_macros::EnumCount, strum_macros::EnumIter, strum_macros::FromRepr,
)]
pub(crate) enum StorageIoOperation {
    Open,
    OpenAfterReplace,
    Close,
    CloseByReplace,
    Read,
    Write,
    Seek,
    Fsync,
    Metadata,
    SetLen,
}

impl StorageIoOperation {
    pub fn as_str(&self) -> &'static str {
        match self {
            StorageIoOperation::Open => "open",
            StorageIoOperation::OpenAfterReplace => "open-after-replace",
            StorageIoOperation::Close => "close",
            StorageIoOperation::CloseByReplace => "close-by-replace",
            StorageIoOperation::Read => "read",
            StorageIoOperation::Write => "write",
            StorageIoOperation::Seek => "seek",
            StorageIoOperation::Fsync => "fsync",
            StorageIoOperation::Metadata => "metadata",
            StorageIoOperation::SetLen => "set_len",
        }
    }
}

/// Tracks time taken by fs operations near VirtualFile.
#[derive(Debug)]
pub(crate) struct StorageIoTime {
    metrics: [Histogram; StorageIoOperation::COUNT],
}

impl StorageIoTime {
    fn new() -> Self {
        let storage_io_histogram_vec = register_histogram_vec!(
            "pageserver_io_operations_seconds",
            "Time spent in IO operations",
            &["operation"],
            STORAGE_IO_TIME_BUCKETS.into()
        )
        .expect("failed to define a metric");
        let metrics = std::array::from_fn(|i| {
            let op = StorageIoOperation::from_repr(i).unwrap();
            storage_io_histogram_vec
                .get_metric_with_label_values(&[op.as_str()])
                .unwrap()
        });
        Self { metrics }
    }

    pub(crate) fn get(&self, op: StorageIoOperation) -> &Histogram {
        &self.metrics[op as usize]
    }
}

pub(crate) static STORAGE_IO_TIME_METRIC: Lazy<StorageIoTime> = Lazy::new(StorageIoTime::new);

#[derive(Clone, Copy)]
#[repr(usize)]
pub(crate) enum StorageIoSizeOperation {
    Read,
    Write,
}

impl StorageIoSizeOperation {
    pub(crate) const VARIANTS: &'static [&'static str] = &["read", "write"];

    fn as_str(&self) -> &'static str {
        Self::VARIANTS[*self as usize]
    }
}

// Needed for the https://neonprod.grafana.net/d/5uK9tHL4k/picking-tenant-for-relocation?orgId=1
pub(crate) static STORAGE_IO_SIZE: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_io_operations_bytes_total",
        "Total amount of bytes read/written in IO operations",
        &["operation", "tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

#[derive(Clone, Debug)]
pub(crate) struct StorageIoSizeMetrics {
    pub read: UIntGauge,
    pub write: UIntGauge,
}

impl StorageIoSizeMetrics {
    pub(crate) fn new(tenant_id: &str, shard_id: &str, timeline_id: &str) -> Self {
        let read = STORAGE_IO_SIZE
            .get_metric_with_label_values(&[
                StorageIoSizeOperation::Read.as_str(),
                tenant_id,
                shard_id,
                timeline_id,
            ])
            .unwrap();
        let write = STORAGE_IO_SIZE
            .get_metric_with_label_values(&[
                StorageIoSizeOperation::Write.as_str(),
                tenant_id,
                shard_id,
                timeline_id,
            ])
            .unwrap();
        Self { read, write }
    }
}

#[cfg(not(test))]
pub(crate) mod virtual_file_descriptor_cache {
    use super::*;

    pub(crate) static SIZE_MAX: Lazy<UIntGauge> = Lazy::new(|| {
        register_uint_gauge!(
            "pageserver_virtual_file_descriptor_cache_size_max",
            "Maximum number of open file descriptors in the cache."
        )
        .unwrap()
    });

    // SIZE_CURRENT: derive it like so:
    // ```
    // sum (pageserver_io_operations_seconds_count{operation=~"^(open|open-after-replace)$")
    // -ignoring(operation)
    // sum(pageserver_io_operations_seconds_count{operation=~"^(close|close-by-replace)$"}
    // ```
}

#[cfg(not(test))]
pub(crate) mod virtual_file_io_engine {
    use super::*;

    pub(crate) static KIND: Lazy<UIntGaugeVec> = Lazy::new(|| {
        register_uint_gauge_vec!(
            "pageserver_virtual_file_io_engine_kind",
            "The configured io engine for VirtualFile",
            &["kind"],
        )
        .unwrap()
    });
}

pub(crate) struct SmgrOpTimer(Option<SmgrOpTimerInner>);
pub(crate) struct SmgrOpTimerInner {
    global_execution_latency_histo: Histogram,
    per_timeline_execution_latency_histo: Option<Histogram>,

    global_batch_wait_time: Histogram,
    per_timeline_batch_wait_time: Histogram,

    global_flush_in_progress_micros: IntCounter,
    per_timeline_flush_in_progress_micros: IntCounter,

    throttling: Arc<tenant_throttling::Pagestream>,

    timings: SmgrOpTimerState,
}

/// The stages of request processing are represented by the enum variants.
/// Used as part of [`SmgrOpTimerInner::timings`].
///
/// Request processing calls into the `SmgrOpTimer::observe_*` methods at the
/// transition points.
/// These methods bump relevant counters and then update [`SmgrOpTimerInner::timings`]
/// to the next state.
///
/// Each request goes through every stage, in all configurations.
///
#[derive(Debug)]
enum SmgrOpTimerState {
    Received {
        // In the future, we may want to track the full time the request spent
        // inside pageserver process (time spent in kernel buffers can't be tracked).
        // `received_at` would be used for that.
        #[allow(dead_code)]
        received_at: Instant,
    },
    Throttling {
        throttle_started_at: Instant,
    },
    Batching {
        throttle_done_at: Instant,
    },
    Executing {
        execution_started_at: Instant,
    },
    Flushing,
    // NB: when adding observation points, remember to update the Drop impl.
}

// NB: when adding observation points, remember to update the Drop impl.
impl SmgrOpTimer {
    /// See [`SmgrOpTimerState`] for more context.
    pub(crate) fn observe_throttle_start(&mut self, at: Instant) {
        let Some(inner) = self.0.as_mut() else {
            return;
        };
        let SmgrOpTimerState::Received { received_at: _ } = &mut inner.timings else {
            return;
        };
        inner.throttling.count_accounted_start.inc();
        inner.timings = SmgrOpTimerState::Throttling {
            throttle_started_at: at,
        };
    }

    /// See [`SmgrOpTimerState`] for more context.
    pub(crate) fn observe_throttle_done(&mut self, throttle: ThrottleResult) {
        let Some(inner) = self.0.as_mut() else {
            return;
        };
        let SmgrOpTimerState::Throttling {
            throttle_started_at,
        } = &inner.timings
        else {
            return;
        };
        inner.throttling.count_accounted_finish.inc();
        match throttle {
            ThrottleResult::NotThrottled { end } => {
                inner.timings = SmgrOpTimerState::Batching {
                    throttle_done_at: end,
                };
            }
            ThrottleResult::Throttled { end } => {
                // update metrics
                inner.throttling.count_throttled.inc();
                inner
                    .throttling
                    .wait_time
                    .inc_by((end - *throttle_started_at).as_micros().try_into().unwrap());
                // state transition
                inner.timings = SmgrOpTimerState::Batching {
                    throttle_done_at: end,
                };
            }
        }
    }

    /// See [`SmgrOpTimerState`] for more context.
    pub(crate) fn observe_execution_start(&mut self, at: Instant) {
        let Some(inner) = self.0.as_mut() else {
            return;
        };
        let SmgrOpTimerState::Batching { throttle_done_at } = &inner.timings else {
            return;
        };
        // update metrics
        let batch = at - *throttle_done_at;
        inner.global_batch_wait_time.observe(batch.as_secs_f64());
        inner
            .per_timeline_batch_wait_time
            .observe(batch.as_secs_f64());
        // state transition
        inner.timings = SmgrOpTimerState::Executing {
            execution_started_at: at,
        }
    }

    /// For all but the first caller, this is a no-op.
    /// The first callers receives Some, subsequent ones None.
    ///
    /// See [`SmgrOpTimerState`] for more context.
    pub(crate) fn observe_execution_end(&mut self, at: Instant) -> Option<SmgrOpFlushInProgress> {
        // NB: unlike the other observe_* methods, this one take()s.
        #[allow(clippy::question_mark)] // maintain similar code pattern.
        let Some(mut inner) = self.0.take() else {
            return None;
        };
        let SmgrOpTimerState::Executing {
            execution_started_at,
        } = &inner.timings
        else {
            return None;
        };
        // update metrics
        let execution = at - *execution_started_at;
        inner
            .global_execution_latency_histo
            .observe(execution.as_secs_f64());
        if let Some(per_timeline_execution_latency_histo) =
            &inner.per_timeline_execution_latency_histo
        {
            per_timeline_execution_latency_histo.observe(execution.as_secs_f64());
        }

        // state transition
        inner.timings = SmgrOpTimerState::Flushing;

        // return the flush in progress object which
        // will do the remaining metrics updates
        let SmgrOpTimerInner {
            global_flush_in_progress_micros,
            per_timeline_flush_in_progress_micros,
            ..
        } = inner;
        Some(SmgrOpFlushInProgress {
            global_micros: global_flush_in_progress_micros,
            per_timeline_micros: per_timeline_flush_in_progress_micros,
        })
    }
}

/// The last stage of request processing is serializing and flushing the request
/// into the TCP connection. We want to make slow flushes observable
/// _while they are occuring_, so this struct provides a wrapper method [`Self::measure`]
/// to periodically bump the metric.
///
/// If in the future we decide that we're not interested in live updates, we can
/// add another `observe_*` method to [`SmgrOpTimer`], follow the existing pattern there,
/// and remove this struct from the code base.
pub(crate) struct SmgrOpFlushInProgress {
    global_micros: IntCounter,
    per_timeline_micros: IntCounter,
}

impl Drop for SmgrOpTimer {
    fn drop(&mut self) {
        // In case of early drop, update any of the remaining metrics with
        // observations so that (started,finished) counter pairs balance out
        // and all counters on the latency path have the the same number of
        // observations.
        // It's technically lying and it would be better if each metric had
        // a separate label or similar for cancelled requests.
        // But we don't have that right now and counter pairs balancing
        // out is useful when using the metrics in panels and whatnot.
        let now = Instant::now();
        self.observe_throttle_start(now);
        self.observe_throttle_done(ThrottleResult::NotThrottled { end: now });
        self.observe_execution_start(now);
        let maybe_flush_timer = self.observe_execution_end(now);
        drop(maybe_flush_timer);
    }
}

impl SmgrOpFlushInProgress {
    /// The caller must guarantee that `socket_fd`` outlives this function.
    pub(crate) async fn measure<Fut, O>(
        self,
        started_at: Instant,
        mut fut: Fut,
        socket_fd: RawFd,
    ) -> O
    where
        Fut: std::future::Future<Output = O>,
    {
        let mut fut = std::pin::pin!(fut);

        let mut logged = false;
        let mut last_counter_increment_at = started_at;
        let mut observe_guard = scopeguard::guard(
            |is_timeout| {
                let now = Instant::now();

                // Increment counter
                {
                    let elapsed_since_last_observe = now - last_counter_increment_at;
                    self.global_micros
                        .inc_by(u64::try_from(elapsed_since_last_observe.as_micros()).unwrap());
                    self.per_timeline_micros
                        .inc_by(u64::try_from(elapsed_since_last_observe.as_micros()).unwrap());
                    last_counter_increment_at = now;
                }

                // Log something on every timeout, and on completion but only if we hit a timeout.
                if is_timeout || logged {
                    logged = true;
                    let elapsed_total = now - started_at;
                    let msg = if is_timeout {
                        "slow flush ongoing"
                    } else {
                        "slow flush completed or cancelled"
                    };

                    let (inq, outq) = {
                        // SAFETY: caller guarantees that `socket_fd` outlives this function.
                        #[cfg(target_os = "linux")]
                        unsafe {
                            (
                                utils::linux_socket_ioctl::inq(socket_fd).unwrap_or(-2),
                                utils::linux_socket_ioctl::outq(socket_fd).unwrap_or(-2),
                            )
                        }
                        #[cfg(not(target_os = "linux"))]
                        {
                            _ = socket_fd; // appease unused lint on macOS
                            (-1, -1)
                        }
                    };

                    let elapsed_total_secs = format!("{:.6}", elapsed_total.as_secs_f64());
                    tracing::info!(elapsed_total_secs, inq, outq, msg);
                }
            },
            |mut observe| {
                observe(false);
            },
        );

        loop {
            match tokio::time::timeout(Duration::from_secs(10), &mut fut).await {
                Ok(v) => return v,
                Err(_timeout) => {
                    (*observe_guard)(true);
                }
            }
        }
    }
}

#[derive(
    Debug,
    Clone,
    Copy,
    IntoStaticStr,
    strum_macros::EnumCount,
    strum_macros::EnumIter,
    strum_macros::FromRepr,
    enum_map::Enum,
)]
#[strum(serialize_all = "snake_case")]
pub enum SmgrQueryType {
    GetRelExists,
    GetRelSize,
    GetPageAtLsn,
    GetDbSize,
    GetSlruSegment,
    #[cfg(feature = "testing")]
    Test,
}

