Merge remote-tracking branch 'origin/problame/benchmarking/pr/mgmt-api-client' into problame/benchmarking/pr/keyspace-in-mgmt-api

pageserver/src/bin/pageserver.rs

@@ -14,7 +14,7 @@ use pageserver::control_plane_client::ControlPlaneClient;
 use pageserver::disk_usage_eviction_task::{self, launch_disk_usage_global_eviction_task};
 use pageserver::metrics::{STARTUP_DURATION, STARTUP_IS_LOADING};
 use pageserver::task_mgr::WALRECEIVER_RUNTIME;
-use pageserver::tenant::TenantSharedResources;
+use pageserver::tenant::{secondary, TenantSharedResources};
 use remote_storage::GenericRemoteStorage;
 use tokio::time::Instant;
 use tracing::*;
@@ -504,6 +504,17 @@ fn start_pageserver(
         }
     });
 
+    let secondary_controller = if let Some(remote_storage) = &remote_storage {
+        secondary::spawn_tasks(
+            tenant_manager.clone(),
+            remote_storage.clone(),
+            background_jobs_barrier.clone(),
+            shutdown_pageserver.clone(),
+        )
+    } else {
+        secondary::null_controller()
+    };
+
     // shared state between the disk-usage backed eviction background task and the http endpoint
     // that allows triggering disk-usage based eviction manually. note that the http endpoint
     // is still accessible even if background task is not configured as long as remote storage has
@@ -533,6 +544,7 @@ fn start_pageserver(
                 broker_client.clone(),
                 disk_usage_eviction_state,
                 deletion_queue.new_client(),
+                secondary_controller,
             )
             .context("Failed to initialize router state")?,
         );

pageserver/src/config.rs

@@ -70,6 +70,8 @@ pub mod defaults {
     pub const DEFAULT_SYNTHETIC_SIZE_CALCULATION_INTERVAL: &str = "10 min";
     pub const DEFAULT_BACKGROUND_TASK_MAXIMUM_DELAY: &str = "10s";
 
+    pub const DEFAULT_HEATMAP_UPLOAD_CONCURRENCY: usize = 8;
+
     ///
     /// Default built-in configuration file.
     ///
@@ -117,6 +119,8 @@ pub mod defaults {
 #evictions_low_residence_duration_metric_threshold = '{DEFAULT_EVICTIONS_LOW_RESIDENCE_DURATION_METRIC_THRESHOLD}'
 #gc_feedback = false
 
+#heatmap_upload_concurrency = {DEFAULT_HEATMAP_UPLOAD_CONCURRENCY}
+
 [remote_storage]
 
 "#
@@ -215,6 +219,10 @@ pub struct PageServerConf {
     /// If true, pageserver will make best-effort to operate without a control plane: only
     /// for use in major incidents.
     pub control_plane_emergency_mode: bool,
+
+    /// How many heatmap uploads may be done concurrency: lower values implicitly deprioritize
+    /// heatmap uploads vs. other remote storage operations.
+    pub heatmap_upload_concurrency: usize,
 }
 
 /// We do not want to store this in a PageServerConf because the latter may be logged
@@ -293,6 +301,8 @@ struct PageServerConfigBuilder {
     control_plane_api: BuilderValue<Option<Url>>,
     control_plane_api_token: BuilderValue<Option<SecretString>>,
     control_plane_emergency_mode: BuilderValue<bool>,
+
+    heatmap_upload_concurrency: BuilderValue<usize>,
 }
 
 impl Default for PageServerConfigBuilder {
@@ -361,6 +371,8 @@ impl Default for PageServerConfigBuilder {
             control_plane_api: Set(None),
             control_plane_api_token: Set(None),
             control_plane_emergency_mode: Set(false),
+
+            heatmap_upload_concurrency: Set(DEFAULT_HEATMAP_UPLOAD_CONCURRENCY),
         }
     }
 }
@@ -501,6 +513,10 @@ impl PageServerConfigBuilder {
         self.control_plane_emergency_mode = BuilderValue::Set(enabled)
     }
 
+    pub fn heatmap_upload_concurrency(&mut self, value: usize) {
+        self.heatmap_upload_concurrency = BuilderValue::Set(value)
+    }
+
     pub fn build(self) -> anyhow::Result<PageServerConf> {
         let concurrent_tenant_size_logical_size_queries = self
             .concurrent_tenant_size_logical_size_queries
@@ -595,6 +611,10 @@ impl PageServerConfigBuilder {
             control_plane_emergency_mode: self
                 .control_plane_emergency_mode
                 .ok_or(anyhow!("missing control_plane_emergency_mode"))?,
+
+            heatmap_upload_concurrency: self
+                .heatmap_upload_concurrency
+                .ok_or(anyhow!("missing heatmap_upload_concurrency"))?,
         })
     }
 }
@@ -828,7 +848,9 @@ impl PageServerConf {
                 },
                 "control_plane_emergency_mode" => {
                     builder.control_plane_emergency_mode(parse_toml_bool(key, item)?)
-
+                },
+                "heatmap_upload_concurrency" => {
+                    builder.heatmap_upload_concurrency(parse_toml_u64(key, item)? as usize)
                 },
                 _ => bail!("unrecognized pageserver option '{key}'"),
             }
@@ -896,6 +918,7 @@ impl PageServerConf {
             control_plane_api: None,
             control_plane_api_token: None,
             control_plane_emergency_mode: false,
+            heatmap_upload_concurrency: defaults::DEFAULT_HEATMAP_UPLOAD_CONCURRENCY,
         }
     }
 }
@@ -1120,7 +1143,8 @@ background_task_maximum_delay = '334 s'
                 )?,
                 control_plane_api: None,
                 control_plane_api_token: None,
-                control_plane_emergency_mode: false
+                control_plane_emergency_mode: false,
+                heatmap_upload_concurrency: defaults::DEFAULT_HEATMAP_UPLOAD_CONCURRENCY
             },
             "Correct defaults should be used when no config values are provided"
         );
@@ -1177,7 +1201,8 @@ background_task_maximum_delay = '334 s'
                 background_task_maximum_delay: Duration::from_secs(334),
                 control_plane_api: None,
                 control_plane_api_token: None,
-                control_plane_emergency_mode: false
+                control_plane_emergency_mode: false,
+                heatmap_upload_concurrency: defaults::DEFAULT_HEATMAP_UPLOAD_CONCURRENCY
             },
             "Should be able to parse all basic config values correctly"
         );

pageserver/src/consumption_metrics.rs

@@ -3,7 +3,7 @@
 use crate::context::{DownloadBehavior, RequestContext};
 use crate::task_mgr::{self, TaskKind, BACKGROUND_RUNTIME};
 use crate::tenant::tasks::BackgroundLoopKind;
-use crate::tenant::{mgr, LogicalSizeCalculationCause, PageReconstructError};
+use crate::tenant::{mgr, LogicalSizeCalculationCause, PageReconstructError, Tenant};
 use camino::Utf8PathBuf;
 use consumption_metrics::EventType;
 use pageserver_api::models::TenantState;
@@ -256,8 +256,6 @@ async fn calculate_synthetic_size_worker(
         info!("calculate_synthetic_size_worker stopped");
     };
 
-    let cause = LogicalSizeCalculationCause::ConsumptionMetricsSyntheticSize;
-
     loop {
         let started_at = Instant::now();
 
@@ -280,29 +278,14 @@ async fn calculate_synthetic_size_worker(
                 continue;
             }
 
-            if let Ok(tenant) = mgr::get_tenant(tenant_shard_id, true) {
-                // TODO should we use concurrent_background_tasks_rate_limit() here, like the other background tasks?
-                // We can put in some prioritization for consumption metrics.
-                // Same for the loop that fetches computed metrics.
-                // By using the same limiter, we centralize metrics collection for "start" and "finished" counters,
-                // which turns out is really handy to understand the system.
-                if let Err(e) = tenant.calculate_synthetic_size(cause, cancel, ctx).await {
-                    // this error can be returned if timeline is shutting down, but it does not
-                    // mean the synthetic size worker should terminate. we do not need any checks
-                    // in this function because `mgr::get_tenant` will error out after shutdown has
-                    // progressed to shutting down tenants.
-                    let is_cancelled = matches!(
-                        e.downcast_ref::<PageReconstructError>(),
-                        Some(PageReconstructError::Cancelled)
-                    );
+            let Ok(tenant) = mgr::get_tenant(tenant_shard_id, true) else {
+                continue;
+            };
 
-                    if !is_cancelled {
-                        error!(
-                            "failed to calculate synthetic size for tenant {tenant_shard_id}: {e:#}"
-                        );
-                    }
-                }
-            }
+            // there is never any reason to exit calculate_synthetic_size_worker following any
+            // return value -- we don't need to care about shutdown because no tenant is found when
+            // pageserver is shut down.
+            calculate_and_log(&tenant, cancel, ctx).await;
         }
 
         crate::tenant::tasks::warn_when_period_overrun(
@@ -321,3 +304,31 @@ async fn calculate_synthetic_size_worker(
         }
     }
 }
+
+async fn calculate_and_log(tenant: &Tenant, cancel: &CancellationToken, ctx: &RequestContext) {
+    const CAUSE: LogicalSizeCalculationCause =
+        LogicalSizeCalculationCause::ConsumptionMetricsSyntheticSize;
+
+    // TODO should we use concurrent_background_tasks_rate_limit() here, like the other background tasks?
+    // We can put in some prioritization for consumption metrics.
+    // Same for the loop that fetches computed metrics.
+    // By using the same limiter, we centralize metrics collection for "start" and "finished" counters,
+    // which turns out is really handy to understand the system.
+    let Err(e) = tenant.calculate_synthetic_size(CAUSE, cancel, ctx).await else {
+        return;
+    };
+
+    // this error can be returned if timeline is shutting down, but it does not
+    // mean the synthetic size worker should terminate. we do not need any checks
+    // in this function because `mgr::get_tenant` will error out after shutdown has
+    // progressed to shutting down tenants.
+    let shutting_down = matches!(
+        e.downcast_ref::<PageReconstructError>(),
+        Some(PageReconstructError::Cancelled | PageReconstructError::AncestorStopping(_))
+    );
+
+    if !shutting_down {
+        let tenant_shard_id = tenant.tenant_shard_id();
+        error!("failed to calculate synthetic size for tenant {tenant_shard_id}: {e:#}");
+    }
+}

pageserver/src/disk_usage_eviction_task.rs

@@ -42,7 +42,6 @@
 //   reading these fields. We use the Debug impl for semi-structured logging, though.
 