#[derive(
    Debug,
    Clone,
    Copy,
    IntoStaticStr,
    strum_macros::EnumCount,
    strum_macros::EnumIter,
    strum_macros::FromRepr,
    enum_map::Enum,
)]
#[strum(serialize_all = "snake_case")]
pub enum GetPageBatchBreakReason {
    BatchFull,
    NonBatchableRequest,
    NonUniformLsn,
    SamePageAtDifferentLsn,
    NonUniformTimeline,
    ExecutorSteal,
    #[cfg(feature = "testing")]
    NonUniformKey,
}

pub(crate) struct SmgrQueryTimePerTimeline {
    global_started: [IntCounter; SmgrQueryType::COUNT],
    global_latency: [Histogram; SmgrQueryType::COUNT],
    per_timeline_getpage_started: IntCounter,
    per_timeline_getpage_latency: Histogram,
    global_batch_size: Histogram,
    per_timeline_batch_size: Histogram,
    global_flush_in_progress_micros: IntCounter,
    per_timeline_flush_in_progress_micros: IntCounter,
    global_batch_wait_time: Histogram,
    per_timeline_batch_wait_time: Histogram,
    global_batch_break_reason: [IntCounter; GetPageBatchBreakReason::COUNT],
    per_timeline_batch_break_reason: GetPageBatchBreakReasonTimelineMetrics,
    throttling: Arc<tenant_throttling::Pagestream>,
}

static SMGR_QUERY_STARTED_GLOBAL: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        // it's a counter, but, name is prepared to extend it to a histogram of queue depth
        "pageserver_smgr_query_started_global_count",
        "Number of smgr queries started, aggregated by query type.",
        &["smgr_query_type"],
    )
    .expect("failed to define a metric")
});

static SMGR_QUERY_STARTED_PER_TENANT_TIMELINE: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        // it's a counter, but, name is prepared to extend it to a histogram of queue depth
        "pageserver_smgr_query_started_count",
        "Number of smgr queries started, aggregated by query type and tenant/timeline.",
        &["smgr_query_type", "tenant_id", "shard_id", "timeline_id"],
    )
    .expect("failed to define a metric")
});

// Alias so all histograms recording per-timeline smgr timings use the same buckets.
static SMGR_QUERY_TIME_PER_TENANT_TIMELINE_BUCKETS: &[f64] = CRITICAL_OP_BUCKETS;

static SMGR_QUERY_TIME_PER_TENANT_TIMELINE: Lazy<HistogramVec> = Lazy::new(|| {
    register_histogram_vec!(
        "pageserver_smgr_query_seconds",
        "Time spent _executing_ smgr query handling, excluding batch and throttle delays.",
        &["smgr_query_type", "tenant_id", "shard_id", "timeline_id"],
        SMGR_QUERY_TIME_PER_TENANT_TIMELINE_BUCKETS.into(),
    )
    .expect("failed to define a metric")
});

static SMGR_QUERY_TIME_GLOBAL_BUCKETS: Lazy<Vec<f64>> = Lazy::new(|| {
    [
        1,
        10,
        20,
        40,
        60,
        80,
        100,
        200,
        300,
        400,
        500,
        600,
        700,
        800,
        900,
        1_000, // 1ms
        2_000,
        4_000,
        6_000,
        8_000,
        10_000, // 10ms
        20_000,
        40_000,
        60_000,
        80_000,
        100_000,
        200_000,
        400_000,
        600_000,
        800_000,
        1_000_000, // 1s
        2_000_000,
        4_000_000,
        6_000_000,
        8_000_000,
        10_000_000, // 10s
        20_000_000,
        50_000_000,
        100_000_000,
        200_000_000,
        1_000_000_000, // 1000s
    ]
    .into_iter()
    .map(Duration::from_micros)
    .map(|d| d.as_secs_f64())
    .collect()
});

static SMGR_QUERY_TIME_GLOBAL: Lazy<HistogramVec> = Lazy::new(|| {
    register_histogram_vec!(
        "pageserver_smgr_query_seconds_global",
        "Like pageserver_smgr_query_seconds, but aggregated to instance level.",
        &["smgr_query_type"],
        SMGR_QUERY_TIME_GLOBAL_BUCKETS.clone(),
    )
    .expect("failed to define a metric")
});

static PAGE_SERVICE_BATCH_SIZE_BUCKETS_GLOBAL: Lazy<Vec<f64>> = Lazy::new(|| {
    (1..=u32::try_from(Timeline::MAX_GET_VECTORED_KEYS).unwrap())
        .map(|v| v.into())
        .collect()
});

static PAGE_SERVICE_BATCH_SIZE_GLOBAL: Lazy<Histogram> = Lazy::new(|| {
    register_histogram!(
        "pageserver_page_service_batch_size_global",
        "Batch size of pageserver page service requests",
        PAGE_SERVICE_BATCH_SIZE_BUCKETS_GLOBAL.clone(),
    )
    .expect("failed to define a metric")
});

static PAGE_SERVICE_BATCH_SIZE_BUCKETS_PER_TIMELINE: Lazy<Vec<f64>> = Lazy::new(|| {
    let mut buckets = Vec::new();
    for i in 0.. {
        let bucket = 1 << i;
        if bucket > u32::try_from(Timeline::MAX_GET_VECTORED_KEYS).unwrap() {
            break;
        }
        buckets.push(bucket.into());
    }
    buckets
});

static PAGE_SERVICE_BATCH_SIZE_PER_TENANT_TIMELINE: Lazy<HistogramVec> = Lazy::new(|| {
    register_histogram_vec!(
        "pageserver_page_service_batch_size",
        "Batch size of pageserver page service requests",
        &["tenant_id", "shard_id", "timeline_id"],
        PAGE_SERVICE_BATCH_SIZE_BUCKETS_PER_TIMELINE.clone()
    )
    .expect("failed to define a metric")
});

static PAGE_SERVICE_BATCH_BREAK_REASON_GLOBAL: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        // it's a counter, but, name is prepared to extend it to a histogram of queue depth
        "pageserver_page_service_batch_break_reason_global",
        "Reason for breaking batches of get page requests",
        &["reason"],
    )
    .expect("failed to define a metric")
});

struct GetPageBatchBreakReasonTimelineMetrics {
    map: EnumMap<GetPageBatchBreakReason, IntCounter>,
}

impl GetPageBatchBreakReasonTimelineMetrics {
    fn new(tenant_id: &str, shard_slug: &str, timeline_id: &str) -> Self {
        GetPageBatchBreakReasonTimelineMetrics {
            map: EnumMap::from_array(std::array::from_fn(|reason_idx| {
                let reason = GetPageBatchBreakReason::from_usize(reason_idx);
                PAGE_SERVICE_BATCH_BREAK_REASON_PER_TENANT_TIMELINE.with_label_values(&[
                    tenant_id,
                    shard_slug,
                    timeline_id,
                    reason.into(),
                ])
            })),
        }
    }

    fn inc(&self, reason: GetPageBatchBreakReason) {
        self.map[reason].inc()
    }
}

static PAGE_SERVICE_BATCH_BREAK_REASON_PER_TENANT_TIMELINE: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_page_service_batch_break_reason",
        "Reason for breaking batches of get page requests",
        &["tenant_id", "shard_id", "timeline_id", "reason"],
    )
    .expect("failed to define a metric")
});

pub(crate) static PAGE_SERVICE_CONFIG_MAX_BATCH_SIZE: Lazy<IntGaugeVec> = Lazy::new(|| {
    register_int_gauge_vec!(
        "pageserver_page_service_config_max_batch_size",
        "Configured maximum batch size for the server-side batching functionality of page_service. \
         Labels expose more of the configuration parameters.",
        &["mode", "execution", "batching"]
    )
    .expect("failed to define a metric")
});

fn set_page_service_config_max_batch_size(conf: &PageServicePipeliningConfig) {
    PAGE_SERVICE_CONFIG_MAX_BATCH_SIZE.reset();
    let (label_values, value) = match conf {
        PageServicePipeliningConfig::Serial => (["serial", "-", "-"], 1),
        PageServicePipeliningConfig::Pipelined(PageServicePipeliningConfigPipelined {
            max_batch_size,
            execution,
            batching,
        }) => {
            let mode = "pipelined";
            let execution = match execution {
                PageServiceProtocolPipelinedExecutionStrategy::ConcurrentFutures => {
                    "concurrent-futures"
                }
                PageServiceProtocolPipelinedExecutionStrategy::Tasks => "tasks",
            };
            let batching = match batching {
                PageServiceProtocolPipelinedBatchingStrategy::UniformLsn => "uniform-lsn",
                PageServiceProtocolPipelinedBatchingStrategy::ScatteredLsn => "scattered-lsn",
            };

            ([mode, execution, batching], max_batch_size.get())
        }
    };
    PAGE_SERVICE_CONFIG_MAX_BATCH_SIZE
        .with_label_values(&label_values)
        .set(value.try_into().unwrap());
}

static PAGE_SERVICE_SMGR_FLUSH_INPROGRESS_MICROS: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_page_service_pagestream_flush_in_progress_micros",
        "Counter that sums up the microseconds that a pagestream response was being flushed into the TCP connection. \
         If the flush is particularly slow, this counter will be updated periodically to make slow flushes \
         easily discoverable in monitoring. \
         Hence, this is NOT a completion latency historgram.",
        &["tenant_id", "shard_id", "timeline_id"],
    )
    .expect("failed to define a metric")
});

static PAGE_SERVICE_SMGR_FLUSH_INPROGRESS_MICROS_GLOBAL: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_page_service_pagestream_flush_in_progress_micros_global",
        "Like pageserver_page_service_pagestream_flush_in_progress_seconds, but instance-wide.",
    )
    .expect("failed to define a metric")
});

static PAGE_SERVICE_SMGR_BATCH_WAIT_TIME: Lazy<HistogramVec> = Lazy::new(|| {
    register_histogram_vec!(
        "pageserver_page_service_pagestream_batch_wait_time_seconds",
        "Time a request spent waiting in its batch until the batch moved to throttle&execution.",
        &["tenant_id", "shard_id", "timeline_id"],
        SMGR_QUERY_TIME_PER_TENANT_TIMELINE_BUCKETS.into(),
    )
    .expect("failed to define a metric")
});

static PAGE_SERVICE_SMGR_BATCH_WAIT_TIME_GLOBAL: Lazy<Histogram> = Lazy::new(|| {
    register_histogram!(
        "pageserver_page_service_pagestream_batch_wait_time_seconds_global",
        "Like pageserver_page_service_pagestream_batch_wait_time_seconds, but aggregated to instance level.",
        SMGR_QUERY_TIME_GLOBAL_BUCKETS.to_vec(),
    )
    .expect("failed to define a metric")
});

impl SmgrQueryTimePerTimeline {
    pub(crate) fn new(
        tenant_shard_id: &TenantShardId,
        timeline_id: &TimelineId,
        pagestream_throttle_metrics: Arc<tenant_throttling::Pagestream>,
    ) -> Self {
        let tenant_id = tenant_shard_id.tenant_id.to_string();
        let shard_slug = format!("{}", tenant_shard_id.shard_slug());
        let timeline_id = timeline_id.to_string();
        let global_started = std::array::from_fn(|i| {
            let op = SmgrQueryType::from_repr(i).unwrap();
            SMGR_QUERY_STARTED_GLOBAL
                .get_metric_with_label_values(&[op.into()])
                .unwrap()
        });
        let global_latency = std::array::from_fn(|i| {
            let op = SmgrQueryType::from_repr(i).unwrap();
            SMGR_QUERY_TIME_GLOBAL
                .get_metric_with_label_values(&[op.into()])
                .unwrap()
        });

        let per_timeline_getpage_started = SMGR_QUERY_STARTED_PER_TENANT_TIMELINE
            .get_metric_with_label_values(&[
                SmgrQueryType::GetPageAtLsn.into(),
                &tenant_id,
                &shard_slug,
                &timeline_id,
            ])
            .unwrap();
        let per_timeline_getpage_latency = SMGR_QUERY_TIME_PER_TENANT_TIMELINE
            .get_metric_with_label_values(&[
                SmgrQueryType::GetPageAtLsn.into(),
                &tenant_id,
                &shard_slug,
                &timeline_id,
            ])
            .unwrap();

        let global_batch_size = PAGE_SERVICE_BATCH_SIZE_GLOBAL.clone();
        let per_timeline_batch_size = PAGE_SERVICE_BATCH_SIZE_PER_TENANT_TIMELINE
            .get_metric_with_label_values(&[&tenant_id, &shard_slug, &timeline_id])
            .unwrap();

        let global_batch_wait_time = PAGE_SERVICE_SMGR_BATCH_WAIT_TIME_GLOBAL.clone();
        let per_timeline_batch_wait_time = PAGE_SERVICE_SMGR_BATCH_WAIT_TIME
            .get_metric_with_label_values(&[&tenant_id, &shard_slug, &timeline_id])
            .unwrap();

        let global_batch_break_reason = std::array::from_fn(|i| {
            let reason = GetPageBatchBreakReason::from_usize(i);
            PAGE_SERVICE_BATCH_BREAK_REASON_GLOBAL
                .get_metric_with_label_values(&[reason.into()])
                .unwrap()
        });
        let per_timeline_batch_break_reason =
            GetPageBatchBreakReasonTimelineMetrics::new(&tenant_id, &shard_slug, &timeline_id);

        let global_flush_in_progress_micros =
            PAGE_SERVICE_SMGR_FLUSH_INPROGRESS_MICROS_GLOBAL.clone();
        let per_timeline_flush_in_progress_micros = PAGE_SERVICE_SMGR_FLUSH_INPROGRESS_MICROS
            .get_metric_with_label_values(&[&tenant_id, &shard_slug, &timeline_id])
            .unwrap();

        Self {
            global_started,
            global_latency,
            per_timeline_getpage_latency,
            per_timeline_getpage_started,
            global_batch_size,
            per_timeline_batch_size,
            global_flush_in_progress_micros,
            per_timeline_flush_in_progress_micros,
            global_batch_wait_time,
            per_timeline_batch_wait_time,
            global_batch_break_reason,
            per_timeline_batch_break_reason,
            throttling: pagestream_throttle_metrics,
        }
    }
    pub(crate) fn start_smgr_op(&self, op: SmgrQueryType, received_at: Instant) -> SmgrOpTimer {
        self.global_started[op as usize].inc();

        let per_timeline_latency_histo = if matches!(op, SmgrQueryType::GetPageAtLsn) {
            self.per_timeline_getpage_started.inc();
            Some(self.per_timeline_getpage_latency.clone())
        } else {
            None
        };

        SmgrOpTimer(Some(SmgrOpTimerInner {
            global_execution_latency_histo: self.global_latency[op as usize].clone(),
            per_timeline_execution_latency_histo: per_timeline_latency_histo,
            global_flush_in_progress_micros: self.global_flush_in_progress_micros.clone(),
            per_timeline_flush_in_progress_micros: self
                .per_timeline_flush_in_progress_micros
                .clone(),
            global_batch_wait_time: self.global_batch_wait_time.clone(),
            per_timeline_batch_wait_time: self.per_timeline_batch_wait_time.clone(),
            throttling: self.throttling.clone(),
            timings: SmgrOpTimerState::Received { received_at },
        }))
    }

    /// TODO: do something about this? seems odd, we have a similar call on SmgrOpTimer
    pub(crate) fn observe_getpage_batch_start(
        &self,
        batch_size: usize,
        break_reason: GetPageBatchBreakReason,
    ) {
        self.global_batch_size.observe(batch_size as f64);
        self.per_timeline_batch_size.observe(batch_size as f64);

        self.global_batch_break_reason[break_reason.into_usize()].inc();
        self.per_timeline_batch_break_reason.inc(break_reason);
    }
}

// keep in sync with control plane Go code so that we can validate
// compute's basebackup_ms metric with our perspective in the context of SLI/SLO.
static COMPUTE_STARTUP_BUCKETS: Lazy<[f64; 28]> = Lazy::new(|| {
    // Go code uses milliseconds. Variable is called `computeStartupBuckets`
    [
        5, 10, 20, 30, 50, 70, 100, 120, 150, 200, 250, 300, 350, 400, 450, 500, 600, 800, 1000,
        1500, 2000, 2500, 3000, 5000, 10000, 20000, 40000, 60000,
    ]
    .map(|ms| (ms as f64) / 1000.0)
});

pub(crate) struct BasebackupQueryTime {
    ok: Histogram,
    error: Histogram,
    client_error: Histogram,
}

pub(crate) static BASEBACKUP_QUERY_TIME: Lazy<BasebackupQueryTime> = Lazy::new(|| {
    let vec = register_histogram_vec!(
        "pageserver_basebackup_query_seconds",
        "Histogram of basebackup queries durations, by result type",
        &["result"],
        COMPUTE_STARTUP_BUCKETS.to_vec(),
    )
    .expect("failed to define a metric");
    BasebackupQueryTime {
        ok: vec.get_metric_with_label_values(&["ok"]).unwrap(),
        error: vec.get_metric_with_label_values(&["error"]).unwrap(),
        client_error: vec.get_metric_with_label_values(&["client_error"]).unwrap(),
    }
});

pub(crate) struct BasebackupQueryTimeOngoingRecording<'a> {
    parent: &'a BasebackupQueryTime,
    start: std::time::Instant,
}

impl BasebackupQueryTime {
    pub(crate) fn start_recording(&self) -> BasebackupQueryTimeOngoingRecording<'_> {
        let start = Instant::now();
        BasebackupQueryTimeOngoingRecording {
            parent: self,
            start,
        }
    }
}

impl BasebackupQueryTimeOngoingRecording<'_> {
    pub(crate) fn observe<T>(self, res: &Result<T, QueryError>) {
        let elapsed = self.start.elapsed().as_secs_f64();
        // If you want to change categorize of a specific error, also change it in `log_query_error`.
        let metric = match res {
            Ok(_) => &self.parent.ok,
            Err(QueryError::Disconnected(ConnectionError::Io(io_error)))
                if is_expected_io_error(io_error) =>
            {
                &self.parent.client_error
            }
            Err(_) => &self.parent.error,
        };
        metric.observe(elapsed);
    }
}

pub(crate) static LIVE_CONNECTIONS: Lazy<IntCounterPairVec> = Lazy::new(|| {
    register_int_counter_pair_vec!(
        "pageserver_live_connections_started",
        "Number of network connections that we started handling",
        "pageserver_live_connections_finished",
        "Number of network connections that we finished handling",
        &["pageserver_connection_kind"]
    )
    .expect("failed to define a metric")
});

#[derive(Clone, Copy, enum_map::Enum, IntoStaticStr)]
pub(crate) enum ComputeCommandKind {
    PageStreamV3,
    PageStreamV2,
    Basebackup,
    Fullbackup,
    LeaseLsn,
}

pub(crate) struct ComputeCommandCounters {
    map: EnumMap<ComputeCommandKind, IntCounter>,
}

pub(crate) static COMPUTE_COMMANDS_COUNTERS: Lazy<ComputeCommandCounters> = Lazy::new(|| {
    let inner = register_int_counter_vec!(
        "pageserver_compute_commands",
        "Number of compute -> pageserver commands processed",
        &["command"]
    )
    .expect("failed to define a metric");

    ComputeCommandCounters {
        map: EnumMap::from_array(std::array::from_fn(|i| {
            let command = ComputeCommandKind::from_usize(i);
            let command_str: &'static str = command.into();
            inner.with_label_values(&[command_str])
        })),
    }
});

impl ComputeCommandCounters {
    pub(crate) fn for_command(&self, command: ComputeCommandKind) -> &IntCounter {
        &self.map[command]
    }
}

// remote storage metrics

static REMOTE_TIMELINE_CLIENT_CALLS: Lazy<IntCounterPairVec> = Lazy::new(|| {
    register_int_counter_pair_vec!(
        "pageserver_remote_timeline_client_calls_started",
        "Number of started calls to remote timeline client.",
        "pageserver_remote_timeline_client_calls_finished",
        "Number of finshed calls to remote timeline client.",
        &[
            "tenant_id",
            "shard_id",
            "timeline_id",
            "file_kind",
            "op_kind"
        ],
    )
    .unwrap()
});

static REMOTE_TIMELINE_CLIENT_BYTES_STARTED_COUNTER: Lazy<IntCounterVec> =
    Lazy::new(|| {
        register_int_counter_vec!(
        "pageserver_remote_timeline_client_bytes_started",
        "Incremented by the number of bytes associated with a remote timeline client operation. \
         The increment happens when the operation is scheduled.",
        &["tenant_id", "shard_id", "timeline_id", "file_kind", "op_kind"],
    )
        .expect("failed to define a metric")
    });

static REMOTE_TIMELINE_CLIENT_BYTES_FINISHED_COUNTER: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_remote_timeline_client_bytes_finished",
        "Incremented by the number of bytes associated with a remote timeline client operation. \
         The increment happens when the operation finishes (regardless of success/failure/shutdown).",
        &["tenant_id", "shard_id", "timeline_id", "file_kind", "op_kind"],
    )
    .expect("failed to define a metric")
});

pub(crate) struct TenantManagerMetrics {
    tenant_slots_attached: UIntGauge,
    tenant_slots_secondary: UIntGauge,
    tenant_slots_inprogress: UIntGauge,
    pub(crate) tenant_slot_writes: IntCounter,
    pub(crate) unexpected_errors: IntCounter,
}

impl TenantManagerMetrics {
    /// Helpers for tracking slots.  Note that these do not track the lifetime of TenantSlot objects
    /// exactly: they track the lifetime of the slots _in the tenant map_.
    pub(crate) fn slot_inserted(&self, slot: &TenantSlot) {
        match slot {
            TenantSlot::Attached(_) => {
                self.tenant_slots_attached.inc();
            }
            TenantSlot::Secondary(_) => {
                self.tenant_slots_secondary.inc();
            }
            TenantSlot::InProgress(_) => {
                self.tenant_slots_inprogress.inc();
            }
        }
    }

    pub(crate) fn slot_removed(&self, slot: &TenantSlot) {
        match slot {
            TenantSlot::Attached(_) => {
                self.tenant_slots_attached.dec();
            }
            TenantSlot::Secondary(_) => {
                self.tenant_slots_secondary.dec();
            }
            TenantSlot::InProgress(_) => {
                self.tenant_slots_inprogress.dec();
            }
        }
    }

    #[cfg(all(debug_assertions, not(test)))]
    pub(crate) fn slots_total(&self) -> u64 {
        self.tenant_slots_attached.get()
            + self.tenant_slots_secondary.get()
            + self.tenant_slots_inprogress.get()
    }
}

pub(crate) static TENANT_MANAGER: Lazy<TenantManagerMetrics> = Lazy::new(|| {
    let tenant_slots = register_uint_gauge_vec!(
        "pageserver_tenant_manager_slots",
        "How many slots currently exist, including all attached, secondary and in-progress operations",
        &["mode"]
    )
    .expect("failed to define a metric");
    TenantManagerMetrics {
        tenant_slots_attached: tenant_slots
            .get_metric_with_label_values(&["attached"])
            .unwrap(),
        tenant_slots_secondary: tenant_slots
            .get_metric_with_label_values(&["secondary"])
            .unwrap(),
        tenant_slots_inprogress: tenant_slots
            .get_metric_with_label_values(&["inprogress"])
            .unwrap(),
        tenant_slot_writes: register_int_counter!(
            "pageserver_tenant_manager_slot_writes",
            "Writes to a tenant slot, including all of create/attach/detach/delete"
        )
        .expect("failed to define a metric"),
        unexpected_errors: register_int_counter!(
            "pageserver_tenant_manager_unexpected_errors_total",
            "Number of unexpected conditions encountered: nonzero value indicates a non-fatal bug."
        )
        .expect("failed to define a metric"),
    }
});

pub(crate) struct DeletionQueueMetrics {
    pub(crate) keys_submitted: IntCounter,
    pub(crate) keys_dropped: IntCounter,
    pub(crate) keys_executed: IntCounter,
    pub(crate) keys_validated: IntCounter,
    pub(crate) dropped_lsn_updates: IntCounter,
    pub(crate) unexpected_errors: IntCounter,
    pub(crate) remote_errors: IntCounterVec,
}
pub(crate) static DELETION_QUEUE: Lazy<DeletionQueueMetrics> = Lazy::new(|| {
    DeletionQueueMetrics{

    keys_submitted: register_int_counter!(
        "pageserver_deletion_queue_submitted_total",
        "Number of objects submitted for deletion"
    )
    .expect("failed to define a metric"),

    keys_dropped: register_int_counter!(
        "pageserver_deletion_queue_dropped_total",
        "Number of object deletions dropped due to stale generation."
    )
    .expect("failed to define a metric"),

    keys_executed: register_int_counter!(
        "pageserver_deletion_queue_executed_total",
        "Number of objects deleted. Only includes objects that we actually deleted, sum with pageserver_deletion_queue_dropped_total for the total number of keys processed to completion"
    )
    .expect("failed to define a metric"),

    keys_validated: register_int_counter!(
        "pageserver_deletion_queue_validated_total",
        "Number of keys validated for deletion.  Sum with pageserver_deletion_queue_dropped_total for the total number of keys that have passed through the validation stage."
    )
    .expect("failed to define a metric"),

    dropped_lsn_updates: register_int_counter!(
        "pageserver_deletion_queue_dropped_lsn_updates_total",
        "Updates to remote_consistent_lsn dropped due to stale generation number."
    )
    .expect("failed to define a metric"),
    unexpected_errors: register_int_counter!(
        "pageserver_deletion_queue_unexpected_errors_total",
        "Number of unexpected condiions that may stall the queue: any value above zero is unexpected."
    )
    .expect("failed to define a metric"),
    remote_errors: register_int_counter_vec!(
        "pageserver_deletion_queue_remote_errors_total",
        "Retryable remote I/O errors while executing deletions, for example 503 responses to DeleteObjects",
        &["op_kind"],
    )
    .expect("failed to define a metric")
}
});

pub(crate) struct SecondaryModeMetrics {
    pub(crate) upload_heatmap: IntCounter,
    pub(crate) upload_heatmap_errors: IntCounter,
    pub(crate) upload_heatmap_duration: Histogram,
    pub(crate) download_heatmap: IntCounter,
    pub(crate) download_layer: IntCounter,
}
pub(crate) static SECONDARY_MODE: Lazy<SecondaryModeMetrics> = Lazy::new(|| {
    SecondaryModeMetrics {
    upload_heatmap: register_int_counter!(
        "pageserver_secondary_upload_heatmap",
        "Number of heatmaps written to remote storage by attached tenants"
    )
    .expect("failed to define a metric"),
    upload_heatmap_errors: register_int_counter!(
        "pageserver_secondary_upload_heatmap_errors",
        "Failures writing heatmap to remote storage"
    )
    .expect("failed to define a metric"),
    upload_heatmap_duration: register_histogram!(
        "pageserver_secondary_upload_heatmap_duration",
        "Time to build and upload a heatmap, including any waiting inside the remote storage client"
    )
    .expect("failed to define a metric"),
    download_heatmap: register_int_counter!(
        "pageserver_secondary_download_heatmap",
        "Number of downloads of heatmaps by secondary mode locations, including when it hasn't changed"
    )
    .expect("failed to define a metric"),
    download_layer: register_int_counter!(
        "pageserver_secondary_download_layer",
        "Number of downloads of layers by secondary mode locations"
    )
    .expect("failed to define a metric"),
}
});

pub(crate) static SECONDARY_RESIDENT_PHYSICAL_SIZE: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_secondary_resident_physical_size",
        "The size of the layer files present in the pageserver's filesystem, for secondary locations.",
        &["tenant_id", "shard_id"]
    )
    .expect("failed to define a metric")
});

pub(crate) static NODE_UTILIZATION_SCORE: Lazy<UIntGauge> = Lazy::new(|| {
    register_uint_gauge!(
        "pageserver_utilization_score",
        "The utilization score we report to the storage controller for scheduling, where 0 is empty, 1000000 is full, and anything above is considered overloaded",
    )
    .expect("failed to define a metric")
});

pub(crate) static SECONDARY_HEATMAP_TOTAL_SIZE: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_secondary_heatmap_total_size",
        "The total size in bytes of all layers in the most recently downloaded heatmap.",
        &["tenant_id", "shard_id"]
    )
    .expect("failed to define a metric")
});

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum RemoteOpKind {
    Upload,
    Download,
    Delete,
}
impl RemoteOpKind {
    pub fn as_str(&self) -> &'static str {
        match self {
            Self::Upload => "upload",
            Self::Download => "download",
            Self::Delete => "delete",
        }
    }
}