 use std::{
-    collections::HashMap,
     sync::Arc,
     time::{Duration, SystemTime},
 };
@@ -125,7 +124,7 @@ pub fn launch_disk_usage_global_eviction_task(
 async fn disk_usage_eviction_task(
     state: &State,
     task_config: &DiskUsageEvictionTaskConfig,
-    _storage: &GenericRemoteStorage,
+    storage: &GenericRemoteStorage,
     tenants_dir: &Utf8Path,
     cancel: CancellationToken,
 ) {
@@ -149,8 +148,14 @@ async fn disk_usage_eviction_task(
         let start = Instant::now();
 
         async {
-            let res =
-                disk_usage_eviction_task_iteration(state, task_config, tenants_dir, &cancel).await;
+            let res = disk_usage_eviction_task_iteration(
+                state,
+                task_config,
+                storage,
+                tenants_dir,
+                &cancel,
+            )
+            .await;
 
             match res {
                 Ok(()) => {}
@@ -181,12 +186,13 @@ pub trait Usage: Clone + Copy + std::fmt::Debug {
 async fn disk_usage_eviction_task_iteration(
     state: &State,
     task_config: &DiskUsageEvictionTaskConfig,
+    storage: &GenericRemoteStorage,
     tenants_dir: &Utf8Path,
     cancel: &CancellationToken,
 ) -> anyhow::Result<()> {
     let usage_pre = filesystem_level_usage::get(tenants_dir, task_config)
         .context("get filesystem-level disk usage before evictions")?;
-    let res = disk_usage_eviction_task_iteration_impl(state, usage_pre, cancel).await;
+    let res = disk_usage_eviction_task_iteration_impl(state, storage, usage_pre, cancel).await;
     match res {
         Ok(outcome) => {
             debug!(?outcome, "disk_usage_eviction_iteration finished");
@@ -268,8 +274,9 @@ struct LayerCount {
     count: usize,
 }
 
-pub async fn disk_usage_eviction_task_iteration_impl<U: Usage>(
+pub(crate) async fn disk_usage_eviction_task_iteration_impl<U: Usage>(
     state: &State,
+    _storage: &GenericRemoteStorage,
     usage_pre: U,
     cancel: &CancellationToken,
 ) -> anyhow::Result<IterationOutcome<U>> {
@@ -321,16 +328,16 @@ pub async fn disk_usage_eviction_task_iteration_impl<U: Usage>(
     // Walk through the list of candidates, until we have accumulated enough layers to get
     // us back under the pressure threshold. 'usage_planned' is updated so that it tracks
     // how much disk space would be used after evicting all the layers up to the current
-    // point in the list. The layers are collected in 'batched', grouped per timeline.
+    // point in the list.
     //
     // If we get far enough in the list that we start to evict layers that are below
     // the tenant's min-resident-size threshold, print a warning, and memorize the disk
     // usage at that point, in 'usage_planned_min_resident_size_respecting'.
-    let mut batched: HashMap<_, Vec<_>> = HashMap::new();
     let mut warned = None;
     let mut usage_planned = usage_pre;
-    let mut max_batch_size = 0;
-    for (i, (partition, candidate)) in candidates.into_iter().enumerate() {
+    let mut evicted_amount = 0;
+
+    for (i, (partition, candidate)) in candidates.iter().enumerate() {
         if !usage_planned.has_pressure() {
             debug!(
                 no_candidates_evicted = i,
@@ -339,25 +346,13 @@ pub async fn disk_usage_eviction_task_iteration_impl<U: Usage>(
             break;
         }
 
-        if partition == MinResidentSizePartition::Below && warned.is_none() {
+        if partition == &MinResidentSizePartition::Below && warned.is_none() {
             warn!(?usage_pre, ?usage_planned, candidate_no=i, "tenant_min_resident_size-respecting LRU would not relieve pressure, evicting more following global LRU policy");
             warned = Some(usage_planned);
         }
 
         usage_planned.add_available_bytes(candidate.layer.layer_desc().file_size);
-
-        // FIXME: batching makes no sense anymore because of no layermap locking, should just spawn
-        // tasks to evict all seen layers until we have evicted enough
-
-        let batch = batched.entry(TimelineKey(candidate.timeline)).or_default();
-
-        // semaphore will later be used to limit eviction concurrency, and we can express at
-        // most u32 number of permits. unlikely we would have u32::MAX layers to be evicted,
-        // but fail gracefully by not making batches larger.
-        if batch.len() < u32::MAX as usize {
-            batch.push(candidate.layer);
-            max_batch_size = max_batch_size.max(batch.len());
-        }
+        evicted_amount += 1;
     }
 
     let usage_planned = match warned {
@@ -372,100 +367,79 @@ pub async fn disk_usage_eviction_task_iteration_impl<U: Usage>(
     };
     debug!(?usage_planned, "usage planned");
 
-    // phase2: evict victims batched by timeline
+    // phase2: evict layers
 
     let mut js = tokio::task::JoinSet::new();
+    let limit = 1000;
 
-    // ratelimit to 1k files or any higher max batch size
-    let limit = Arc::new(tokio::sync::Semaphore::new(1000.max(max_batch_size)));
+    let mut evicted = candidates.into_iter().take(evicted_amount).fuse();
+    let mut consumed_all = false;
 
-    for (timeline, batch) in batched {
-        let tenant_shard_id = timeline.tenant_shard_id;
-        let timeline_id = timeline.timeline_id;
-        let batch_size =
-            u32::try_from(batch.len()).expect("batch size limited to u32::MAX during partitioning");
+    // After the evictions, `usage_assumed` is the post-eviction usage,
+    // according to internal accounting.
+    let mut usage_assumed = usage_pre;
+    let mut evictions_failed = LayerCount::default();
 
-        // I dislike naming of `available_permits` but it means current total amount of permits
-        // because permits can be added
-        assert!(batch_size as usize <= limit.available_permits());
+    let evict_layers = async move {
+        loop {
+            let next = if js.len() >= limit || consumed_all {
+                js.join_next().await
+            } else if !js.is_empty() {
+                // opportunistically consume ready result, one per each new evicted
+                futures::future::FutureExt::now_or_never(js.join_next()).and_then(|x| x)
+            } else {
+                None
+            };
 
-        debug!(%timeline_id, "evicting batch for timeline");
-
-        let evict = {
-            let limit = limit.clone();
-            let cancel = cancel.clone();
-            async move {
-                let mut evicted_bytes = 0;
-                let mut evictions_failed = LayerCount::default();
-
-                let Ok(_permit) = limit.acquire_many_owned(batch_size).await else {
-                    // semaphore closing means cancelled
-                    return (evicted_bytes, evictions_failed);
-                };
-
-                let results = timeline.evict_layers(&batch).await;
-
-                match results {
-                    Ok(results) => {
-                        assert_eq!(results.len(), batch.len());
-                        for (result, layer) in results.into_iter().zip(batch.iter()) {
-                            let file_size = layer.layer_desc().file_size;
-                            match result {
-                                Some(Ok(())) => {
-                                    evicted_bytes += file_size;
-                                }
-                                Some(Err(EvictionError::NotFound | EvictionError::Downloaded)) => {
-                                    evictions_failed.file_sizes += file_size;
-                                    evictions_failed.count += 1;
-                                }
-                                None => {
-                                    assert!(cancel.is_cancelled());
-                                }
-                            }
-                        }
+            if let Some(next) = next {
+                match next {
+                    Ok(Ok(file_size)) => {
+                        usage_assumed.add_available_bytes(file_size);
                     }
-                    Err(e) => {
-                        warn!("failed to evict batch: {:#}", e);
+                    Ok(Err((file_size, EvictionError::NotFound | EvictionError::Downloaded))) => {
+                        evictions_failed.file_sizes += file_size;
+                        evictions_failed.count += 1;
                     }
+                    Err(je) if je.is_cancelled() => unreachable!("not used"),
+                    Err(je) if je.is_panic() => { /* already logged */ }
+                    Err(je) => tracing::error!("unknown JoinError: {je:?}"),
                 }
-                (evicted_bytes, evictions_failed)
             }
-        }
-        .instrument(tracing::info_span!("evict_batch", tenant_id=%tenant_shard_id.tenant_id, shard_id=%tenant_shard_id.shard_slug(), %timeline_id, batch_size));
 
-        js.spawn(evict);
-
-        // spwaning multiple thousands of these is essentially blocking, so give already spawned a
-        // chance of making progress
-        tokio::task::yield_now().await;
-    }
-
-    let join_all = async move {
-        // After the evictions, `usage_assumed` is the post-eviction usage,
-        // according to internal accounting.
-        let mut usage_assumed = usage_pre;
-        let mut evictions_failed = LayerCount::default();
-
-        while let Some(res) = js.join_next().await {
-            match res {
-                Ok((evicted_bytes, failed)) => {
-                    usage_assumed.add_available_bytes(evicted_bytes);
-                    evictions_failed.file_sizes += failed.file_sizes;
-                    evictions_failed.count += failed.count;
-                }
-                Err(je) if je.is_cancelled() => unreachable!("not used"),
-                Err(je) if je.is_panic() => { /* already logged */ }
-                Err(je) => tracing::error!("unknown JoinError: {je:?}"),
+            if consumed_all && js.is_empty() {
+                break;
             }
+
+            // calling again when consumed_all is fine as evicted is fused.
+            let Some((_partition, candidate)) = evicted.next() else {
+                consumed_all = true;
+                continue;
+            };
+
+            js.spawn(async move {
+                let rtc = candidate.timeline.remote_client.as_ref().expect(
+                    "holding the witness, all timelines must have a remote timeline client",
+                );
+                let file_size = candidate.layer.layer_desc().file_size;
+                candidate
+                    .layer
+                    .evict_and_wait(rtc)
+                    .await
+                    .map(|()| file_size)
+                    .map_err(|e| (file_size, e))
+            });
+
+            tokio::task::yield_now().await;
         }
+
         (usage_assumed, evictions_failed)
     };
 
     let (usage_assumed, evictions_failed) = tokio::select! {
-        tuple = join_all => { tuple },
+        tuple = evict_layers => { tuple },
         _ = cancel.cancelled() => {
-            // close the semaphore to stop any pending acquires
-            limit.close();
+            // dropping joinset will abort all pending evict_and_waits and that is fine, our
+            // requests will still stand
             return Ok(IterationOutcome::Cancelled);
         }
     };

pageserver/src/http/openapi_spec.yml

@@ -992,8 +992,8 @@ paths:
           type: string
     post:
       description: |
-        Create a timeline. Returns new timeline id on success.\
-        If no new timeline id is specified in parameters, it would be generated. It's an error to recreate the same timeline.
+        Create a timeline. Returns new timeline id on success.
+        Recreating the same timeline will succeed if the parameters match the existing timeline.
         If no pg_version is specified, assume DEFAULT_PG_VERSION hardcoded in the pageserver.
       requestBody:
         content:
@@ -1405,6 +1405,8 @@ components:
           type: integer
         trace_read_requests:
           type: boolean
+        heatmap_period:
+          type: integer
     TenantConfigResponse:
       type: object
       properties:

pageserver/src/http/routes.rs

@@ -38,6 +38,7 @@ use crate::tenant::mgr::{
     GetTenantError, SetNewTenantConfigError, TenantManager, TenantMapError, TenantMapInsertError,
     TenantSlotError, TenantSlotUpsertError, TenantStateError,
 };
+use crate::tenant::secondary::SecondaryController;
 use crate::tenant::size::ModelInputs;
 use crate::tenant::storage_layer::LayerAccessStatsReset;
 use crate::tenant::timeline::CompactFlags;
@@ -75,9 +76,11 @@ pub struct State {
     broker_client: storage_broker::BrokerClientChannel,
     disk_usage_eviction_state: Arc<disk_usage_eviction_task::State>,
     deletion_queue_client: DeletionQueueClient,
+    secondary_controller: SecondaryController,
 }
 
 impl State {
+    #[allow(clippy::too_many_arguments)]
     pub fn new(
         conf: &'static PageServerConf,
         tenant_manager: Arc<TenantManager>,
@@ -86,6 +89,7 @@ impl State {
         broker_client: storage_broker::BrokerClientChannel,
         disk_usage_eviction_state: Arc<disk_usage_eviction_task::State>,
         deletion_queue_client: DeletionQueueClient,
+        secondary_controller: SecondaryController,
     ) -> anyhow::Result<Self> {
         let allowlist_routes = ["/v1/status", "/v1/doc", "/swagger.yml", "/metrics"]
             .iter()
@@ -100,6 +104,7 @@ impl State {
             broker_client,
             disk_usage_eviction_state,
             deletion_queue_client,
+            secondary_controller,
         })
     }
 
@@ -136,11 +141,6 @@ impl From<PageReconstructError> for ApiError {
     fn from(pre: PageReconstructError) -> ApiError {
         match pre {
             PageReconstructError::Other(pre) => ApiError::InternalServerError(pre),
-            PageReconstructError::NeedsDownload(_, _) => {
-                // This shouldn't happen, because we use a RequestContext that requests to
-                // download any missing layer files on-demand.
-                ApiError::InternalServerError(anyhow::anyhow!("need to download remote layer file"))
-            }
             PageReconstructError::Cancelled => {
                 ApiError::InternalServerError(anyhow::anyhow!("request was cancelled"))
             }
@@ -453,7 +453,7 @@ async fn timeline_create_handler(
                     .map_err(ApiError::InternalServerError)?;
                 json_response(StatusCode::CREATED, timeline_info)
             }
-            Err(tenant::CreateTimelineError::AlreadyExists) => {
+            Err(tenant::CreateTimelineError::Conflict | tenant::CreateTimelineError::AlreadyCreating) => {
                 json_response(StatusCode::CONFLICT, ())
             }
             Err(tenant::CreateTimelineError::AncestorLsn(err)) => {
@@ -1546,7 +1546,7 @@ async fn always_panic_handler(
 
 async fn disk_usage_eviction_run(
     mut r: Request<Body>,
-    _cancel: CancellationToken,
+    cancel: CancellationToken,
 ) -> Result<Response<Body>, ApiError> {
     check_permission(&r, None)?;
 
@@ -1583,48 +1583,41 @@ async fn disk_usage_eviction_run(
         freed_bytes: 0,
     };
 
-    let (tx, rx) = tokio::sync::oneshot::channel();
-
     let state = get_state(&r);
 
-    if state.remote_storage.as_ref().is_none() {
+    let Some(storage) = state.remote_storage.as_ref() else {
         return Err(ApiError::InternalServerError(anyhow::anyhow!(
             "remote storage not configured, cannot run eviction iteration"
         )));
-    }
+    };
 
     let state = state.disk_usage_eviction_state.clone();
 
-    let cancel = CancellationToken::new();
-    let child_cancel = cancel.clone();
-    let _g = cancel.drop_guard();
+    let res = crate::disk_usage_eviction_task::disk_usage_eviction_task_iteration_impl(
+        &state, storage, usage, &cancel,
+    )
+    .await;
 
-    crate::task_mgr::spawn(
-        crate::task_mgr::BACKGROUND_RUNTIME.handle(),
-        TaskKind::DiskUsageEviction,
-        None,
-        None,
-        "ondemand disk usage eviction",
-        false,
-        async move {
-            let res = crate::disk_usage_eviction_task::disk_usage_eviction_task_iteration_impl(
-                &state,
-                usage,
-                &child_cancel,
-            )
-            .await;
+    info!(?res, "disk_usage_eviction_task_iteration_impl finished");
 
-            info!(?res, "disk_usage_eviction_task_iteration_impl finished");
+    let res = res.map_err(ApiError::InternalServerError)?;
 
-            let _ = tx.send(res);
-            Ok(())
-        }
-        .in_current_span(),
-    );
+    json_response(StatusCode::OK, res)
+}
 
-    let response = rx.await.unwrap().map_err(ApiError::InternalServerError)?;
+async fn secondary_upload_handler(
+    request: Request<Body>,
+    _cancel: CancellationToken,
+) -> Result<Response<Body>, ApiError> {
+    let state = get_state(&request);
+    let tenant_shard_id: TenantShardId = parse_request_param(&request, "tenant_shard_id")?;
+    state
+        .secondary_controller
+        .upload_tenant(tenant_shard_id)
+        .await
+        .map_err(ApiError::InternalServerError)?;
 
-    json_response(StatusCode::OK, response)
+    json_response(StatusCode::OK, ())
 }
 
 async fn handler_404(_: Request<Body>) -> Result<Response<Body>, ApiError> {
@@ -1886,6 +1879,9 @@ pub fn make_router(
             "/v1/tenant/:tenant_shard_id/timeline/:timeline_id/layer/:layer_file_name",
             |r| api_handler(r, evict_timeline_layer_handler),
         )
+        .post("/v1/tenant/:tenant_shard_id/heatmap_upload", |r| {
+            api_handler(r, secondary_upload_handler)
+        })
         .put("/v1/disk_usage_eviction/run", |r| {
             api_handler(r, disk_usage_eviction_run)
         })

pageserver/src/metrics.rs

@@ -2,9 +2,10 @@ use enum_map::EnumMap;
 use metrics::metric_vec_duration::DurationResultObserver;
 use metrics::{
     register_counter_vec, register_gauge_vec, register_histogram, register_histogram_vec,
-    register_int_counter, register_int_counter_vec, register_int_gauge, register_int_gauge_vec,
-    register_uint_gauge, register_uint_gauge_vec, Counter, CounterVec, GaugeVec, Histogram,
-    HistogramVec, IntCounter, IntCounterVec, IntGauge, IntGaugeVec, UIntGauge, UIntGaugeVec,
+    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,
+    Counter, CounterVec, GaugeVec, Histogram, HistogramVec, IntCounter, IntCounterPairVec,
+    IntCounterVec, IntGauge, IntGaugeVec, UIntGauge, UIntGaugeVec,
 };
 use once_cell::sync::Lazy;
 use pageserver_api::shard::TenantShardId;
@@ -1270,6 +1271,28 @@ pub(crate) static WAL_INGEST: Lazy<WalIngestMetrics> = Lazy::new(|| WalIngestMet
     )
     .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) 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 S3 client"
+    )
+    .expect("failed to define a metric"),
+});
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum RemoteOpKind {
@@ -1321,25 +1344,16 @@ pub(crate) static TENANT_TASK_EVENTS: Lazy<IntCounterVec> = Lazy::new(|| {
     .expect("Failed to register tenant_task_events metric")
 });
 
-pub(crate) static BACKGROUND_LOOP_SEMAPHORE_WAIT_START_COUNT: Lazy<IntCounterVec> =
-    Lazy::new(|| {
-        register_int_counter_vec!(
-            "pageserver_background_loop_semaphore_wait_start_count",
-            "Counter for background loop concurrency-limiting semaphore acquire calls started",
-            &["task"],
-        )
-        .unwrap()
-    });
-
-pub(crate) static BACKGROUND_LOOP_SEMAPHORE_WAIT_FINISH_COUNT: Lazy<IntCounterVec> =
-    Lazy::new(|| {
-        register_int_counter_vec!(
-            "pageserver_background_loop_semaphore_wait_finish_count",
-            "Counter for background loop concurrency-limiting semaphore acquire calls finished",
-            &["task"],
-        )
-        .unwrap()
-    });
+pub(crate) static BACKGROUND_LOOP_SEMAPHORE_WAIT_GAUGE: Lazy<IntCounterPairVec> = Lazy::new(|| {
+    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()
+});
 
 pub(crate) static BACKGROUND_LOOP_PERIOD_OVERRUN_COUNT: Lazy<IntCounterVec> = Lazy::new(|| {
     register_int_counter_vec!(

pageserver/src/task_mgr.rs

@@ -258,6 +258,9 @@ pub enum TaskKind {
     /// See [`crate::disk_usage_eviction_task`].
     DiskUsageEviction,
 
+    /// See [`crate::tenant::secondary`].
+    SecondaryUploads,
+
     // Initial logical size calculation
     InitialLogicalSizeCalculation,
 

pageserver/src/tenant.rs

@@ -48,6 +48,7 @@ use self::mgr::GetActiveTenantError;
 use self::mgr::GetTenantError;
 use self::mgr::TenantsMap;
 use self::remote_timeline_client::RemoteTimelineClient;
+use self::timeline::uninit::TimelineExclusionError;
 use self::timeline::uninit::TimelineUninitMark;
 use self::timeline::uninit::UninitializedTimeline;
 use self::timeline::EvictionTaskTenantState;
@@ -87,7 +88,6 @@ use std::process::Stdio;
 use std::sync::atomic::AtomicU64;
 use std::sync::atomic::Ordering;
 use std::sync::Arc;
-use std::sync::MutexGuard;
 use std::sync::{Mutex, RwLock};
 use std::time::{Duration, Instant};
 
@@ -144,6 +144,7 @@ pub mod storage_layer;
 pub mod config;
 pub mod delete;
 pub mod mgr;
+pub mod secondary;
 pub mod tasks;
 pub mod upload_queue;
 
@@ -248,6 +249,12 @@ pub struct Tenant {
     generation: Generation,
 
     timelines: Mutex<HashMap<TimelineId, Arc<Timeline>>>,
+
+    /// During timeline creation, we first insert the TimelineId to the
+    /// creating map, then `timelines`, then remove it from the creating map.
+    /// **Lock order**: if acquring both, acquire`timelines` before `timelines_creating`
+    timelines_creating: std::sync::Mutex<HashSet<TimelineId>>,
+
     // This mutex prevents creation of new timelines during GC.
     // Adding yet another mutex (in addition to `timelines`) is needed because holding
     // `timelines` mutex during all GC iteration
@@ -406,8 +413,10 @@ impl Debug for SetStoppingError {
 