#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
pub enum RemoteOpFileKind {
    Layer,
    Index,
}
impl RemoteOpFileKind {
    pub fn as_str(&self) -> &'static str {
        match self {
            Self::Layer => "layer",
            Self::Index => "index",
        }
    }
}

pub(crate) static REMOTE_TIMELINE_CLIENT_COMPLETION_LATENCY: Lazy<HistogramVec> = Lazy::new(|| {
    register_histogram_vec!(
        "pageserver_remote_timeline_client_seconds_global",
        "Time spent on remote timeline client operations. \
        Grouped by task_kind, file_kind, operation_kind and status. \
        The task_kind is \
          - for layer downloads, populated from RequestContext (primary objective of having the label) \
          - for index downloads, set to 'unknown' \
          - for any upload operation, set to 'RemoteUploadTask' \
        This keeps dimensionality at bay. \
        Does not account for time spent waiting in remote timeline client's queues.",
        &["task_kind", "file_kind", "op_kind", "status"]
    )
    .expect("failed to define a metric")
});

pub(crate) static TENANT_TASK_EVENTS: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_tenant_task_events",
        "Number of task start/stop/fail events.",
        &["event"],
    )
    .expect("Failed to register tenant_task_events metric")
});

pub struct BackgroundLoopSemaphoreMetrics {
    counters: EnumMap<BackgroundLoopKind, IntCounterPair>,
    durations: EnumMap<BackgroundLoopKind, Histogram>,
    waiting_tasks: EnumMap<BackgroundLoopKind, IntGauge>,
    running_tasks: EnumMap<BackgroundLoopKind, IntGauge>,
}

pub(crate) static BACKGROUND_LOOP_SEMAPHORE: Lazy<BackgroundLoopSemaphoreMetrics> =
    Lazy::new(|| {
        let counters = register_int_counter_pair_vec!(
            "pageserver_background_loop_semaphore_wait_start_count",
            "Counter for background loop concurrency-limiting semaphore acquire calls started",
            "pageserver_background_loop_semaphore_wait_finish_count",
            "Counter for background loop concurrency-limiting semaphore acquire calls finished",
            &["task"],
        )
        .unwrap();

        let durations = register_histogram_vec!(
            "pageserver_background_loop_semaphore_wait_seconds",
            "Seconds spent waiting on background loop semaphore acquisition",
            &["task"],
            vec![0.01, 1.0, 5.0, 10.0, 30.0, 60.0, 180.0, 300.0, 600.0],
        )
        .unwrap();

        let waiting_tasks = register_int_gauge_vec!(
            "pageserver_background_loop_semaphore_waiting_tasks",
            "Number of background loop tasks waiting for semaphore",
            &["task"],
        )
        .unwrap();

        let running_tasks = register_int_gauge_vec!(
            "pageserver_background_loop_semaphore_running_tasks",
            "Number of background loop tasks running concurrently",
            &["task"],
        )
        .unwrap();

        BackgroundLoopSemaphoreMetrics {
            counters: EnumMap::from_array(std::array::from_fn(|i| {
                let kind = BackgroundLoopKind::from_usize(i);
                counters.with_label_values(&[kind.into()])
            })),
            durations: EnumMap::from_array(std::array::from_fn(|i| {
                let kind = BackgroundLoopKind::from_usize(i);
                durations.with_label_values(&[kind.into()])
            })),
            waiting_tasks: EnumMap::from_array(std::array::from_fn(|i| {
                let kind = BackgroundLoopKind::from_usize(i);
                waiting_tasks.with_label_values(&[kind.into()])
            })),
            running_tasks: EnumMap::from_array(std::array::from_fn(|i| {
                let kind = BackgroundLoopKind::from_usize(i);
                running_tasks.with_label_values(&[kind.into()])
            })),
        }
    });

impl BackgroundLoopSemaphoreMetrics {
    /// Starts recording semaphore metrics. Call `acquired()` on the returned recorder when the
    /// semaphore is acquired, and drop it when the task completes or is cancelled.
    pub(crate) fn record(
        &self,
        task: BackgroundLoopKind,
    ) -> BackgroundLoopSemaphoreMetricsRecorder {
        BackgroundLoopSemaphoreMetricsRecorder::start(self, task)
    }
}

/// Records metrics for a background task.
pub struct BackgroundLoopSemaphoreMetricsRecorder<'a> {
    metrics: &'a BackgroundLoopSemaphoreMetrics,
    task: BackgroundLoopKind,
    start: Instant,
    wait_counter_guard: Option<metrics::IntCounterPairGuard>,
}

impl<'a> BackgroundLoopSemaphoreMetricsRecorder<'a> {
    /// Starts recording semaphore metrics, by recording wait time and incrementing
    /// `wait_start_count` and `waiting_tasks`.
    fn start(metrics: &'a BackgroundLoopSemaphoreMetrics, task: BackgroundLoopKind) -> Self {
        metrics.waiting_tasks[task].inc();
        Self {
            metrics,
            task,
            start: Instant::now(),
            wait_counter_guard: Some(metrics.counters[task].guard()),
        }
    }

    /// Signals that the semaphore has been acquired, and updates relevant metrics.
    pub fn acquired(&mut self) -> Duration {
        let waited = self.start.elapsed();
        self.wait_counter_guard.take().expect("already acquired");
        self.metrics.durations[self.task].observe(waited.as_secs_f64());
        self.metrics.waiting_tasks[self.task].dec();
        self.metrics.running_tasks[self.task].inc();
        waited
    }
}

impl Drop for BackgroundLoopSemaphoreMetricsRecorder<'_> {
    /// The task either completed or was cancelled.
    fn drop(&mut self) {
        if self.wait_counter_guard.take().is_some() {
            // Waiting.
            self.metrics.durations[self.task].observe(self.start.elapsed().as_secs_f64());
            self.metrics.waiting_tasks[self.task].dec();
        } else {
            // Running.
            self.metrics.running_tasks[self.task].dec();
        }
    }
}

pub(crate) static BACKGROUND_LOOP_PERIOD_OVERRUN_COUNT: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_background_loop_period_overrun_count",
        "Incremented whenever warn_when_period_overrun() logs a warning.",
        &["task", "period"],
    )
    .expect("failed to define a metric")
});

// walreceiver metrics

pub(crate) static WALRECEIVER_STARTED_CONNECTIONS: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_walreceiver_started_connections_total",
        "Number of started walreceiver connections"
    )
    .expect("failed to define a metric")
});

pub(crate) static WALRECEIVER_ACTIVE_MANAGERS: Lazy<IntGauge> = Lazy::new(|| {
    register_int_gauge!(
        "pageserver_walreceiver_active_managers",
        "Number of active walreceiver managers"
    )
    .expect("failed to define a metric")
});

pub(crate) static WALRECEIVER_SWITCHES: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_walreceiver_switches_total",
        "Number of walreceiver manager change_connection calls",
        &["reason"]
    )
    .expect("failed to define a metric")
});

pub(crate) static WALRECEIVER_BROKER_UPDATES: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_walreceiver_broker_updates_total",
        "Number of received broker updates in walreceiver"
    )
    .expect("failed to define a metric")
});

pub(crate) static WALRECEIVER_CANDIDATES_EVENTS: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_walreceiver_candidates_events_total",
        "Number of walreceiver candidate events",
        &["event"]
    )
    .expect("failed to define a metric")
});

pub(crate) static WALRECEIVER_CANDIDATES_ADDED: Lazy<IntCounter> =
    Lazy::new(|| WALRECEIVER_CANDIDATES_EVENTS.with_label_values(&["add"]));

pub(crate) static WALRECEIVER_CANDIDATES_REMOVED: Lazy<IntCounter> =
    Lazy::new(|| WALRECEIVER_CANDIDATES_EVENTS.with_label_values(&["remove"]));

// Metrics collected on WAL redo operations
//
// We collect the time spent in actual WAL redo ('redo'), and time waiting
// for access to the postgres process ('wait') since there is only one for
// each tenant.

/// Time buckets are small because we want to be able to measure the
/// smallest redo processing times. These buckets allow us to measure down
/// to 5us, which equates to 200'000 pages/sec, which equates to 1.6GB/sec.
/// This is much better than the previous 5ms aka 200 pages/sec aka 1.6MB/sec.
///
/// Values up to 1s are recorded because metrics show that we have redo
/// durations and lock times larger than 0.250s.
macro_rules! redo_histogram_time_buckets {
    () => {
        vec![
            0.000_005, 0.000_010, 0.000_025, 0.000_050, 0.000_100, 0.000_250, 0.000_500, 0.001_000,
            0.002_500, 0.005_000, 0.010_000, 0.025_000, 0.050_000, 0.100_000, 0.250_000, 0.500_000,
            1.000_000,
        ]
    };
}

/// While we're at it, also measure the amount of records replayed in each
/// operation. We have a global 'total replayed' counter, but that's not
/// as useful as 'what is the skew for how many records we replay in one
/// operation'.
macro_rules! redo_histogram_count_buckets {
    () => {
        vec![0.0, 1.0, 2.0, 5.0, 10.0, 25.0, 50.0, 100.0, 250.0, 500.0]
    };
}

macro_rules! redo_bytes_histogram_count_buckets {
    () => {
        // powers of (2^.5), from 2^4.5 to 2^15 (22 buckets)
        // rounded up to the next multiple of 8 to capture any MAXALIGNed record of that size, too.
        vec![
            24.0, 32.0, 48.0, 64.0, 96.0, 128.0, 184.0, 256.0, 368.0, 512.0, 728.0, 1024.0, 1456.0,
            2048.0, 2904.0, 4096.0, 5800.0, 8192.0, 11592.0, 16384.0, 23176.0, 32768.0,
        ]
    };
}

pub(crate) struct WalIngestMetrics {
    pub(crate) bytes_received: IntCounter,
    pub(crate) records_received: IntCounter,
    pub(crate) records_observed: IntCounter,
    pub(crate) records_committed: IntCounter,
    pub(crate) records_filtered: IntCounter,
    pub(crate) values_committed_metadata_images: IntCounter,
    pub(crate) values_committed_metadata_deltas: IntCounter,
    pub(crate) values_committed_data_images: IntCounter,
    pub(crate) values_committed_data_deltas: IntCounter,
    pub(crate) gap_blocks_zeroed_on_rel_extend: IntCounter,
}

impl WalIngestMetrics {
    pub(crate) fn inc_values_committed(&self, stats: &DatadirModificationStats) {
        if stats.metadata_images > 0 {
            self.values_committed_metadata_images
                .inc_by(stats.metadata_images);
        }
        if stats.metadata_deltas > 0 {
            self.values_committed_metadata_deltas
                .inc_by(stats.metadata_deltas);
        }
        if stats.data_images > 0 {
            self.values_committed_data_images.inc_by(stats.data_images);
        }
        if stats.data_deltas > 0 {
            self.values_committed_data_deltas.inc_by(stats.data_deltas);
        }
    }
}

pub(crate) static WAL_INGEST: Lazy<WalIngestMetrics> = Lazy::new(|| {
    let values_committed = register_int_counter_vec!(
        "pageserver_wal_ingest_values_committed",
        "Number of values committed to pageserver storage from WAL records",
        &["class", "kind"],
    )
    .expect("failed to define a metric");

    WalIngestMetrics {
    bytes_received: register_int_counter!(
        "pageserver_wal_ingest_bytes_received",
        "Bytes of WAL ingested from safekeepers",
    )
    .unwrap(),
    records_received: register_int_counter!(
        "pageserver_wal_ingest_records_received",
        "Number of WAL records received from safekeepers"
    )
    .expect("failed to define a metric"),
    records_observed: register_int_counter!(
        "pageserver_wal_ingest_records_observed",
        "Number of WAL records observed from safekeepers. These are metadata only records for shard 0."
    )
    .expect("failed to define a metric"),
    records_committed: register_int_counter!(
        "pageserver_wal_ingest_records_committed",
        "Number of WAL records which resulted in writes to pageserver storage"
    )
    .expect("failed to define a metric"),
    records_filtered: register_int_counter!(
        "pageserver_wal_ingest_records_filtered",
        "Number of WAL records filtered out due to sharding"
    )
    .expect("failed to define a metric"),
    values_committed_metadata_images: values_committed.with_label_values(&["metadata", "image"]),
    values_committed_metadata_deltas: values_committed.with_label_values(&["metadata", "delta"]),
    values_committed_data_images: values_committed.with_label_values(&["data", "image"]),
    values_committed_data_deltas: values_committed.with_label_values(&["data", "delta"]),
    gap_blocks_zeroed_on_rel_extend: register_int_counter!(
        "pageserver_gap_blocks_zeroed_on_rel_extend",
        "Total number of zero gap blocks written on relation extends"
    )
    .expect("failed to define a metric"),
}
});

pub(crate) static PAGESERVER_TIMELINE_WAL_RECORDS_RECEIVED: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_timeline_wal_records_received",
        "Number of WAL records received per shard",
        &["tenant_id", "shard_id", "timeline_id"]
    )
    .expect("failed to define a metric")
});

pub(crate) static WAL_REDO_TIME: Lazy<Histogram> = Lazy::new(|| {
    register_histogram!(
        "pageserver_wal_redo_seconds",
        "Time spent on WAL redo",
        redo_histogram_time_buckets!()
    )
    .expect("failed to define a metric")
});

pub(crate) static WAL_REDO_RECORDS_HISTOGRAM: Lazy<Histogram> = Lazy::new(|| {
    register_histogram!(
        "pageserver_wal_redo_records_histogram",
        "Histogram of number of records replayed per redo in the Postgres WAL redo process",
        redo_histogram_count_buckets!(),
    )
    .expect("failed to define a metric")
});

pub(crate) static WAL_REDO_BYTES_HISTOGRAM: Lazy<Histogram> = Lazy::new(|| {
    register_histogram!(
        "pageserver_wal_redo_bytes_histogram",
        "Histogram of number of records replayed per redo sent to Postgres",
        redo_bytes_histogram_count_buckets!(),
    )
    .expect("failed to define a metric")
});

// FIXME: isn't this already included by WAL_REDO_RECORDS_HISTOGRAM which has _count?
pub(crate) static WAL_REDO_RECORD_COUNTER: Lazy<IntCounter> = Lazy::new(|| {
    register_int_counter!(
        "pageserver_replayed_wal_records_total",
        "Number of WAL records replayed in WAL redo process"
    )
    .unwrap()
});

#[rustfmt::skip]
pub(crate) static WAL_REDO_PROCESS_LAUNCH_DURATION_HISTOGRAM: Lazy<Histogram> = Lazy::new(|| {
    register_histogram!(
        "pageserver_wal_redo_process_launch_duration",
        "Histogram of the duration of successful WalRedoProcess::launch calls",
        vec![
            0.0002, 0.0004, 0.0006, 0.0008, 0.0010,
            0.0020, 0.0040, 0.0060, 0.0080, 0.0100,
            0.0200, 0.0400, 0.0600, 0.0800, 0.1000,
            0.2000, 0.4000, 0.6000, 0.8000, 1.0000,
            1.5000, 2.0000, 2.5000, 3.0000, 4.0000, 10.0000
        ],
    )
    .expect("failed to define a metric")
});

pub(crate) struct WalRedoProcessCounters {
    pub(crate) started: IntCounter,
    pub(crate) killed_by_cause: EnumMap<WalRedoKillCause, IntCounter>,
    pub(crate) active_stderr_logger_tasks_started: IntCounter,
    pub(crate) active_stderr_logger_tasks_finished: IntCounter,
}

#[derive(Debug, enum_map::Enum, strum_macros::IntoStaticStr)]
pub(crate) enum WalRedoKillCause {
    WalRedoProcessDrop,
    NoLeakChildDrop,
    Startup,
}

impl Default for WalRedoProcessCounters {
    fn default() -> Self {
        let started = register_int_counter!(
            "pageserver_wal_redo_process_started_total",
            "Number of WAL redo processes started",
        )
        .unwrap();

        let killed = register_int_counter_vec!(
            "pageserver_wal_redo_process_stopped_total",
            "Number of WAL redo processes stopped",
            &["cause"],
        )
        .unwrap();

        let active_stderr_logger_tasks_started = register_int_counter!(
            "pageserver_walredo_stderr_logger_tasks_started_total",
            "Number of active walredo stderr logger tasks that have started",
        )
        .unwrap();

        let active_stderr_logger_tasks_finished = register_int_counter!(
            "pageserver_walredo_stderr_logger_tasks_finished_total",
            "Number of active walredo stderr logger tasks that have finished",
        )
        .unwrap();

        Self {
            started,
            killed_by_cause: EnumMap::from_array(std::array::from_fn(|i| {
                let cause = WalRedoKillCause::from_usize(i);
                let cause_str: &'static str = cause.into();
                killed.with_label_values(&[cause_str])
            })),
            active_stderr_logger_tasks_started,
            active_stderr_logger_tasks_finished,
        }
    }
}

pub(crate) static WAL_REDO_PROCESS_COUNTERS: Lazy<WalRedoProcessCounters> =
    Lazy::new(WalRedoProcessCounters::default);

/// Similar to `prometheus::HistogramTimer` but does not record on drop.
pub(crate) struct StorageTimeMetricsTimer {
    metrics: StorageTimeMetrics,
    start: Instant,
}

impl StorageTimeMetricsTimer {
    fn new(metrics: StorageTimeMetrics) -> Self {
        Self {
            metrics,
            start: Instant::now(),
        }
    }

    /// Returns the elapsed duration of the timer.
    pub fn elapsed(&self) -> Duration {
        self.start.elapsed()
    }

    /// Record the time from creation to now and return it.
    pub fn stop_and_record(self) -> Duration {
        let duration = self.elapsed();
        let seconds = duration.as_secs_f64();
        self.metrics.timeline_sum.inc_by(seconds);
        self.metrics.timeline_count.inc();
        self.metrics.global_histogram.observe(seconds);
        duration
    }

    /// Turns this timer into a timer, which will always record -- usually this means recording
    /// regardless an early `?` path was taken in a function.
    pub(crate) fn record_on_drop(self) -> AlwaysRecordingStorageTimeMetricsTimer {
        AlwaysRecordingStorageTimeMetricsTimer(Some(self))
    }
}

pub(crate) struct AlwaysRecordingStorageTimeMetricsTimer(Option<StorageTimeMetricsTimer>);

impl Drop for AlwaysRecordingStorageTimeMetricsTimer {
    fn drop(&mut self) {
        if let Some(inner) = self.0.take() {
            inner.stop_and_record();
        }
    }
}

impl AlwaysRecordingStorageTimeMetricsTimer {
    /// Returns the elapsed duration of the timer.
    pub fn elapsed(&self) -> Duration {
        self.0.as_ref().expect("not dropped yet").elapsed()
    }
}

/// Timing facilities for an globally histogrammed metric, which is supported by per tenant and
/// timeline total sum and count.
#[derive(Clone, Debug)]
pub(crate) struct StorageTimeMetrics {
    /// Sum of f64 seconds, per operation, tenant_id and timeline_id
    timeline_sum: Counter,
    /// Number of oeprations, per operation, tenant_id and timeline_id
    timeline_count: IntCounter,
    /// Global histogram having only the "operation" label.
    global_histogram: Histogram,
}

impl StorageTimeMetrics {
    pub fn new(
        operation: StorageTimeOperation,
        tenant_id: &str,
        shard_id: &str,
        timeline_id: &str,
    ) -> Self {
        let operation: &'static str = operation.into();

        let timeline_sum = STORAGE_TIME_SUM_PER_TIMELINE
            .get_metric_with_label_values(&[operation, tenant_id, shard_id, timeline_id])
            .unwrap();
        let timeline_count = STORAGE_TIME_COUNT_PER_TIMELINE
            .get_metric_with_label_values(&[operation, tenant_id, shard_id, timeline_id])
            .unwrap();
        let global_histogram = STORAGE_TIME_GLOBAL
            .get_metric_with_label_values(&[operation])
            .unwrap();

        StorageTimeMetrics {
            timeline_sum,
            timeline_count,
            global_histogram,
        }
    }

    /// Starts timing a new operation.
    ///
    /// Note: unlike `prometheus::HistogramTimer` the returned timer does not record on drop.
    pub fn start_timer(&self) -> StorageTimeMetricsTimer {
        StorageTimeMetricsTimer::new(self.clone())
    }
}

pub(crate) struct TimelineMetrics {
    tenant_id: String,
    shard_id: String,
    timeline_id: String,
    pub flush_time_histo: StorageTimeMetrics,
    pub flush_delay_histo: StorageTimeMetrics,
    pub compact_time_histo: StorageTimeMetrics,
    pub create_images_time_histo: StorageTimeMetrics,
    pub logical_size_histo: StorageTimeMetrics,
    pub imitate_logical_size_histo: StorageTimeMetrics,
    pub load_layer_map_histo: StorageTimeMetrics,
    pub garbage_collect_histo: StorageTimeMetrics,
    pub find_gc_cutoffs_histo: StorageTimeMetrics,
    pub last_record_lsn_gauge: IntGauge,
    pub disk_consistent_lsn_gauge: IntGauge,
    pub pitr_history_size: UIntGauge,
    pub archival_size: UIntGauge,
    pub layers_per_read: Histogram,
    pub standby_horizon_gauge: IntGauge,
    pub resident_physical_size_gauge: UIntGauge,
    pub visible_physical_size_gauge: UIntGauge,
    /// copy of LayeredTimeline.current_logical_size
    pub current_logical_size_gauge: UIntGauge,
    pub aux_file_size_gauge: IntGauge,
    pub directory_entries_count_gauge: Lazy<UIntGauge, Box<dyn Send + Fn() -> UIntGauge>>,
    pub evictions: IntCounter,
    pub evictions_with_low_residence_duration: std::sync::RwLock<EvictionsWithLowResidenceDuration>,
    /// Number of valid LSN leases.
    pub valid_lsn_lease_count_gauge: UIntGauge,
    pub wal_records_received: IntCounter,
    pub storage_io_size: StorageIoSizeMetrics,
    pub wait_lsn_in_progress_micros: GlobalAndPerTenantIntCounter,
    pub wait_lsn_start_finish_counterpair: IntCounterPair,
    pub wait_ondemand_download_time: wait_ondemand_download_time::WaitOndemandDownloadTimeSum,
    shutdown: std::sync::atomic::AtomicBool,
}

impl TimelineMetrics {
    pub fn new(
        tenant_shard_id: &TenantShardId,
        timeline_id_raw: &TimelineId,
        evictions_with_low_residence_duration_builder: EvictionsWithLowResidenceDurationBuilder,
    ) -> Self {
        let tenant_id = tenant_shard_id.tenant_id.to_string();
        let shard_id = format!("{}", tenant_shard_id.shard_slug());
        let timeline_id = timeline_id_raw.to_string();
        let flush_time_histo = StorageTimeMetrics::new(
            StorageTimeOperation::LayerFlush,
            &tenant_id,
            &shard_id,
            &timeline_id,
        );
        let flush_delay_histo = StorageTimeMetrics::new(
            StorageTimeOperation::LayerFlushDelay,
            &tenant_id,
            &shard_id,
            &timeline_id,
        );
        let compact_time_histo = StorageTimeMetrics::new(
            StorageTimeOperation::Compact,
            &tenant_id,
            &shard_id,
            &timeline_id,
        );
        let create_images_time_histo = StorageTimeMetrics::new(
            StorageTimeOperation::CreateImages,
            &tenant_id,
            &shard_id,
            &timeline_id,
        );
        let logical_size_histo = StorageTimeMetrics::new(
            StorageTimeOperation::LogicalSize,
            &tenant_id,
            &shard_id,
            &timeline_id,
        );
        let imitate_logical_size_histo = StorageTimeMetrics::new(
            StorageTimeOperation::ImitateLogicalSize,
            &tenant_id,
            &shard_id,
            &timeline_id,
        );
        let load_layer_map_histo = StorageTimeMetrics::new(
            StorageTimeOperation::LoadLayerMap,
            &tenant_id,
            &shard_id,
            &timeline_id,
        );
        let garbage_collect_histo = StorageTimeMetrics::new(
            StorageTimeOperation::Gc,
            &tenant_id,
            &shard_id,
            &timeline_id,
        );
        let find_gc_cutoffs_histo = StorageTimeMetrics::new(
            StorageTimeOperation::FindGcCutoffs,
            &tenant_id,
            &shard_id,
            &timeline_id,
        );
        let last_record_lsn_gauge = LAST_RECORD_LSN
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();

        let disk_consistent_lsn_gauge = DISK_CONSISTENT_LSN
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();

        let pitr_history_size = PITR_HISTORY_SIZE
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();

        let archival_size = TIMELINE_ARCHIVE_SIZE
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();

        let layers_per_read = LAYERS_PER_READ
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();

        let standby_horizon_gauge = STANDBY_HORIZON
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();
        let resident_physical_size_gauge = RESIDENT_PHYSICAL_SIZE
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();
        let visible_physical_size_gauge = VISIBLE_PHYSICAL_SIZE
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();
        // TODO: we shouldn't expose this metric
        let current_logical_size_gauge = CURRENT_LOGICAL_SIZE
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();
        let aux_file_size_gauge = AUX_FILE_SIZE
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();
        // TODO use impl Trait syntax here once we have ability to use it: https://github.com/rust-lang/rust/issues/63065
        let directory_entries_count_gauge_closure = {
            let tenant_shard_id = *tenant_shard_id;
            let timeline_id_raw = *timeline_id_raw;
            move || {
                let tenant_id = tenant_shard_id.tenant_id.to_string();
                let shard_id = format!("{}", tenant_shard_id.shard_slug());
                let timeline_id = timeline_id_raw.to_string();
                let gauge: UIntGauge = DIRECTORY_ENTRIES_COUNT
                    .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
                    .unwrap();
                gauge
            }
        };
        let directory_entries_count_gauge: Lazy<UIntGauge, Box<dyn Send + Fn() -> UIntGauge>> =
            Lazy::new(Box::new(directory_entries_count_gauge_closure));
        let evictions = EVICTIONS
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();
        let evictions_with_low_residence_duration = evictions_with_low_residence_duration_builder
            .build(&tenant_id, &shard_id, &timeline_id);

        let valid_lsn_lease_count_gauge = VALID_LSN_LEASE_COUNT
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();

        let wal_records_received = PAGESERVER_TIMELINE_WAL_RECORDS_RECEIVED
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();

        let storage_io_size = StorageIoSizeMetrics::new(&tenant_id, &shard_id, &timeline_id);

        let wait_lsn_in_progress_micros = GlobalAndPerTenantIntCounter {
            global: WAIT_LSN_IN_PROGRESS_GLOBAL_MICROS.clone(),
            per_tenant: WAIT_LSN_IN_PROGRESS_MICROS
                .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
                .unwrap(),
        };

        let wait_lsn_start_finish_counterpair = WAIT_LSN_START_FINISH_COUNTERPAIR
            .get_metric_with_label_values(&[&tenant_id, &shard_id, &timeline_id])
            .unwrap();

        let wait_ondemand_download_time =
            wait_ondemand_download_time::WaitOndemandDownloadTimeSum::new(
                &tenant_id,
                &shard_id,
                &timeline_id,
            );

        TimelineMetrics {
            tenant_id,
            shard_id,
            timeline_id,
            flush_time_histo,
            flush_delay_histo,
            compact_time_histo,
            create_images_time_histo,
            logical_size_histo,
            imitate_logical_size_histo,
            garbage_collect_histo,
            find_gc_cutoffs_histo,
            load_layer_map_histo,
            last_record_lsn_gauge,
            disk_consistent_lsn_gauge,
            pitr_history_size,
            archival_size,
            layers_per_read,
            standby_horizon_gauge,
            resident_physical_size_gauge,
            visible_physical_size_gauge,
            current_logical_size_gauge,
            aux_file_size_gauge,
            directory_entries_count_gauge,
            evictions,
            evictions_with_low_residence_duration: std::sync::RwLock::new(
                evictions_with_low_residence_duration,
            ),
            storage_io_size,
            valid_lsn_lease_count_gauge,
            wal_records_received,
            wait_lsn_in_progress_micros,
            wait_lsn_start_finish_counterpair,
            wait_ondemand_download_time,
            shutdown: std::sync::atomic::AtomicBool::default(),
        }
    }

    pub(crate) fn record_new_file_metrics(&self, sz: u64) {
        self.resident_physical_size_add(sz);
    }

    pub(crate) fn resident_physical_size_sub(&self, sz: u64) {
        self.resident_physical_size_gauge.sub(sz);
        crate::metrics::RESIDENT_PHYSICAL_SIZE_GLOBAL.sub(sz);
    }

    pub(crate) fn resident_physical_size_add(&self, sz: u64) {
        self.resident_physical_size_gauge.add(sz);
        crate::metrics::RESIDENT_PHYSICAL_SIZE_GLOBAL.add(sz);
    }

    pub(crate) fn resident_physical_size_get(&self) -> u64 {
        self.resident_physical_size_gauge.get()
    }