 #[derive(thiserror::Error, Debug)]
 pub enum CreateTimelineError {
-    #[error("a timeline with the given ID already exists")]
-    AlreadyExists,
+    #[error("creation of timeline with the given ID is in progress")]
+    AlreadyCreating,
+    #[error("timeline already exists with different parameters")]
+    Conflict,
     #[error(transparent)]
     AncestorLsn(anyhow::Error),
     #[error("ancestor timeline is not active")]
@@ -1457,7 +1466,7 @@ impl Tenant {
     /// For tests, use `DatadirModification::init_empty_test_timeline` + `commit` to setup the
     /// minimum amount of keys required to get a writable timeline.
     /// (Without it, `put` might fail due to `repartition` failing.)
-    pub async fn create_empty_timeline(
+    pub(crate) async fn create_empty_timeline(
         &self,
         new_timeline_id: TimelineId,
         initdb_lsn: Lsn,
@@ -1469,10 +1478,7 @@ impl Tenant {
             "Cannot create empty timelines on inactive tenant"
         );
 
-        let timeline_uninit_mark = {
-            let timelines = self.timelines.lock().unwrap();
-            self.create_timeline_uninit_mark(new_timeline_id, &timelines)?
-        };
+        let timeline_uninit_mark = self.create_timeline_uninit_mark(new_timeline_id)?;
         let new_metadata = TimelineMetadata::new(
             // Initialize disk_consistent LSN to 0, The caller must import some data to
             // make it valid, before calling finish_creation()
@@ -1549,7 +1555,7 @@ impl Tenant {
     /// If the caller specified the timeline ID to use (`new_timeline_id`), and timeline with
     /// the same timeline ID already exists, returns CreateTimelineError::AlreadyExists.
     #[allow(clippy::too_many_arguments)]
-    pub async fn create_timeline(
+    pub(crate) async fn create_timeline(
         &self,
         new_timeline_id: TimelineId,
         ancestor_timeline_id: Option<TimelineId>,
@@ -1570,26 +1576,51 @@ impl Tenant {
             .enter()
             .map_err(|_| CreateTimelineError::ShuttingDown)?;
 
-        if let Ok(existing) = self.get_timeline(new_timeline_id, false) {
-            debug!("timeline {new_timeline_id} already exists");
-
-            if let Some(remote_client) = existing.remote_client.as_ref() {
-                // Wait for uploads to complete, so that when we return Ok, the timeline
-                // is known to be durable on remote storage. Just like we do at the end of
-                // this function, after we have created the timeline ourselves.
-                //
-                // We only really care that the initial version of `index_part.json` has
-                // been uploaded. That's enough to remember that the timeline
-                // exists. However, there is no function to wait specifically for that so
-                // we just wait for all in-progress uploads to finish.
-                remote_client
-                    .wait_completion()
-                    .await
-                    .context("wait for timeline uploads to complete")?;
+        // Get exclusive access to the timeline ID: this ensures that it does not already exist,
+        // and that no other creation attempts will be allowed in while we are working.  The
+        // uninit_mark is a guard.
+        let uninit_mark = match self.create_timeline_uninit_mark(new_timeline_id) {
+            Ok(m) => m,
+            Err(TimelineExclusionError::AlreadyCreating) => {
+                // Creation is in progress, we cannot create it again, and we cannot
+                // check if this request matches the existing one, so caller must try
+                // again later.
+                return Err(CreateTimelineError::AlreadyCreating);
             }
+            Err(TimelineExclusionError::Other(e)) => {
+                return Err(CreateTimelineError::Other(e));
+            }
+            Err(TimelineExclusionError::AlreadyExists(existing)) => {
+                debug!("timeline {new_timeline_id} already exists");
 
-            return Err(CreateTimelineError::AlreadyExists);
-        }
+                // Idempotency: creating the same timeline twice is not an error, unless
+                // the second creation has different parameters.
+                if existing.get_ancestor_timeline_id() != ancestor_timeline_id
+                    || existing.pg_version != pg_version
+                    || (ancestor_start_lsn.is_some()
+                        && ancestor_start_lsn != Some(existing.get_ancestor_lsn()))
+                {
+                    return Err(CreateTimelineError::Conflict);
+                }
+
+                if let Some(remote_client) = existing.remote_client.as_ref() {
+                    // Wait for uploads to complete, so that when we return Ok, the timeline
+                    // is known to be durable on remote storage. Just like we do at the end of
+                    // this function, after we have created the timeline ourselves.
+                    //
+                    // We only really care that the initial version of `index_part.json` has
+                    // been uploaded. That's enough to remember that the timeline
+                    // exists. However, there is no function to wait specifically for that so
+                    // we just wait for all in-progress uploads to finish.
+                    remote_client
+                        .wait_completion()
+                        .await
+                        .context("wait for timeline uploads to complete")?;
+                }
+
+                return Ok(existing);
+            }
+        };
 
         let loaded_timeline = match ancestor_timeline_id {
             Some(ancestor_timeline_id) => {
@@ -1626,18 +1657,32 @@ impl Tenant {
                     ancestor_timeline.wait_lsn(*lsn, ctx).await?;
                 }
 
-                self.branch_timeline(&ancestor_timeline, new_timeline_id, ancestor_start_lsn, ctx)
-                    .await?
+                self.branch_timeline(
+                    &ancestor_timeline,
+                    new_timeline_id,
+                    ancestor_start_lsn,
+                    uninit_mark,
+                    ctx,
+                )
+                .await?
             }
             None => {
-                self.bootstrap_timeline(new_timeline_id, pg_version, load_existing_initdb, ctx)
-                    .await?
+                self.bootstrap_timeline(
+                    new_timeline_id,
+                    pg_version,
+                    load_existing_initdb,
+                    uninit_mark,
+                    ctx,
+                )
+                .await?
             }
         };
 
+        // At this point we have dropped our guard on [`Self::timelines_creating`], and
+        // the timeline is visible in [`Self::timelines`], but it is _not_ durable yet.  We must
+        // not send a success to the caller until it is.  The same applies to handling retries,
+        // see the handling of [`TimelineExclusionError::AlreadyExists`] above.
         if let Some(remote_client) = loaded_timeline.remote_client.as_ref() {
-            // Wait for the upload of the 'index_part.json` file to finish, so that when we return
-            // Ok, the timeline is durable in remote storage.
             let kind = ancestor_timeline_id
                 .map(|_| "branched")
                 .unwrap_or("bootstrapped");
@@ -2114,6 +2159,14 @@ impl Tenant {
             .attach_mode
             .clone()
     }
+
+    pub(crate) fn get_tenant_shard_id(&self) -> &TenantShardId {
+        &self.tenant_shard_id
+    }
+
+    pub(crate) fn get_generation(&self) -> Generation {
+        self.generation
+    }
 }
 
 /// Given a Vec of timelines and their ancestors (timeline_id, ancestor_id),
@@ -2252,6 +2305,18 @@ impl Tenant {
             .or(self.conf.default_tenant_conf.min_resident_size_override)
     }
 
+    pub fn get_heatmap_period(&self) -> Option<Duration> {
+        let tenant_conf = self.tenant_conf.read().unwrap().tenant_conf;
+        let heatmap_period = tenant_conf
+            .heatmap_period
+            .unwrap_or(self.conf.default_tenant_conf.heatmap_period);
+        if heatmap_period.is_zero() {
+            None
+        } else {
+            Some(heatmap_period)
+        }
+    }
+
     pub fn set_new_tenant_config(&self, new_tenant_conf: TenantConfOpt) {
         self.tenant_conf.write().unwrap().tenant_conf = new_tenant_conf;
         // Don't hold self.timelines.lock() during the notifies.
@@ -2401,6 +2466,7 @@ impl Tenant {
             loading_started_at: Instant::now(),
             tenant_conf: Arc::new(RwLock::new(attached_conf)),
             timelines: Mutex::new(HashMap::new()),
+            timelines_creating: Mutex::new(HashSet::new()),
             gc_cs: tokio::sync::Mutex::new(()),
             walredo_mgr,
             remote_storage,
@@ -2792,8 +2858,9 @@ impl Tenant {
         start_lsn: Option<Lsn>,
         ctx: &RequestContext,
     ) -> Result<Arc<Timeline>, CreateTimelineError> {
+        let uninit_mark = self.create_timeline_uninit_mark(dst_id).unwrap();
         let tl = self
-            .branch_timeline_impl(src_timeline, dst_id, start_lsn, ctx)
+            .branch_timeline_impl(src_timeline, dst_id, start_lsn, uninit_mark, ctx)
             .await?;
         tl.set_state(TimelineState::Active);
         Ok(tl)
@@ -2807,9 +2874,10 @@ impl Tenant {
         src_timeline: &Arc<Timeline>,
         dst_id: TimelineId,
         start_lsn: Option<Lsn>,
+        timeline_uninit_mark: TimelineUninitMark<'_>,
         ctx: &RequestContext,
     ) -> Result<Arc<Timeline>, CreateTimelineError> {
-        self.branch_timeline_impl(src_timeline, dst_id, start_lsn, ctx)
+        self.branch_timeline_impl(src_timeline, dst_id, start_lsn, timeline_uninit_mark, ctx)
             .await
     }
 
@@ -2818,13 +2886,14 @@ impl Tenant {
         src_timeline: &Arc<Timeline>,
         dst_id: TimelineId,
         start_lsn: Option<Lsn>,
+        timeline_uninit_mark: TimelineUninitMark<'_>,
         _ctx: &RequestContext,
     ) -> Result<Arc<Timeline>, CreateTimelineError> {
         let src_id = src_timeline.timeline_id;
 
-        // First acquire the GC lock so that another task cannot advance the GC
-        // cutoff in 'gc_info', and make 'start_lsn' invalid, while we are
-        // creating the branch.
+        // We will validate our ancestor LSN in this function.  Acquire the GC lock so that
+        // this check cannot race with GC, and the ancestor LSN is guaranteed to remain
+        // valid while we are creating the branch.
         let _gc_cs = self.gc_cs.lock().await;
 
         // If no start LSN is specified, we branch the new timeline from the source timeline's last record LSN
@@ -2834,13 +2903,6 @@ impl Tenant {
             lsn
         });
 