    /// Generates TIMELINE_LAYER labels for a persistent layer.
    fn make_layer_labels(&self, layer_desc: &PersistentLayerDesc) -> [&str; 5] {
        let level = match LayerMap::is_l0(&layer_desc.key_range, layer_desc.is_delta()) {
            true => LayerLevel::L0,
            false => LayerLevel::L1,
        };
        let kind = match layer_desc.is_delta() {
            true => LayerKind::Delta,
            false => LayerKind::Image,
        };
        [
            &self.tenant_id,
            &self.shard_id,
            &self.timeline_id,
            level.into(),
            kind.into(),
        ]
    }

    /// Generates TIMELINE_LAYER labels for a frozen ephemeral layer.
    fn make_frozen_layer_labels(&self, _layer: &InMemoryLayer) -> [&str; 5] {
        [
            &self.tenant_id,
            &self.shard_id,
            &self.timeline_id,
            LayerLevel::Frozen.into(),
            LayerKind::Delta.into(), // by definition
        ]
    }

    /// Removes a frozen ephemeral layer to TIMELINE_LAYER metrics.
    pub fn dec_frozen_layer(&self, layer: &InMemoryLayer) {
        assert!(matches!(layer.info(), InMemoryLayerInfo::Frozen { .. }));
        let labels = self.make_frozen_layer_labels(layer);
        let size = layer.try_len().expect("frozen layer should have no writer");
        TIMELINE_LAYER_COUNT
            .get_metric_with_label_values(&labels)
            .unwrap()
            .dec();
        TIMELINE_LAYER_SIZE
            .get_metric_with_label_values(&labels)
            .unwrap()
            .sub(size);
    }

    /// Adds a frozen ephemeral layer to TIMELINE_LAYER metrics.
    pub fn inc_frozen_layer(&self, layer: &InMemoryLayer) {
        assert!(matches!(layer.info(), InMemoryLayerInfo::Frozen { .. }));
        let labels = self.make_frozen_layer_labels(layer);
        let size = layer.try_len().expect("frozen layer should have no writer");
        TIMELINE_LAYER_COUNT
            .get_metric_with_label_values(&labels)
            .unwrap()
            .inc();
        TIMELINE_LAYER_SIZE
            .get_metric_with_label_values(&labels)
            .unwrap()
            .add(size);
    }

    /// Removes a persistent layer from TIMELINE_LAYER metrics.
    pub fn dec_layer(&self, layer_desc: &PersistentLayerDesc) {
        let labels = self.make_layer_labels(layer_desc);
        TIMELINE_LAYER_COUNT
            .get_metric_with_label_values(&labels)
            .unwrap()
            .dec();
        TIMELINE_LAYER_SIZE
            .get_metric_with_label_values(&labels)
            .unwrap()
            .sub(layer_desc.file_size);
    }

    /// Adds a persistent layer to TIMELINE_LAYER metrics.
    pub fn inc_layer(&self, layer_desc: &PersistentLayerDesc) {
        let labels = self.make_layer_labels(layer_desc);
        TIMELINE_LAYER_COUNT
            .get_metric_with_label_values(&labels)
            .unwrap()
            .inc();
        TIMELINE_LAYER_SIZE
            .get_metric_with_label_values(&labels)
            .unwrap()
            .add(layer_desc.file_size);
    }

    pub(crate) fn shutdown(&self) {
        let was_shutdown = self
            .shutdown
            .swap(true, std::sync::atomic::Ordering::Relaxed);

        if was_shutdown {
            // this happens on tenant deletion because tenant first shuts down timelines, then
            // invokes timeline deletion which first shuts down the timeline again.
            // TODO: this can be removed once https://github.com/neondatabase/neon/issues/5080
            return;
        }

        let tenant_id = &self.tenant_id;
        let timeline_id = &self.timeline_id;
        let shard_id = &self.shard_id;
        let _ = LAST_RECORD_LSN.remove_label_values(&[tenant_id, shard_id, timeline_id]);
        let _ = DISK_CONSISTENT_LSN.remove_label_values(&[tenant_id, shard_id, timeline_id]);
        let _ = STANDBY_HORIZON.remove_label_values(&[tenant_id, shard_id, timeline_id]);
        {
            RESIDENT_PHYSICAL_SIZE_GLOBAL.sub(self.resident_physical_size_get());
            let _ = RESIDENT_PHYSICAL_SIZE.remove_label_values(&[tenant_id, shard_id, timeline_id]);
        }
        let _ = VISIBLE_PHYSICAL_SIZE.remove_label_values(&[tenant_id, shard_id, timeline_id]);
        let _ = CURRENT_LOGICAL_SIZE.remove_label_values(&[tenant_id, shard_id, timeline_id]);
        if let Some(metric) = Lazy::get(&DIRECTORY_ENTRIES_COUNT) {
            let _ = metric.remove_label_values(&[tenant_id, shard_id, timeline_id]);
        }

        let _ = TIMELINE_ARCHIVE_SIZE.remove_label_values(&[tenant_id, shard_id, timeline_id]);
        let _ = PITR_HISTORY_SIZE.remove_label_values(&[tenant_id, shard_id, timeline_id]);

        for ref level in LayerLevel::iter() {
            for ref kind in LayerKind::iter() {
                let labels: [&str; 5] =
                    [tenant_id, shard_id, timeline_id, level.into(), kind.into()];
                let _ = TIMELINE_LAYER_SIZE.remove_label_values(&labels);
                let _ = TIMELINE_LAYER_COUNT.remove_label_values(&labels);
            }
        }

        let _ = LAYERS_PER_READ.remove_label_values(&[tenant_id, shard_id, timeline_id]);

        let _ = EVICTIONS.remove_label_values(&[tenant_id, shard_id, timeline_id]);
        let _ = AUX_FILE_SIZE.remove_label_values(&[tenant_id, shard_id, timeline_id]);
        let _ = VALID_LSN_LEASE_COUNT.remove_label_values(&[tenant_id, shard_id, timeline_id]);

        self.evictions_with_low_residence_duration
            .write()
            .unwrap()
            .remove(tenant_id, shard_id, timeline_id);

        // The following metrics are born outside of the TimelineMetrics lifecycle but still
        // removed at the end of it. The idea is to have the metrics outlive the
        // entity during which they're observed, e.g., the smgr metrics shall
        // outlive an individual smgr connection, but not the timeline.

        for op in StorageTimeOperation::VARIANTS {
            let _ = STORAGE_TIME_SUM_PER_TIMELINE.remove_label_values(&[
                op,
                tenant_id,
                shard_id,
                timeline_id,
            ]);
            let _ = STORAGE_TIME_COUNT_PER_TIMELINE.remove_label_values(&[
                op,
                tenant_id,
                shard_id,
                timeline_id,
            ]);
        }

        for op in StorageIoSizeOperation::VARIANTS {
            let _ = STORAGE_IO_SIZE.remove_label_values(&[op, tenant_id, shard_id, timeline_id]);
        }

        let _ =
            WAIT_LSN_IN_PROGRESS_MICROS.remove_label_values(&[tenant_id, shard_id, timeline_id]);

        {
            let mut res = [Ok(()), Ok(())];
            WAIT_LSN_START_FINISH_COUNTERPAIR
                .remove_label_values(&mut res, &[tenant_id, shard_id, timeline_id]);
        }

        wait_ondemand_download_time::shutdown_timeline(tenant_id, shard_id, timeline_id);

        let _ = SMGR_QUERY_STARTED_PER_TENANT_TIMELINE.remove_label_values(&[
            SmgrQueryType::GetPageAtLsn.into(),
            tenant_id,
            shard_id,
            timeline_id,
        ]);
        let _ = SMGR_QUERY_TIME_PER_TENANT_TIMELINE.remove_label_values(&[
            SmgrQueryType::GetPageAtLsn.into(),
            tenant_id,
            shard_id,
            timeline_id,
        ]);
        let _ = PAGE_SERVICE_BATCH_SIZE_PER_TENANT_TIMELINE.remove_label_values(&[
            tenant_id,
            shard_id,
            timeline_id,
        ]);
        let _ = PAGESERVER_TIMELINE_WAL_RECORDS_RECEIVED.remove_label_values(&[
            tenant_id,
            shard_id,
            timeline_id,
        ]);
        let _ = PAGE_SERVICE_SMGR_FLUSH_INPROGRESS_MICROS.remove_label_values(&[
            tenant_id,
            shard_id,
            timeline_id,
        ]);
        let _ = PAGE_SERVICE_SMGR_BATCH_WAIT_TIME.remove_label_values(&[
            tenant_id,
            shard_id,
            timeline_id,
        ]);

        for reason in GetPageBatchBreakReason::iter() {
            let _ = PAGE_SERVICE_BATCH_BREAK_REASON_PER_TENANT_TIMELINE.remove_label_values(&[
                tenant_id,
                shard_id,
                timeline_id,
                reason.into(),
            ]);
        }
    }
}

pub(crate) fn remove_tenant_metrics(tenant_shard_id: &TenantShardId) {
    // Only shard zero deals in synthetic sizes
    if tenant_shard_id.is_shard_zero() {
        let tid = tenant_shard_id.tenant_id.to_string();
        let _ = TENANT_SYNTHETIC_SIZE_METRIC.remove_label_values(&[&tid]);
    }

    tenant_throttling::remove_tenant_metrics(tenant_shard_id);

    // we leave the BROKEN_TENANTS_SET entry if any
}

/// Maintain a per timeline gauge in addition to the global gauge.
pub(crate) struct PerTimelineRemotePhysicalSizeGauge {
    last_set: AtomicU64,
    gauge: UIntGauge,
}

impl PerTimelineRemotePhysicalSizeGauge {
    fn new(per_timeline_gauge: UIntGauge) -> Self {
        Self {
            last_set: AtomicU64::new(0),
            gauge: per_timeline_gauge,
        }
    }
    pub(crate) fn set(&self, sz: u64) {
        self.gauge.set(sz);
        let prev = self.last_set.swap(sz, std::sync::atomic::Ordering::Relaxed);
        if sz < prev {
            REMOTE_PHYSICAL_SIZE_GLOBAL.sub(prev - sz);
        } else {
            REMOTE_PHYSICAL_SIZE_GLOBAL.add(sz - prev);
        };
    }
    pub(crate) fn get(&self) -> u64 {
        self.gauge.get()
    }
}

impl Drop for PerTimelineRemotePhysicalSizeGauge {
    fn drop(&mut self) {
        REMOTE_PHYSICAL_SIZE_GLOBAL.sub(self.last_set.load(std::sync::atomic::Ordering::Relaxed));
    }
}

pub(crate) struct RemoteTimelineClientMetrics {
    tenant_id: String,
    shard_id: String,
    timeline_id: String,
    pub(crate) remote_physical_size_gauge: PerTimelineRemotePhysicalSizeGauge,
    calls: Mutex<HashMap<(&'static str, &'static str), IntCounterPair>>,
    bytes_started_counter: Mutex<HashMap<(&'static str, &'static str), IntCounter>>,
    bytes_finished_counter: Mutex<HashMap<(&'static str, &'static str), IntCounter>>,
    pub(crate) projected_remote_consistent_lsn_gauge: UIntGauge,
}

impl RemoteTimelineClientMetrics {
    pub fn new(tenant_shard_id: &TenantShardId, timeline_id: &TimelineId) -> Self {
        let tenant_id_str = tenant_shard_id.tenant_id.to_string();
        let shard_id_str = format!("{}", tenant_shard_id.shard_slug());
        let timeline_id_str = timeline_id.to_string();

        let remote_physical_size_gauge = PerTimelineRemotePhysicalSizeGauge::new(
            REMOTE_PHYSICAL_SIZE
                .get_metric_with_label_values(&[&tenant_id_str, &shard_id_str, &timeline_id_str])
                .unwrap(),
        );

        let projected_remote_consistent_lsn_gauge = PROJECTED_REMOTE_CONSISTENT_LSN
            .get_metric_with_label_values(&[&tenant_id_str, &shard_id_str, &timeline_id_str])
            .unwrap();

        RemoteTimelineClientMetrics {
            tenant_id: tenant_id_str,
            shard_id: shard_id_str,
            timeline_id: timeline_id_str,
            calls: Mutex::new(HashMap::default()),
            bytes_started_counter: Mutex::new(HashMap::default()),
            bytes_finished_counter: Mutex::new(HashMap::default()),
            remote_physical_size_gauge,
            projected_remote_consistent_lsn_gauge,
        }
    }

    pub fn remote_operation_time(
        &self,
        task_kind: Option<TaskKind>,
        file_kind: &RemoteOpFileKind,
        op_kind: &RemoteOpKind,
        status: &'static str,
    ) -> Histogram {
        REMOTE_TIMELINE_CLIENT_COMPLETION_LATENCY
            .get_metric_with_label_values(&[
                task_kind.as_ref().map(|tk| tk.into()).unwrap_or("unknown"),
                file_kind.as_str(),
                op_kind.as_str(),
                status,
            ])
            .unwrap()
    }

    fn calls_counter_pair(
        &self,
        file_kind: &RemoteOpFileKind,
        op_kind: &RemoteOpKind,
    ) -> IntCounterPair {
        let mut guard = self.calls.lock().unwrap();
        let key = (file_kind.as_str(), op_kind.as_str());
        let metric = guard.entry(key).or_insert_with(move || {
            REMOTE_TIMELINE_CLIENT_CALLS
                .get_metric_with_label_values(&[
                    &self.tenant_id,
                    &self.shard_id,
                    &self.timeline_id,
                    key.0,
                    key.1,
                ])
                .unwrap()
        });
        metric.clone()
    }

    fn bytes_started_counter(
        &self,
        file_kind: &RemoteOpFileKind,
        op_kind: &RemoteOpKind,
    ) -> IntCounter {
        let mut guard = self.bytes_started_counter.lock().unwrap();
        let key = (file_kind.as_str(), op_kind.as_str());
        let metric = guard.entry(key).or_insert_with(move || {
            REMOTE_TIMELINE_CLIENT_BYTES_STARTED_COUNTER
                .get_metric_with_label_values(&[
                    &self.tenant_id,
                    &self.shard_id,
                    &self.timeline_id,
                    key.0,
                    key.1,
                ])
                .unwrap()
        });
        metric.clone()
    }

    fn bytes_finished_counter(
        &self,
        file_kind: &RemoteOpFileKind,
        op_kind: &RemoteOpKind,
    ) -> IntCounter {
        let mut guard = self.bytes_finished_counter.lock().unwrap();
        let key = (file_kind.as_str(), op_kind.as_str());
        let metric = guard.entry(key).or_insert_with(move || {
            REMOTE_TIMELINE_CLIENT_BYTES_FINISHED_COUNTER
                .get_metric_with_label_values(&[
                    &self.tenant_id,
                    &self.shard_id,
                    &self.timeline_id,
                    key.0,
                    key.1,
                ])
                .unwrap()
        });
        metric.clone()
    }
}