-        // Create a placeholder for the new branch. This will error
-        // out if the new timeline ID is already in use.
-        let timeline_uninit_mark = {
-            let timelines = self.timelines.lock().unwrap();
-            self.create_timeline_uninit_mark(dst_id, &timelines)?
-        };
-
         // Ensure that `start_lsn` is valid, i.e. the LSN is within the PITR
         // horizon on the source timeline
         //
@@ -2932,21 +2994,38 @@ impl Tenant {
         Ok(new_timeline)
     }
 
-    /// - run initdb to init temporary instance and get bootstrap data
-    /// - after initialization completes, tar up the temp dir and upload it to S3.
-    ///
-    /// The caller is responsible for activating the returned timeline.
-    pub(crate) async fn bootstrap_timeline(
+    /// For unit tests, make this visible so that other modules can directly create timelines
+    #[cfg(test)]
+    pub(crate) async fn bootstrap_timeline_test(
         &self,
         timeline_id: TimelineId,
         pg_version: u32,
         load_existing_initdb: Option<TimelineId>,
         ctx: &RequestContext,
     ) -> anyhow::Result<Arc<Timeline>> {
-        let timeline_uninit_mark = {
-            let timelines = self.timelines.lock().unwrap();
-            self.create_timeline_uninit_mark(timeline_id, &timelines)?
-        };
+        let uninit_mark = self.create_timeline_uninit_mark(timeline_id).unwrap();
+        self.bootstrap_timeline(
+            timeline_id,
+            pg_version,
+            load_existing_initdb,
+            uninit_mark,
+            ctx,
+        )
+        .await
+    }
+
+    /// - run initdb to init temporary instance and get bootstrap data
+    /// - after initialization completes, tar up the temp dir and upload it to S3.
+    ///
+    /// The caller is responsible for activating the returned timeline.
+    async fn bootstrap_timeline(
+        &self,
+        timeline_id: TimelineId,
+        pg_version: u32,
+        load_existing_initdb: Option<TimelineId>,
+        timeline_uninit_mark: TimelineUninitMark<'_>,
+        ctx: &RequestContext,
+    ) -> anyhow::Result<Arc<Timeline>> {
         // create a `tenant/{tenant_id}/timelines/basebackup-{timeline_id}.{TEMP_FILE_SUFFIX}/`
         // temporary directory for basebackup files for the given timeline.
 
@@ -3143,11 +3222,11 @@ impl Tenant {
     /// at 'disk_consistent_lsn'. After any initial data has been imported, call
     /// `finish_creation` to insert the Timeline into the timelines map and to remove the
     /// uninit mark file.
-    async fn prepare_new_timeline(
-        &self,
+    async fn prepare_new_timeline<'a>(
+        &'a self,
         new_timeline_id: TimelineId,
         new_metadata: &TimelineMetadata,
-        uninit_mark: TimelineUninitMark,
+        uninit_mark: TimelineUninitMark<'a>,
         start_lsn: Lsn,
         ancestor: Option<Arc<Timeline>>,
     ) -> anyhow::Result<UninitializedTimeline> {
@@ -3220,23 +3299,38 @@ impl Tenant {
     fn create_timeline_uninit_mark(
         &self,
         timeline_id: TimelineId,
-        timelines: &MutexGuard<HashMap<TimelineId, Arc<Timeline>>>,
-    ) -> anyhow::Result<TimelineUninitMark> {
+    ) -> Result<TimelineUninitMark, TimelineExclusionError> {
         let tenant_shard_id = self.tenant_shard_id;
 
-        anyhow::ensure!(
-            timelines.get(&timeline_id).is_none(),
-            "Timeline {tenant_shard_id}/{timeline_id} already exists in pageserver's memory"
-        );
-        let timeline_path = self.conf.timeline_path(&tenant_shard_id, &timeline_id);
-        anyhow::ensure!(
-            !timeline_path.exists(),
-            "Timeline {timeline_path} already exists, cannot create its uninit mark file",
-        );
-
         let uninit_mark_path = self
             .conf
             .timeline_uninit_mark_file_path(tenant_shard_id, timeline_id);
+        let timeline_path = self.conf.timeline_path(&tenant_shard_id, &timeline_id);
+
+        let uninit_mark = TimelineUninitMark::new(
+            self,
+            timeline_id,
+            uninit_mark_path.clone(),
+            timeline_path.clone(),
+        )?;
+
+        // At this stage, we have got exclusive access to in-memory state for this timeline ID
+        // for creation.
+        // A timeline directory should never exist on disk already:
+        // - a previous failed creation would have cleaned up after itself
+        // - a pageserver restart would clean up timeline directories that don't have valid remote state
+        //
+        // Therefore it is an unexpected internal error to encounter a timeline directory already existing here,
+        // this error may indicate a bug in cleanup on failed creations.
+        if timeline_path.exists() {
+            return Err(TimelineExclusionError::Other(anyhow::anyhow!(
+                "Timeline directory already exists! This is a bug."
+            )));
+        }
+
+        // Create the on-disk uninit mark _after_ the in-memory acquisition of the tenant ID: guarantees
+        // that during process runtime, colliding creations will be caught in-memory without getting
+        // as far as failing to write a file.
         fs::OpenOptions::new()
             .write(true)
             .create_new(true)
@@ -3250,8 +3344,6 @@ impl Tenant {
                 format!("Failed to crate uninit mark for timeline {tenant_shard_id}/{timeline_id}")
             })?;
 
-        let uninit_mark = TimelineUninitMark::new(uninit_mark_path, timeline_path);
-
         Ok(uninit_mark)
     }
 
@@ -3694,6 +3786,7 @@ pub(crate) mod harness {
                     tenant_conf.evictions_low_residence_duration_metric_threshold,
                 ),
                 gc_feedback: Some(tenant_conf.gc_feedback),
+                heatmap_period: Some(tenant_conf.heatmap_period),
             }
         }
     }
@@ -4000,13 +4093,7 @@ mod tests {
             .await
         {
             Ok(_) => panic!("duplicate timeline creation should fail"),
-            Err(e) => assert_eq!(
-                e.to_string(),
-                format!(
-                    "Timeline {}/{} already exists in pageserver's memory",
-                    tenant.tenant_shard_id, TIMELINE_ID
-                )
-            ),
+            Err(e) => assert_eq!(e.to_string(), "Already exists".to_string()),
         }
 
         Ok(())

pageserver/src/tenant/config.rs

@@ -334,6 +334,11 @@ pub struct TenantConf {
     #[serde(with = "humantime_serde")]
     pub evictions_low_residence_duration_metric_threshold: Duration,
     pub gc_feedback: bool,
+
+    /// If non-zero, the period between uploads of a heatmap from attached tenants.  This
+    /// may be disabled if a Tenant will not have secondary locations: only secondary
+    /// locations will use the heatmap uploaded by attached locations.
+    pub heatmap_period: Duration,
 }
 
 /// Same as TenantConf, but this struct preserves the information about
@@ -414,6 +419,11 @@ pub struct TenantConfOpt {
     #[serde(skip_serializing_if = "Option::is_none")]
     #[serde(default)]
     pub gc_feedback: Option<bool>,
+
+    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(with = "humantime_serde")]
+    #[serde(default)]
+    pub heatmap_period: Option<Duration>,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
@@ -482,6 +492,7 @@ impl TenantConfOpt {
                 .evictions_low_residence_duration_metric_threshold
                 .unwrap_or(global_conf.evictions_low_residence_duration_metric_threshold),
             gc_feedback: self.gc_feedback.unwrap_or(global_conf.gc_feedback),
+            heatmap_period: self.heatmap_period.unwrap_or(global_conf.heatmap_period),
         }
     }
 }
@@ -519,6 +530,7 @@ impl Default for TenantConf {
             )
             .expect("cannot parse default evictions_low_residence_duration_metric_threshold"),
             gc_feedback: false,
+            heatmap_period: Duration::ZERO,
         }
     }
 }

pageserver/src/tenant/mgr.rs

@@ -807,6 +807,12 @@ pub(crate) async fn set_new_tenant_config(
 }
 
 impl TenantManager {
+    /// Convenience function so that anyone with a TenantManager can get at the global configuration, without
+    /// having to pass it around everywhere as a separate object.
+    pub(crate) fn get_conf(&self) -> &'static PageServerConf {
+        self.conf
+    }
+
     /// Gets the attached tenant from the in-memory data, erroring if it's absent, in secondary mode, or is not fitting to the query.
     /// `active_only = true` allows to query only tenants that are ready for operations, erroring on other kinds of tenants.
     pub(crate) fn get_attached_tenant_shard(
@@ -1087,6 +1093,20 @@ impl TenantManager {
 
         Ok(())
     }
+
+    pub(crate) fn get_attached_active_tenant_shards(&self) -> Vec<Arc<Tenant>> {
+        let locked = self.tenants.read().unwrap();
+        match &*locked {
+            TenantsMap::Initializing => Vec::new(),
+            TenantsMap::Open(map) | TenantsMap::ShuttingDown(map) => map
+                .values()
+                .filter_map(|slot| {
+                    slot.get_attached()
+                        .and_then(|t| if t.is_active() { Some(t.clone()) } else { None })
+                })
+                .collect(),
+        }
+    }
 }
 
 #[derive(Debug, thiserror::Error)]

pageserver/src/tenant/remote_timeline_client.rs

@@ -180,7 +180,7 @@
 //! [`Tenant::timeline_init_and_sync`]: super::Tenant::timeline_init_and_sync
 //! [`Timeline::load_layer_map`]: super::Timeline::load_layer_map
 
-mod download;
+pub(crate) mod download;
 pub mod index;
 mod upload;
 
@@ -1604,6 +1604,23 @@ impl RemoteTimelineClient {
             }
         }
     }
+
+    pub(crate) fn get_layers_metadata(
+        &self,
+        layers: Vec<LayerFileName>,
+    ) -> anyhow::Result<Vec<Option<LayerFileMetadata>>> {
+        let q = self.upload_queue.lock().unwrap();
+        let q = match &*q {
+            UploadQueue::Stopped(_) | UploadQueue::Uninitialized => {
+                anyhow::bail!("queue is in state {}", q.as_str())
+            }
+            UploadQueue::Initialized(inner) => inner,
+        };
+
+        let decorated = layers.into_iter().map(|l| q.latest_files.get(&l).cloned());
+
+        Ok(decorated.collect())
+    }
 }
 
 pub fn remote_timelines_path(tenant_shard_id: &TenantShardId) -> RemotePath {
@@ -1659,6 +1676,13 @@ pub fn remote_index_path(
     .expect("Failed to construct path")
 }
 
+pub const HEATMAP_BASENAME: &str = "heatmap-v1.json";
+
+pub(crate) fn remote_heatmap_path(tenant_shard_id: &TenantShardId) -> RemotePath {
+    RemotePath::from_string(&format!("tenants/{tenant_shard_id}/{HEATMAP_BASENAME}"))
+        .expect("Failed to construct path")
+}
+
 /// Given the key of an index, parse out the generation part of the name
 pub fn parse_remote_index_path(path: RemotePath) -> Option<Generation> {
     let file_name = match path.get_path().file_name() {

pageserver/src/tenant/secondary.rs

@@ -0,0 +1,104 @@
+pub mod heatmap;
+mod heatmap_uploader;
+
+use std::sync::Arc;
+
+use crate::task_mgr::{self, TaskKind, BACKGROUND_RUNTIME};
+
+use self::heatmap_uploader::heatmap_uploader_task;
+
+use super::mgr::TenantManager;
+
+use pageserver_api::shard::TenantShardId;
+use remote_storage::GenericRemoteStorage;
+
+use tokio_util::sync::CancellationToken;
+use utils::completion::Barrier;
+
+enum UploadCommand {
+    Upload(TenantShardId),
+}
+
+struct CommandRequest<T> {
+    payload: T,
+    response_tx: tokio::sync::oneshot::Sender<CommandResponse>,
+}
+
+struct CommandResponse {
+    result: anyhow::Result<()>,
+}
+
+/// The SecondaryController is a pseudo-rpc client for administrative control of secondary mode downloads,
+/// and heatmap uploads.  This is not a hot data path: it's primarily a hook for tests,
+/// where we want to immediately upload/download for a particular tenant.  In normal operation
+/// uploads & downloads are autonomous and not driven by this interface.
+pub struct SecondaryController {
+    upload_req_tx: tokio::sync::mpsc::Sender<CommandRequest<UploadCommand>>,
+}
+
+impl SecondaryController {
+    async fn dispatch<T>(
+        &self,
+        queue: &tokio::sync::mpsc::Sender<CommandRequest<T>>,
+        payload: T,
+    ) -> anyhow::Result<()> {
+        let (response_tx, response_rx) = tokio::sync::oneshot::channel();
+
+        queue
+            .send(CommandRequest {
+                payload,
+                response_tx,
+            })
+            .await
+            .map_err(|_| anyhow::anyhow!("Receiver shut down"))?;
+
+        let response = response_rx
+            .await
+            .map_err(|_| anyhow::anyhow!("Request dropped"))?;
+
+        response.result
+    }
+
+    pub async fn upload_tenant(&self, tenant_shard_id: TenantShardId) -> anyhow::Result<()> {
+        self.dispatch(&self.upload_req_tx, UploadCommand::Upload(tenant_shard_id))
+            .await
+    }
+}
+
+pub fn spawn_tasks(
+    tenant_manager: Arc<TenantManager>,
+    remote_storage: GenericRemoteStorage,
+    background_jobs_can_start: Barrier,
+    cancel: CancellationToken,
+) -> SecondaryController {
+    let (upload_req_tx, upload_req_rx) =
+        tokio::sync::mpsc::channel::<CommandRequest<UploadCommand>>(16);
+
+    task_mgr::spawn(
+        BACKGROUND_RUNTIME.handle(),
+        TaskKind::SecondaryUploads,
+        None,
+        None,
+        "heatmap uploads",
+        false,
+        async move {
+            heatmap_uploader_task(
+                tenant_manager,
+                remote_storage,
+                upload_req_rx,
+                background_jobs_can_start,
+                cancel,
+            )
+            .await
+        },
+    );
+
+    SecondaryController { upload_req_tx }
+}
+
+/// For running with remote storage disabled: a SecondaryController that is connected to nothing.
+pub fn null_controller() -> SecondaryController {
+    let (upload_req_tx, _upload_req_rx) =
+        tokio::sync::mpsc::channel::<CommandRequest<UploadCommand>>(16);
+    SecondaryController { upload_req_tx }
+}

pageserver/src/tenant/secondary/heatmap.rs

@@ -0,0 +1,64 @@
+use std::time::SystemTime;
+
+use crate::tenant::{
+    remote_timeline_client::index::IndexLayerMetadata, storage_layer::LayerFileName,
+};
+
+use serde::{Deserialize, Serialize};
+use serde_with::{serde_as, DisplayFromStr, TimestampSeconds};
+
+use utils::{generation::Generation, id::TimelineId};
+
+#[derive(Serialize, Deserialize)]
+pub(super) struct HeatMapTenant {
+    /// Generation of the attached location that uploaded the heatmap: this is not required
+    /// for correctness, but acts as a hint to secondary locations in order to detect thrashing
+    /// in the unlikely event that two attached locations are both uploading conflicting heatmaps.
+    pub(super) generation: Generation,
+
+    pub(super) timelines: Vec<HeatMapTimeline>,
+}
+
+#[serde_as]
+#[derive(Serialize, Deserialize)]
+pub(crate) struct HeatMapTimeline {
+    #[serde_as(as = "DisplayFromStr")]
+    pub(super) timeline_id: TimelineId,
+
+    pub(super) layers: Vec<HeatMapLayer>,
+}
+
+#[serde_as]
+#[derive(Serialize, Deserialize)]
+pub(crate) struct HeatMapLayer {
+    pub(super) name: LayerFileName,
+    pub(super) metadata: IndexLayerMetadata,
+
+    #[serde_as(as = "TimestampSeconds<i64>")]
+    pub(super) access_time: SystemTime,
+    // TODO: an actual 'heat' score that would let secondary locations prioritize downloading
+    // the hottest layers, rather than trying to simply mirror whatever layers are on-disk on the primary.
+}
+
+impl HeatMapLayer {
+    pub(crate) fn new(
+        name: LayerFileName,
+        metadata: IndexLayerMetadata,
+        access_time: SystemTime,
+    ) -> Self {
+        Self {
+            name,
+            metadata,
+            access_time,
+        }
+    }
+}
+
+impl HeatMapTimeline {
+    pub(crate) fn new(timeline_id: TimelineId, layers: Vec<HeatMapLayer>) -> Self {
+        Self {
+            timeline_id,
+            layers,
+        }
+    }
+}