#[cfg(test)]
impl RemoteTimelineClientMetrics {
    pub fn get_bytes_started_counter_value(
        &self,
        file_kind: &RemoteOpFileKind,
        op_kind: &RemoteOpKind,
    ) -> Option<u64> {
        let guard = self.bytes_started_counter.lock().unwrap();
        let key = (file_kind.as_str(), op_kind.as_str());
        guard.get(&key).map(|counter| counter.get())
    }

    pub fn get_bytes_finished_counter_value(
        &self,
        file_kind: &RemoteOpFileKind,
        op_kind: &RemoteOpKind,
    ) -> Option<u64> {
        let guard = self.bytes_finished_counter.lock().unwrap();
        let key = (file_kind.as_str(), op_kind.as_str());
        guard.get(&key).map(|counter| counter.get())
    }
}

/// See [`RemoteTimelineClientMetrics::call_begin`].
#[must_use]
pub(crate) struct RemoteTimelineClientCallMetricGuard {
    /// Decremented on drop.
    calls_counter_pair: Option<IntCounterPair>,
    /// If Some(), this references the bytes_finished metric, and we increment it by the given `u64` on drop.
    bytes_finished: Option<(IntCounter, u64)>,
}

impl RemoteTimelineClientCallMetricGuard {
    /// Consume this guard object without performing the metric updates it would do on `drop()`.
    /// The caller vouches to do the metric updates manually.
    pub fn will_decrement_manually(mut self) {
        let RemoteTimelineClientCallMetricGuard {
            calls_counter_pair,
            bytes_finished,
        } = &mut self;
        calls_counter_pair.take();
        bytes_finished.take();
    }
}

impl Drop for RemoteTimelineClientCallMetricGuard {
    fn drop(&mut self) {
        let RemoteTimelineClientCallMetricGuard {
            calls_counter_pair,
            bytes_finished,
        } = self;
        if let Some(guard) = calls_counter_pair.take() {
            guard.dec();
        }
        if let Some((bytes_finished_metric, value)) = bytes_finished {
            bytes_finished_metric.inc_by(*value);
        }
    }
}

/// The enum variants communicate to the [`RemoteTimelineClientMetrics`] whether to
/// track the byte size of this call in applicable metric(s).
pub(crate) enum RemoteTimelineClientMetricsCallTrackSize {
    /// Do not account for this call's byte size in any metrics.
    /// The `reason` field is there to make the call sites self-documenting
    /// about why they don't need the metric.
    DontTrackSize { reason: &'static str },
    /// Track the byte size of the call in applicable metric(s).
    Bytes(u64),
}

impl RemoteTimelineClientMetrics {
    /// Update the metrics that change when a call to the remote timeline client instance starts.
    ///
    /// Drop the returned guard object once the operation is finished to updates corresponding metrics that track completions.
    /// Or, use [`RemoteTimelineClientCallMetricGuard::will_decrement_manually`] and [`call_end`](Self::call_end) if that
    /// is more suitable.
    /// Never do both.
    pub(crate) fn call_begin(
        &self,
        file_kind: &RemoteOpFileKind,
        op_kind: &RemoteOpKind,
        size: RemoteTimelineClientMetricsCallTrackSize,
    ) -> RemoteTimelineClientCallMetricGuard {
        let calls_counter_pair = self.calls_counter_pair(file_kind, op_kind);
        calls_counter_pair.inc();

        let bytes_finished = match size {
            RemoteTimelineClientMetricsCallTrackSize::DontTrackSize { reason: _reason } => {
                // nothing to do
                None
            }
            RemoteTimelineClientMetricsCallTrackSize::Bytes(size) => {
                self.bytes_started_counter(file_kind, op_kind).inc_by(size);
                let finished_counter = self.bytes_finished_counter(file_kind, op_kind);
                Some((finished_counter, size))
            }
        };
        RemoteTimelineClientCallMetricGuard {
            calls_counter_pair: Some(calls_counter_pair),
            bytes_finished,
        }
    }

    /// Manually udpate the metrics that track completions, instead of using the guard object.
    /// Using the guard object is generally preferable.
    /// See [`call_begin`](Self::call_begin) for more context.
    pub(crate) fn call_end(
        &self,
        file_kind: &RemoteOpFileKind,
        op_kind: &RemoteOpKind,
        size: RemoteTimelineClientMetricsCallTrackSize,
    ) {
        let calls_counter_pair = self.calls_counter_pair(file_kind, op_kind);
        calls_counter_pair.dec();
        match size {
            RemoteTimelineClientMetricsCallTrackSize::DontTrackSize { reason: _reason } => {}
            RemoteTimelineClientMetricsCallTrackSize::Bytes(size) => {
                self.bytes_finished_counter(file_kind, op_kind).inc_by(size);
            }
        }
    }
}

impl Drop for RemoteTimelineClientMetrics {
    fn drop(&mut self) {
        let RemoteTimelineClientMetrics {
            tenant_id,
            shard_id,
            timeline_id,
            remote_physical_size_gauge,
            calls,
            bytes_started_counter,
            bytes_finished_counter,
            projected_remote_consistent_lsn_gauge,
        } = self;
        for ((a, b), _) in calls.get_mut().unwrap().drain() {
            let mut res = [Ok(()), Ok(())];
            REMOTE_TIMELINE_CLIENT_CALLS
                .remove_label_values(&mut res, &[tenant_id, shard_id, timeline_id, a, b]);
            // don't care about results
        }
        for ((a, b), _) in bytes_started_counter.get_mut().unwrap().drain() {
            let _ = REMOTE_TIMELINE_CLIENT_BYTES_STARTED_COUNTER.remove_label_values(&[
                tenant_id,
                shard_id,
                timeline_id,
                a,
                b,
            ]);
        }
        for ((a, b), _) in bytes_finished_counter.get_mut().unwrap().drain() {
            let _ = REMOTE_TIMELINE_CLIENT_BYTES_FINISHED_COUNTER.remove_label_values(&[
                tenant_id,
                shard_id,
                timeline_id,
                a,
                b,
            ]);
        }
        {
            let _ = remote_physical_size_gauge; // use to avoid 'unused' warning in desctructuring above
            let _ = REMOTE_PHYSICAL_SIZE.remove_label_values(&[tenant_id, shard_id, timeline_id]);
        }
        {
            let _ = projected_remote_consistent_lsn_gauge;
            let _ = PROJECTED_REMOTE_CONSISTENT_LSN.remove_label_values(&[
                tenant_id,
                shard_id,
                timeline_id,
            ]);
        }
    }
}

/// Wrapper future that measures the time spent by a remote storage operation,
/// and records the time and success/failure as a prometheus metric.
pub(crate) trait MeasureRemoteOp<O, E>: Sized + Future<Output = Result<O, E>> {
    async fn measure_remote_op(
        self,
        task_kind: Option<TaskKind>, // not all caller contexts have a RequestContext / TaskKind handy
        file_kind: RemoteOpFileKind,
        op: RemoteOpKind,
        metrics: Arc<RemoteTimelineClientMetrics>,
    ) -> Result<O, E> {
        let start = Instant::now();
        let res = self.await;
        let duration = start.elapsed();
        let status = if res.is_ok() { &"success" } else { &"failure" };
        metrics
            .remote_operation_time(task_kind, &file_kind, &op, status)
            .observe(duration.as_secs_f64());
        res
    }
}

impl<Fut, O, E> MeasureRemoteOp<O, E> for Fut where Fut: Sized + Future<Output = Result<O, E>> {}

pub mod tokio_epoll_uring {
    use std::collections::HashMap;
    use std::sync::{Arc, Mutex};

    use metrics::{Histogram, LocalHistogram, UIntGauge, register_histogram, register_int_counter};
    use once_cell::sync::Lazy;

    /// Shared storage for tokio-epoll-uring thread local metrics.
    pub(crate) static THREAD_LOCAL_METRICS_STORAGE: Lazy<ThreadLocalMetricsStorage> =
        Lazy::new(|| {
            let slots_submission_queue_depth = register_histogram!(
                "pageserver_tokio_epoll_uring_slots_submission_queue_depth",
                "The slots waiters queue depth of each tokio_epoll_uring system",
                vec![
                    1.0, 2.0, 4.0, 8.0, 16.0, 32.0, 64.0, 128.0, 256.0, 512.0, 1024.0
                ],
            )
            .expect("failed to define a metric");
            ThreadLocalMetricsStorage {
                observers: Mutex::new(HashMap::new()),
                slots_submission_queue_depth,
            }
        });

    pub struct ThreadLocalMetricsStorage {
        /// List of thread local metrics observers.
        observers: Mutex<HashMap<u64, Arc<ThreadLocalMetrics>>>,
        /// A histogram shared between all thread local systems
        /// for collecting slots submission queue depth.
        slots_submission_queue_depth: Histogram,
    }

    /// Each thread-local [`tokio_epoll_uring::System`] gets one of these as its
    /// [`tokio_epoll_uring::metrics::PerSystemMetrics`] generic.
    ///
    /// The System makes observations into [`Self`] and periodically, the collector
    /// comes along and flushes [`Self`] into the shared storage [`THREAD_LOCAL_METRICS_STORAGE`].
    ///
    /// [`LocalHistogram`] is `!Send`, so, we need to put it behind a [`Mutex`].
    /// But except for the periodic flush, the lock is uncontended so there's no waiting
    /// for cache coherence protocol to get an exclusive cache line.
    pub struct ThreadLocalMetrics {
        /// Local observer of thread local tokio-epoll-uring system's slots waiters queue depth.
        slots_submission_queue_depth: Mutex<LocalHistogram>,
    }

    impl ThreadLocalMetricsStorage {
        /// Registers a new thread local system. Returns a thread local metrics observer.
        pub fn register_system(&self, id: u64) -> Arc<ThreadLocalMetrics> {
            let per_system_metrics = Arc::new(ThreadLocalMetrics::new(
                self.slots_submission_queue_depth.local(),
            ));
            let mut g = self.observers.lock().unwrap();
            g.insert(id, Arc::clone(&per_system_metrics));
            per_system_metrics
        }

        /// Removes metrics observer for a thread local system.
        /// This should be called before dropping a thread local system.
        pub fn remove_system(&self, id: u64) {
            let mut g = self.observers.lock().unwrap();
            g.remove(&id);
        }

        /// Flush all thread local metrics to the shared storage.
        pub fn flush_thread_local_metrics(&self) {
            let g = self.observers.lock().unwrap();
            g.values().for_each(|local| {
                local.flush();
            });
        }
    }

    impl ThreadLocalMetrics {
        pub fn new(slots_submission_queue_depth: LocalHistogram) -> Self {
            ThreadLocalMetrics {
                slots_submission_queue_depth: Mutex::new(slots_submission_queue_depth),
            }
        }

        /// Flushes the thread local metrics to shared aggregator.
        pub fn flush(&self) {
            let Self {
                slots_submission_queue_depth,
            } = self;
            slots_submission_queue_depth.lock().unwrap().flush();
        }
    }

    impl tokio_epoll_uring::metrics::PerSystemMetrics for ThreadLocalMetrics {
        fn observe_slots_submission_queue_depth(&self, queue_depth: u64) {
            let Self {
                slots_submission_queue_depth,
            } = self;
            slots_submission_queue_depth
                .lock()
                .unwrap()
                .observe(queue_depth as f64);
        }
    }

    pub struct Collector {
        descs: Vec<metrics::core::Desc>,
        systems_created: UIntGauge,
        systems_destroyed: UIntGauge,
        thread_local_metrics_storage: &'static ThreadLocalMetricsStorage,
    }

    impl metrics::core::Collector for Collector {
        fn desc(&self) -> Vec<&metrics::core::Desc> {
            self.descs.iter().collect()
        }

        fn collect(&self) -> Vec<metrics::proto::MetricFamily> {
            let mut mfs = Vec::with_capacity(Self::NMETRICS);
            let tokio_epoll_uring::metrics::GlobalMetrics {
                systems_created,
                systems_destroyed,
            } = tokio_epoll_uring::metrics::global();
            self.systems_created.set(systems_created);
            mfs.extend(self.systems_created.collect());
            self.systems_destroyed.set(systems_destroyed);
            mfs.extend(self.systems_destroyed.collect());

            self.thread_local_metrics_storage
                .flush_thread_local_metrics();

            mfs.extend(
                self.thread_local_metrics_storage
                    .slots_submission_queue_depth
                    .collect(),
            );
            mfs
        }
    }

    impl Collector {
        const NMETRICS: usize = 3;

        #[allow(clippy::new_without_default)]
        pub fn new() -> Self {
            let mut descs = Vec::new();

            let systems_created = UIntGauge::new(
                "pageserver_tokio_epoll_uring_systems_created",
                "counter of tokio-epoll-uring systems that were created",
            )
            .unwrap();
            descs.extend(
                metrics::core::Collector::desc(&systems_created)
                    .into_iter()
                    .cloned(),
            );

            let systems_destroyed = UIntGauge::new(
                "pageserver_tokio_epoll_uring_systems_destroyed",
                "counter of tokio-epoll-uring systems that were destroyed",
            )
            .unwrap();
            descs.extend(
                metrics::core::Collector::desc(&systems_destroyed)
                    .into_iter()
                    .cloned(),
            );