pageserver/src/tenant/secondary/heatmap_uploader.rs

@@ -0,0 +1,582 @@
+use std::{
+    collections::HashMap,
+    sync::{Arc, Weak},
+    time::{Duration, Instant},
+};
+
+use crate::{
+    metrics::SECONDARY_MODE,
+    tenant::{
+        config::AttachmentMode, mgr::TenantManager, remote_timeline_client::remote_heatmap_path,
+        secondary::CommandResponse, span::debug_assert_current_span_has_tenant_id, Tenant,
+    },
+};
+
+use md5;
+use pageserver_api::shard::TenantShardId;
+use remote_storage::GenericRemoteStorage;
+
+use tokio::task::JoinSet;
+use tokio_util::sync::CancellationToken;
+use tracing::instrument;
+use utils::{backoff, completion::Barrier};
+
+use super::{heatmap::HeatMapTenant, CommandRequest, UploadCommand};
+
+/// Period between heatmap uploader walking Tenants to look for work to do.
+/// If any tenants have a heatmap upload period lower than this, it will be adjusted
+/// downward to match.
+const DEFAULT_SCHEDULING_INTERVAL: Duration = Duration::from_millis(60000);
+const MIN_SCHEDULING_INTERVAL: Duration = Duration::from_millis(1000);
+
+struct WriteInProgress {
+    barrier: Barrier,
+}
+
+struct UploadPending {
+    tenant: Arc<Tenant>,
+    last_digest: Option<md5::Digest>,
+}
+
+struct WriteComplete {
+    tenant_shard_id: TenantShardId,
+    completed_at: Instant,
+    digest: Option<md5::Digest>,
+    next_upload: Option<Instant>,
+}
+
+/// The heatmap uploader keeps a little bit of per-tenant state, mainly to remember
+/// when we last did a write.  We only populate this after doing at least one
+/// write for a tenant -- this avoids holding state for tenants that have
+/// uploads disabled.
+
+struct UploaderTenantState {
+    // This Weak only exists to enable culling idle instances of this type
+    // when the Tenant has been deallocated.
+    tenant: Weak<Tenant>,
+
+    /// Digest of the serialized heatmap that we last successfully uploaded
+    ///
+    /// md5 is generally a bad hash.  We use it because it's convenient for interop with AWS S3's ETag,
+    /// which is also an md5sum.
+    last_digest: Option<md5::Digest>,
+
+    /// When the last upload attempt completed (may have been successful or failed)
+    last_upload: Option<Instant>,
+
+    /// When should we next do an upload?  None means never.
+    next_upload: Option<Instant>,
+}
+
+/// This type is owned by a single task ([`heatmap_uploader_task`]) which runs an event
+/// handling loop and mutates it as needed: there are no locks here, because that event loop
+/// can hold &mut references to this type throughout.
+struct HeatmapUploader {
+    tenant_manager: Arc<TenantManager>,
+    remote_storage: GenericRemoteStorage,
+    cancel: CancellationToken,
+
+    tenants: HashMap<TenantShardId, UploaderTenantState>,
+
+    /// Tenants with work to do, for which tasks should be spawned as soon as concurrency
+    /// limits permit it.
+    tenants_pending: std::collections::VecDeque<UploadPending>,
+
+    /// Tenants for which a task in `tasks` has been spawned.
+    tenants_uploading: HashMap<TenantShardId, WriteInProgress>,
+
+    tasks: JoinSet<()>,
+
+    /// Channel for our child tasks to send results to: we use a channel for results rather than
+    /// just getting task results via JoinSet because we need the channel's recv() "sleep until something
+    /// is available" semantic, rather than JoinSet::join_next()'s "sleep until next thing is available _or_ I'm empty"
+    /// behavior.
+    task_result_tx: tokio::sync::mpsc::UnboundedSender<WriteComplete>,
+    task_result_rx: tokio::sync::mpsc::UnboundedReceiver<WriteComplete>,
+
+    concurrent_uploads: usize,
+
+    scheduling_interval: Duration,
+}
+
+/// The uploader task runs a loop that periodically wakes up and schedules tasks for
+/// tenants that require an upload, or handles any commands that have been sent into
+/// `command_queue`.  No I/O is done in this loop: that all happens in the tasks we
+/// spawn.
+///
+/// Scheduling iterations are somewhat infrequent.  However, each one will enqueue
+/// all tenants that require an upload, and in between scheduling iterations we will
+/// continue to spawn new tasks for pending tenants, as our concurrency limit permits.
+///
+/// While we take a CancellationToken here, it is subordinate to the CancellationTokens
+/// of tenants: i.e. we expect all Tenants to have been shut down before we are shut down, otherwise
+/// we might block waiting on a Tenant.
+pub(super) async fn heatmap_uploader_task(
+    tenant_manager: Arc<TenantManager>,
+    remote_storage: GenericRemoteStorage,
+    mut command_queue: tokio::sync::mpsc::Receiver<CommandRequest<UploadCommand>>,
+    background_jobs_can_start: Barrier,
+    cancel: CancellationToken,
+) -> anyhow::Result<()> {
+    let concurrent_uploads = tenant_manager.get_conf().heatmap_upload_concurrency;
+
+    let (result_tx, result_rx) = tokio::sync::mpsc::unbounded_channel();
+
+    let mut uploader = HeatmapUploader {
+        tenant_manager,
+        remote_storage,
+        cancel: cancel.clone(),
+        tasks: JoinSet::new(),
+        tenants: HashMap::new(),
+        tenants_pending: std::collections::VecDeque::new(),
+        tenants_uploading: HashMap::new(),
+        task_result_tx: result_tx,
+        task_result_rx: result_rx,
+        concurrent_uploads,
+        scheduling_interval: DEFAULT_SCHEDULING_INTERVAL,
+    };
+
+    tracing::info!("Waiting for background_jobs_can start...");
+    background_jobs_can_start.wait().await;
+    tracing::info!("background_jobs_can is ready, proceeding.");
+
+    while !cancel.is_cancelled() {
+        // Look for new work: this is relatively expensive because we have to go acquire the lock on
+        // the tenant manager to retrieve tenants, and then iterate over them to figure out which ones
+        // require an upload.
+        uploader.schedule_iteration().await?;
+
+        // Between scheduling iterations, we will:
+        //  - Drain any complete tasks and spawn pending tasks
+        //  - Handle incoming administrative commands
+        //  - Check our cancellation token
+        let next_scheduling_iteration = Instant::now()
+            .checked_add(uploader.scheduling_interval)
+            .unwrap_or_else(|| {
+                tracing::warn!(
+                    "Scheduling interval invalid ({}s), running immediately!",
+                    uploader.scheduling_interval.as_secs_f64()
+                );
+                Instant::now()
+            });
+        loop {
+            tokio::select! {
+                _ = cancel.cancelled() => {
+                    // We do not simply drop the JoinSet, in order to have an orderly shutdown without cancellation.
+                    tracing::info!("Heatmap uploader joining tasks");
+                    while let Some(_r) = uploader.tasks.join_next().await {};
+                    tracing::info!("Heatmap uploader terminating");
+
+                    break;
+                },
+                _ = tokio::time::sleep(next_scheduling_iteration.duration_since(Instant::now())) => {
+                    tracing::debug!("heatmap_uploader_task: woke for scheduling interval");
+                    break;},
+                cmd = command_queue.recv() => {
+                    tracing::debug!("heatmap_uploader_task: woke for command queue");
+                    let cmd = match cmd {
+                        Some(c) =>c,
+                        None => {
+                            // SecondaryController was destroyed, and this has raced with
+                            // our CancellationToken
+                            tracing::info!("Heatmap uploader terminating");
+                            cancel.cancel();
+                            break;
+                        }
+                    };
+
+                    let CommandRequest{
+                        response_tx,
+                        payload
+                    } = cmd;
+                    uploader.handle_command(payload, response_tx);
+                },
+                _ = uploader.process_next_completion() => {
+                    if !cancel.is_cancelled() {
+                        uploader.spawn_pending();
+                    }
+                }
+            }
+        }
+    }
+
+    Ok(())
+}
+
+impl HeatmapUploader {
+    /// Periodic execution phase: inspect all attached tenants and schedule any work they require.
+    async fn schedule_iteration(&mut self) -> anyhow::Result<()> {
+        // Cull any entries in self.tenants whose Arc<Tenant> is gone
+        self.tenants
+            .retain(|_k, v| v.tenant.upgrade().is_some() && v.next_upload.is_some());
+
+        // The priority order of previously scheduled work may be invalidated by current state: drop
+        // all pending work (it will be re-scheduled if still needed)
+        self.tenants_pending.clear();
+
+        // Used a fixed 'now' through the following loop, for efficiency and fairness.
+        let now = Instant::now();
+
+        // While iterating over the potentially-long list of tenants, we will periodically yield
+        // to avoid blocking executor.
+        const YIELD_ITERATIONS: usize = 1000;
+
+        // Iterate over tenants looking for work to do.
+        let tenants = self.tenant_manager.get_attached_active_tenant_shards();
+        for (i, tenant) in tenants.into_iter().enumerate() {
+            // Process is shutting down, drop out
+            if self.cancel.is_cancelled() {
+                return Ok(());
+            }
+
+            // Skip tenants that already have a write in flight
+            if self
+                .tenants_uploading
+                .contains_key(tenant.get_tenant_shard_id())
+            {
+                continue;
+            }
+
+            self.maybe_schedule_upload(&now, tenant);
+
+            if i + 1 % YIELD_ITERATIONS == 0 {
+                tokio::task::yield_now().await;
+            }
+        }
+
+        // Spawn tasks for as many of our pending tenants as we can.
+        self.spawn_pending();
+
+        Ok(())
+    }
+
+    ///
+    /// Cancellation: this method is cancel-safe.
+    async fn process_next_completion(&mut self) {
+        match self.task_result_rx.recv().await {
+            Some(r) => {
+                self.on_completion(r);
+            }
+            None => {
+                unreachable!("Result sender is stored on Self");
+            }
+        }
+    }
+
+    /// The 'maybe' refers to the tenant's state: whether it is configured
+    /// for heatmap uploads at all, and whether sufficient time has passed
+    /// since the last upload.
+    fn maybe_schedule_upload(&mut self, now: &Instant, tenant: Arc<Tenant>) {
+        match tenant.get_heatmap_period() {
+            None => {
+                // Heatmaps are disabled for this tenant
+                return;
+            }
+            Some(period) => {
+                // If any tenant has asked for uploads more frequent than our scheduling interval,
+                // reduce it to match so that we can keep up.  This is mainly useful in testing, where
+                // we may set rather short intervals.
+                if period < self.scheduling_interval {
+                    self.scheduling_interval = std::cmp::max(period, MIN_SCHEDULING_INTERVAL);
+                }
+            }
+        }
+
+        // Stale attachments do not upload anything: if we are in this state, there is probably some
+        // other attachment in mode Single or Multi running on another pageserver, and we don't
+        // want to thrash and overwrite their heatmap uploads.
+        if tenant.get_attach_mode() == AttachmentMode::Stale {
+            return;
+        }
+
+        // Create an entry in self.tenants if one doesn't already exist: this will later be updated
+        // with the completion time in on_completion.
+        let state = self
+            .tenants
+            .entry(*tenant.get_tenant_shard_id())
+            .or_insert_with(|| UploaderTenantState {
+                tenant: Arc::downgrade(&tenant),
+                last_upload: None,
+                next_upload: Some(Instant::now()),
+                last_digest: None,
+            });
+
+        // Decline to do the upload if insufficient time has passed
+        if state.next_upload.map(|nu| &nu > now).unwrap_or(false) {
+            return;
+        }
+
+        let last_digest = state.last_digest;
+        self.tenants_pending.push_back(UploadPending {
+            tenant,
+            last_digest,
+        })
+    }
+
+    fn spawn_pending(&mut self) {
+        while !self.tenants_pending.is_empty()
+            && self.tenants_uploading.len() < self.concurrent_uploads
+        {
+            // unwrap: loop condition includes !is_empty()
+            let pending = self.tenants_pending.pop_front().unwrap();
+            self.spawn_upload(pending.tenant, pending.last_digest);
+        }
+    }
+
+    fn spawn_upload(&mut self, tenant: Arc<Tenant>, last_digest: Option<md5::Digest>) {
+        let remote_storage = self.remote_storage.clone();
+        let tenant_shard_id = *tenant.get_tenant_shard_id();
+        let (completion, barrier) = utils::completion::channel();
+        let result_tx = self.task_result_tx.clone();
+        self.tasks.spawn(async move {
+            // Guard for the barrier in [`WriteInProgress`]
+            let _completion = completion;
+
+            let started_at = Instant::now();
+            let digest = match upload_tenant_heatmap(remote_storage, &tenant, last_digest).await {
+                Ok(UploadHeatmapOutcome::Uploaded(digest)) => {
+                    let duration = Instant::now().duration_since(started_at);
+                    SECONDARY_MODE
+                        .upload_heatmap_duration
+                        .observe(duration.as_secs_f64());
+                    SECONDARY_MODE.upload_heatmap.inc();
+                    Some(digest)
+                }
+                Ok(UploadHeatmapOutcome::NoChange | UploadHeatmapOutcome::Skipped) => last_digest,
+                Err(UploadHeatmapError::Upload(e)) => {
+                    tracing::warn!(
+                        "Failed to upload heatmap for tenant {}: {e:#}",
+                        tenant.get_tenant_shard_id(),
+                    );
+                    let duration = Instant::now().duration_since(started_at);
+                    SECONDARY_MODE
+                        .upload_heatmap_duration
+                        .observe(duration.as_secs_f64());
+                    SECONDARY_MODE.upload_heatmap_errors.inc();
+                    last_digest
+                }
+                Err(UploadHeatmapError::Cancelled) => {
+                    tracing::info!("Cancelled heatmap upload, shutting down");
+                    last_digest
+                }
+            };
+
+            let now = Instant::now();
+            let next_upload = tenant
+                .get_heatmap_period()
+                .and_then(|period| now.checked_add(period));
+
+            result_tx
+                .send(WriteComplete {
+                    tenant_shard_id: *tenant.get_tenant_shard_id(),
+                    completed_at: now,
+                    digest,
+                    next_upload,
+                })
+                .ok();
+        });
+
+        self.tenants_uploading
+            .insert(tenant_shard_id, WriteInProgress { barrier });
+    }
+
+    #[instrument(skip_all, fields(tenant_id=%completion.tenant_shard_id.tenant_id, shard_id=%completion.tenant_shard_id.shard_slug()))]
+    fn on_completion(&mut self, completion: WriteComplete) {
+        tracing::debug!("Heatmap upload completed");
+        let WriteComplete {
+            tenant_shard_id,
+            completed_at,
+            digest,
+            next_upload,
+        } = completion;
+        self.tenants_uploading.remove(&tenant_shard_id);
+        use std::collections::hash_map::Entry;
+        match self.tenants.entry(tenant_shard_id) {
+            Entry::Vacant(_) => {
+                // Tenant state was dropped, nothing to update.
+            }
+            Entry::Occupied(mut entry) => {
+                entry.get_mut().last_upload = Some(completed_at);
+                entry.get_mut().last_digest = digest;
+                entry.get_mut().next_upload = next_upload
+            }
+        }
+    }
+
+    fn handle_command(
+        &mut self,
+        command: UploadCommand,
+        response_tx: tokio::sync::oneshot::Sender<CommandResponse>,
+    ) {
+        match command {
+            UploadCommand::Upload(tenant_shard_id) => {
+                // If an upload was ongoing for this tenant, let it finish first.
+                let barrier = if let Some(writing_state) =
+                    self.tenants_uploading.get(&tenant_shard_id)
+                {
+                    tracing::info!(
+                        tenant_id=%tenant_shard_id.tenant_id, shard_id=%tenant_shard_id.shard_slug(),
+                        "Waiting for heatmap write to complete");
+                    writing_state.barrier.clone()
+                } else {
+                    // Spawn the upload then immediately wait for it.  This will block processing of other commands and
+                    // starting of other background work.
+                    tracing::info!(
+                        tenant_id=%tenant_shard_id.tenant_id, shard_id=%tenant_shard_id.shard_slug(),
+                        "Starting heatmap write on command");
+                    let tenant = match self
+                        .tenant_manager
+                        .get_attached_tenant_shard(tenant_shard_id, true)
+                    {
+                        Ok(t) => t,
+                        Err(e) => {
+                            // Drop result of send: we don't care if caller dropped their receiver
+                            drop(response_tx.send(CommandResponse {
+                                result: Err(e.into()),
+                            }));
+                            return;
+                        }
+                    };
+                    self.spawn_upload(tenant, None);
+                    let writing_state = self
+                        .tenants_uploading
+                        .get(&tenant_shard_id)
+                        .expect("We just inserted this");
+                    tracing::info!(
+                        tenant_id=%tenant_shard_id.tenant_id, shard_id=%tenant_shard_id.shard_slug(),
+                        "Waiting for heatmap upload to complete");
+
+                    writing_state.barrier.clone()
+                };
+
+                // This task does no I/O: it only listens for a barrier's completion and then
+                // sends to the command response channel.  It is therefore safe to spawn this without
+                // any gates/task_mgr hooks.
+                tokio::task::spawn(async move {
+                    barrier.wait().await;
+
+                    tracing::info!(
+                        tenant_id=%tenant_shard_id.tenant_id, shard_id=%tenant_shard_id.shard_slug(),
+                        "Heatmap upload complete");
+
+                    // Drop result of send: we don't care if caller dropped their receiver
+                    drop(response_tx.send(CommandResponse { result: Ok(()) }))
+                });
+            }
+        }
+    }
+}
+
+enum UploadHeatmapOutcome {
+    /// We successfully wrote to remote storage, with this digest.
+    Uploaded(md5::Digest),
+    /// We did not upload because the heatmap digest was unchanged since the last upload
+    NoChange,
+    /// We skipped the upload for some reason, such as tenant/timeline not ready
+    Skipped,
+}
+
+#[derive(thiserror::Error, Debug)]
+enum UploadHeatmapError {
+    #[error("Cancelled")]
+    Cancelled,
+
+    #[error(transparent)]
+    Upload(#[from] anyhow::Error),
+}
+
+/// The inner upload operation.  This will skip if `last_digest` is Some and matches the digest
+/// of the object we would have uploaded.
+#[instrument(skip_all, fields(tenant_id = %tenant.get_tenant_shard_id().tenant_id, shard_id = %tenant.get_tenant_shard_id().shard_slug()))]
+async fn upload_tenant_heatmap(
+    remote_storage: GenericRemoteStorage,
+    tenant: &Arc<Tenant>,
+    last_digest: Option<md5::Digest>,
+) -> Result<UploadHeatmapOutcome, UploadHeatmapError> {
+    debug_assert_current_span_has_tenant_id();
+
+    let generation = tenant.get_generation();
+    if generation.is_none() {
+        // We do not expect this: generations were implemented before heatmap uploads.  However,
+        // handle it so that we don't have to make the generation in the heatmap an Option<>
+        // (Generation::none is not serializable)
+        tracing::warn!("Skipping heatmap upload for tenant with generation==None");
+        return Ok(UploadHeatmapOutcome::Skipped);
+    }
+
+    let mut heatmap = HeatMapTenant {
+        timelines: Vec::new(),
+        generation,
+    };
+    let timelines = tenant.timelines.lock().unwrap().clone();
+
+    let tenant_cancel = tenant.cancel.clone();
+
+    // Ensure that Tenant::shutdown waits for any upload in flight: this is needed because otherwise
+    // when we delete a tenant, we might race with an upload in flight and end up leaving a heatmap behind
+    // in remote storage.
+    let _guard = match tenant.gate.enter() {
+        Ok(g) => g,
+        Err(_) => {
+            tracing::info!("Skipping heatmap upload for tenant which is shutting down");
+            return Err(UploadHeatmapError::Cancelled);
+        }
+    };
+
+    for (timeline_id, timeline) in timelines {
+        let heatmap_timeline = timeline.generate_heatmap().await;
+        match heatmap_timeline {
+            None => {
+                tracing::debug!(
+                    "Skipping heatmap upload because timeline {timeline_id} is not ready"
+                );
+                return Ok(UploadHeatmapOutcome::Skipped);
+            }
+            Some(heatmap_timeline) => {
+                heatmap.timelines.push(heatmap_timeline);
+            }
+        }
+    }
+
+    // Serialize the heatmap
+    let bytes = serde_json::to_vec(&heatmap).map_err(|e| anyhow::anyhow!(e))?;
+    let size = bytes.len();
+
+    // Drop out early if nothing changed since our last upload
+    let digest = md5::compute(&bytes);
+    if Some(digest) == last_digest {
+        return Ok(UploadHeatmapOutcome::NoChange);
+    }
+
+    let path = remote_heatmap_path(tenant.get_tenant_shard_id());
+
+    // Write the heatmap.
+    tracing::debug!("Uploading {size} byte heatmap to {path}");
+    if let Err(e) = backoff::retry(
+        || async {
+            let bytes = futures::stream::once(futures::future::ready(Ok(bytes::Bytes::from(
+                bytes.clone(),
+            ))));
+            remote_storage
+                .upload_storage_object(bytes, size, &path)
+                .await
+        },
+        |_| false,
+        3,
+        u32::MAX,
+        "Uploading heatmap",
+        backoff::Cancel::new(tenant_cancel.clone(), || anyhow::anyhow!("Shutting down")),
+    )
+    .await
+    {
+        if tenant_cancel.is_cancelled() {
+            return Err(UploadHeatmapError::Cancelled);
+        } else {
+            return Err(e.into());
+        }
+    }
+
+    tracing::info!("Successfully uploaded {size} byte heatmap to {path}");
+
+    Ok(UploadHeatmapOutcome::Uploaded(digest))
+}