            Self {
                descs,
                systems_created,
                systems_destroyed,
                thread_local_metrics_storage: &THREAD_LOCAL_METRICS_STORAGE,
            }
        }
    }

    pub(crate) static THREAD_LOCAL_LAUNCH_SUCCESSES: Lazy<metrics::IntCounter> = Lazy::new(|| {
        register_int_counter!(
            "pageserver_tokio_epoll_uring_pageserver_thread_local_launch_success_count",
            "Number of times where thread_local_system creation spanned multiple executor threads",
        )
        .unwrap()
    });

    pub(crate) static THREAD_LOCAL_LAUNCH_FAILURES: Lazy<metrics::IntCounter> = Lazy::new(|| {
        register_int_counter!(
            "pageserver_tokio_epoll_uring_pageserver_thread_local_launch_failures_count",
            "Number of times thread_local_system creation failed and was retried after back-off.",
        )
        .unwrap()
    });
}

pub(crate) struct GlobalAndPerTenantIntCounter {
    global: IntCounter,
    per_tenant: IntCounter,
}

impl GlobalAndPerTenantIntCounter {
    #[inline(always)]
    pub(crate) fn inc(&self) {
        self.inc_by(1)
    }
    #[inline(always)]
    pub(crate) fn inc_by(&self, n: u64) {
        self.global.inc_by(n);
        self.per_tenant.inc_by(n);
    }
}

pub(crate) mod tenant_throttling {
    use metrics::register_int_counter_vec;
    use once_cell::sync::Lazy;
    use utils::shard::TenantShardId;

    use super::GlobalAndPerTenantIntCounter;

    pub(crate) struct Metrics<const KIND: usize> {
        pub(super) count_accounted_start: GlobalAndPerTenantIntCounter,
        pub(super) count_accounted_finish: GlobalAndPerTenantIntCounter,
        pub(super) wait_time: GlobalAndPerTenantIntCounter,
        pub(super) count_throttled: GlobalAndPerTenantIntCounter,
    }

    static COUNT_ACCOUNTED_START: Lazy<metrics::IntCounterVec> = Lazy::new(|| {
        register_int_counter_vec!(
            "pageserver_tenant_throttling_count_accounted_start_global",
            "Count of tenant throttling starts, by kind of throttle.",
            &["kind"]
        )
        .unwrap()
    });
    static COUNT_ACCOUNTED_START_PER_TENANT: Lazy<metrics::IntCounterVec> = Lazy::new(|| {
        register_int_counter_vec!(
            "pageserver_tenant_throttling_count_accounted_start",
            "Count of tenant throttling starts, by kind of throttle.",
            &["kind", "tenant_id", "shard_id"]
        )
        .unwrap()
    });
    static COUNT_ACCOUNTED_FINISH: Lazy<metrics::IntCounterVec> = Lazy::new(|| {
        register_int_counter_vec!(
            "pageserver_tenant_throttling_count_accounted_finish_global",
            "Count of tenant throttling finishes, by kind of throttle.",
            &["kind"]
        )
        .unwrap()
    });
    static COUNT_ACCOUNTED_FINISH_PER_TENANT: Lazy<metrics::IntCounterVec> = Lazy::new(|| {
        register_int_counter_vec!(
            "pageserver_tenant_throttling_count_accounted_finish",
            "Count of tenant throttling finishes, by kind of throttle.",
            &["kind", "tenant_id", "shard_id"]
        )
        .unwrap()
    });
    static WAIT_USECS: Lazy<metrics::IntCounterVec> = Lazy::new(|| {
        register_int_counter_vec!(
            "pageserver_tenant_throttling_wait_usecs_sum_global",
            "Sum of microseconds that spent waiting throttle by kind of throttle.",
            &["kind"]
        )
        .unwrap()
    });
    static WAIT_USECS_PER_TENANT: Lazy<metrics::IntCounterVec> = Lazy::new(|| {
        register_int_counter_vec!(
            "pageserver_tenant_throttling_wait_usecs_sum",
            "Sum of microseconds that spent waiting throttle by kind of throttle.",
            &["kind", "tenant_id", "shard_id"]
        )
        .unwrap()
    });

    static WAIT_COUNT: Lazy<metrics::IntCounterVec> = Lazy::new(|| {
        register_int_counter_vec!(
            "pageserver_tenant_throttling_count_global",
            "Count of tenant throttlings, by kind of throttle.",
            &["kind"]
        )
        .unwrap()
    });
    static WAIT_COUNT_PER_TENANT: Lazy<metrics::IntCounterVec> = Lazy::new(|| {
        register_int_counter_vec!(
            "pageserver_tenant_throttling_count",
            "Count of tenant throttlings, by kind of throttle.",
            &["kind", "tenant_id", "shard_id"]
        )
        .unwrap()
    });

    const KINDS: &[&str] = &["pagestream"];
    pub type Pagestream = Metrics<0>;

    impl<const KIND: usize> Metrics<KIND> {
        pub(crate) fn new(tenant_shard_id: &TenantShardId) -> Self {
            let per_tenant_label_values = &[
                KINDS[KIND],
                &tenant_shard_id.tenant_id.to_string(),
                &tenant_shard_id.shard_slug().to_string(),
            ];
            Metrics {
                count_accounted_start: {
                    GlobalAndPerTenantIntCounter {
                        global: COUNT_ACCOUNTED_START.with_label_values(&[KINDS[KIND]]),
                        per_tenant: COUNT_ACCOUNTED_START_PER_TENANT
                            .with_label_values(per_tenant_label_values),
                    }
                },
                count_accounted_finish: {
                    GlobalAndPerTenantIntCounter {
                        global: COUNT_ACCOUNTED_FINISH.with_label_values(&[KINDS[KIND]]),
                        per_tenant: COUNT_ACCOUNTED_FINISH_PER_TENANT
                            .with_label_values(per_tenant_label_values),
                    }
                },
                wait_time: {
                    GlobalAndPerTenantIntCounter {
                        global: WAIT_USECS.with_label_values(&[KINDS[KIND]]),
                        per_tenant: WAIT_USECS_PER_TENANT
                            .with_label_values(per_tenant_label_values),
                    }
                },
                count_throttled: {
                    GlobalAndPerTenantIntCounter {
                        global: WAIT_COUNT.with_label_values(&[KINDS[KIND]]),
                        per_tenant: WAIT_COUNT_PER_TENANT
                            .with_label_values(per_tenant_label_values),
                    }
                },
            }
        }
    }

    pub(crate) fn preinitialize_global_metrics() {
        Lazy::force(&COUNT_ACCOUNTED_START);
        Lazy::force(&COUNT_ACCOUNTED_FINISH);
        Lazy::force(&WAIT_USECS);
        Lazy::force(&WAIT_COUNT);
    }

    pub(crate) fn remove_tenant_metrics(tenant_shard_id: &TenantShardId) {
        for m in &[
            &COUNT_ACCOUNTED_START_PER_TENANT,
            &COUNT_ACCOUNTED_FINISH_PER_TENANT,
            &WAIT_USECS_PER_TENANT,
            &WAIT_COUNT_PER_TENANT,
        ] {
            for kind in KINDS {
                let _ = m.remove_label_values(&[
                    kind,
                    &tenant_shard_id.tenant_id.to_string(),
                    &tenant_shard_id.shard_slug().to_string(),
                ]);
            }
        }
    }
}

pub(crate) mod disk_usage_based_eviction {
    use super::*;

    pub(crate) struct Metrics {
        pub(crate) tenant_collection_time: Histogram,
        pub(crate) tenant_layer_count: Histogram,
        pub(crate) layers_collected: IntCounter,
        pub(crate) layers_selected: IntCounter,
        pub(crate) layers_evicted: IntCounter,
    }

    impl Default for Metrics {
        fn default() -> Self {
            let tenant_collection_time = register_histogram!(
                "pageserver_disk_usage_based_eviction_tenant_collection_seconds",
                "Time spent collecting layers from a tenant -- not normalized by collected layer amount",
                vec![0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1.0, 5.0, 10.0]
            )
            .unwrap();

            let tenant_layer_count = register_histogram!(
                "pageserver_disk_usage_based_eviction_tenant_collected_layers",
                "Amount of layers gathered from a tenant",
                vec![5.0, 50.0, 500.0, 5000.0, 50000.0]
            )
            .unwrap();

            let layers_collected = register_int_counter!(
                "pageserver_disk_usage_based_eviction_collected_layers_total",
                "Amount of layers collected"
            )
            .unwrap();

            let layers_selected = register_int_counter!(
                "pageserver_disk_usage_based_eviction_select_layers_total",
                "Amount of layers selected"
            )
            .unwrap();

            let layers_evicted = register_int_counter!(
                "pageserver_disk_usage_based_eviction_evicted_layers_total",
                "Amount of layers successfully evicted"
            )
            .unwrap();

            Self {
                tenant_collection_time,
                tenant_layer_count,
                layers_collected,
                layers_selected,
                layers_evicted,
            }
        }
    }

    pub(crate) static METRICS: Lazy<Metrics> = Lazy::new(Metrics::default);
}

static TOKIO_EXECUTOR_THREAD_COUNT: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_tokio_executor_thread_configured_count",
        "Total number of configued tokio executor threads in the process.
         The `setup` label denotes whether we're running with multiple runtimes or a single runtime.",
        &["setup"],
    )
    .unwrap()
});

pub(crate) fn set_tokio_runtime_setup(setup: &str, num_threads: NonZeroUsize) {
    static SERIALIZE: std::sync::Mutex<()> = std::sync::Mutex::new(());
    let _guard = SERIALIZE.lock().unwrap();
    TOKIO_EXECUTOR_THREAD_COUNT.reset();
    TOKIO_EXECUTOR_THREAD_COUNT
        .get_metric_with_label_values(&[setup])
        .unwrap()
        .set(u64::try_from(num_threads.get()).unwrap());
}

static PAGESERVER_CONFIG_IGNORED_ITEMS: Lazy<UIntGaugeVec> = Lazy::new(|| {
    register_uint_gauge_vec!(
        "pageserver_config_ignored_items",
        "TOML items present in the on-disk configuration file but ignored by the pageserver config parser.\
         The `item` label is the dot-separated path of the ignored item in the on-disk configuration file.\
         The value for an unknown config item is always 1.\
         There is a special label value \"\", which is 0, so that there is always a metric exposed (simplifies dashboards).",
        &["item"]
    )
    .unwrap()
});

pub fn preinitialize_metrics(
    conf: &'static PageServerConf,
    ignored: config::ignored_fields::Paths,
) {
    set_page_service_config_max_batch_size(&conf.page_service_pipelining);

    PAGESERVER_CONFIG_IGNORED_ITEMS
        .with_label_values(&[""])
        .set(0);
    for path in &ignored.paths {
        PAGESERVER_CONFIG_IGNORED_ITEMS
            .with_label_values(&[path])
            .set(1);
    }

    // Python tests need these and on some we do alerting.
    //
    // FIXME(4813): make it so that we have no top level metrics as this fn will easily fall out of
    // order:
    // - global metrics reside in a Lazy<PageserverMetrics>
    //   - access via crate::metrics::PS_METRICS.some_metric.inc()
    // - could move the statics into TimelineMetrics::new()?

    // counters
    [
        &UNEXPECTED_ONDEMAND_DOWNLOADS,
        &WALRECEIVER_STARTED_CONNECTIONS,
        &WALRECEIVER_BROKER_UPDATES,
        &WALRECEIVER_CANDIDATES_ADDED,
        &WALRECEIVER_CANDIDATES_REMOVED,
        &tokio_epoll_uring::THREAD_LOCAL_LAUNCH_FAILURES,
        &tokio_epoll_uring::THREAD_LOCAL_LAUNCH_SUCCESSES,
        &REMOTE_ONDEMAND_DOWNLOADED_LAYERS,
        &REMOTE_ONDEMAND_DOWNLOADED_BYTES,
        &CIRCUIT_BREAKERS_BROKEN,
        &CIRCUIT_BREAKERS_UNBROKEN,
        &PAGE_SERVICE_SMGR_FLUSH_INPROGRESS_MICROS_GLOBAL,
        &WAIT_LSN_IN_PROGRESS_GLOBAL_MICROS,
    ]
    .into_iter()
    .for_each(|c| {
        Lazy::force(c);
    });

    // Deletion queue stats
    Lazy::force(&DELETION_QUEUE);

    // Tenant stats
    Lazy::force(&TENANT);

    // Tenant manager stats
    Lazy::force(&TENANT_MANAGER);

    Lazy::force(&crate::tenant::storage_layer::layer::LAYER_IMPL_METRICS);
    Lazy::force(&disk_usage_based_eviction::METRICS);

    for state_name in pageserver_api::models::TenantState::VARIANTS {
        // initialize the metric for all gauges, otherwise the time series might seemingly show
        // values from last restart.
        TENANT_STATE_METRIC.with_label_values(&[state_name]).set(0);
    }

    // countervecs
    [
        &BACKGROUND_LOOP_PERIOD_OVERRUN_COUNT,
        &SMGR_QUERY_STARTED_GLOBAL,
        &PAGE_SERVICE_BATCH_BREAK_REASON_GLOBAL,
    ]
    .into_iter()
    .for_each(|c| {
        Lazy::force(c);
    });

    // gauges
    WALRECEIVER_ACTIVE_MANAGERS.get();

    // histograms
    [
        &LAYERS_PER_READ_GLOBAL,
        &LAYERS_PER_READ_BATCH_GLOBAL,
        &LAYERS_PER_READ_AMORTIZED_GLOBAL,
        &DELTAS_PER_READ_GLOBAL,
        &WAIT_LSN_TIME,
        &WAL_REDO_TIME,
        &WAL_REDO_RECORDS_HISTOGRAM,
        &WAL_REDO_BYTES_HISTOGRAM,
        &WAL_REDO_PROCESS_LAUNCH_DURATION_HISTOGRAM,
        &PAGE_SERVICE_BATCH_SIZE_GLOBAL,
        &PAGE_SERVICE_SMGR_BATCH_WAIT_TIME_GLOBAL,
    ]
    .into_iter()
    .for_each(|h| {
        Lazy::force(h);
    });

    // Custom
    Lazy::force(&BASEBACKUP_QUERY_TIME);
    Lazy::force(&COMPUTE_COMMANDS_COUNTERS);
    Lazy::force(&tokio_epoll_uring::THREAD_LOCAL_METRICS_STORAGE);

    tenant_throttling::preinitialize_global_metrics();
    wait_ondemand_download_time::preinitialize_global_metrics();
}