pageserver/src/tenant/storage_layer/layer.rs

@@ -457,6 +457,8 @@ struct LayerInner {
     /// For loaded layers, this may be some other value if the tenant has undergone
     /// a shard split since the layer was originally written.
     shard: ShardIndex,
+
+    last_evicted_at: std::sync::Mutex<Option<std::time::Instant>>,
 }
 
 impl std::fmt::Display for LayerInner {
@@ -587,6 +589,7 @@ impl LayerInner {
             consecutive_failures: AtomicUsize::new(0),
             generation,
             shard,
+            last_evicted_at: std::sync::Mutex::default(),
         }
     }
 
@@ -722,6 +725,14 @@ impl LayerInner {
                     permit
                 };
 
+                let since_last_eviction =
+                    self.last_evicted_at.lock().unwrap().map(|ts| ts.elapsed());
+                if let Some(since_last_eviction) = since_last_eviction {
+                    // FIXME: this will not always be recorded correctly until #6028 (the no
+                    // download needed branch above)
+                    LAYER_IMPL_METRICS.record_redownloaded_after(since_last_eviction);
+                }
+
                 let res = Arc::new(DownloadedLayer {
                     owner: Arc::downgrade(self),
                     kind: tokio::sync::OnceCell::default(),
@@ -1117,6 +1128,8 @@ impl LayerInner {
         // we are still holding the permit, so no new spawn_download_and_wait can happen
         drop(self.status.send(Status::Evicted));
 
+        *self.last_evicted_at.lock().unwrap() = Some(std::time::Instant::now());
+
         res
     }
 
@@ -1421,6 +1434,7 @@ pub(crate) struct LayerImplMetrics {
 
     rare_counters: enum_map::EnumMap<RareEvent, IntCounter>,
     inits_cancelled: metrics::core::GenericCounter<metrics::core::AtomicU64>,
+    redownload_after: metrics::Histogram,
 }
 
 impl Default for LayerImplMetrics {
@@ -1496,6 +1510,26 @@ impl Default for LayerImplMetrics {
         )
         .unwrap();
 
+        let redownload_after = {
+            let minute = 60.0;
+            let hour = 60.0 * minute;
+            metrics::register_histogram!(
+                "pageserver_layer_redownloaded_after",
+                "Time between evicting and re-downloading.",
+                vec![
+                    10.0,
+                    30.0,
+                    minute,
+                    5.0 * minute,
+                    15.0 * minute,
+                    30.0 * minute,
+                    hour,
+                    12.0 * hour,
+                ]
+            )
+            .unwrap()
+        };
+
         Self {
             started_evictions,
             completed_evictions,
@@ -1507,6 +1541,7 @@ impl Default for LayerImplMetrics {
 
             rare_counters,
             inits_cancelled,
+            redownload_after,
         }
     }
 }
@@ -1574,6 +1609,10 @@ impl LayerImplMetrics {
     fn inc_init_cancelled(&self) {
         self.inits_cancelled.inc()
     }
+
+    fn record_redownloaded_after(&self, duration: std::time::Duration) {
+        self.redownload_after.observe(duration.as_secs_f64())
+    }
 }
 
 #[derive(enum_map::Enum)]

pageserver/src/tenant/tasks.rs

@@ -63,12 +63,10 @@ pub(crate) async fn concurrent_background_tasks_rate_limit(
     _ctx: &RequestContext,
     cancel: &CancellationToken,
 ) -> Result<impl Drop, RateLimitError> {
-    crate::metrics::BACKGROUND_LOOP_SEMAPHORE_WAIT_START_COUNT
+    let _guard = crate::metrics::BACKGROUND_LOOP_SEMAPHORE_WAIT_GAUGE
         .with_label_values(&[loop_kind.as_static_str()])
-        .inc();
-    scopeguard::defer!(
-        crate::metrics::BACKGROUND_LOOP_SEMAPHORE_WAIT_FINISH_COUNT.with_label_values(&[loop_kind.as_static_str()]).inc();
-    );
+        .guard();
+
     tokio::select! {
         permit = CONCURRENT_BACKGROUND_TASKS.acquire() => {
             match permit {

pageserver/src/tenant/timeline.rs

@@ -29,7 +29,7 @@ use tokio::{
 };
 use tokio_util::sync::CancellationToken;
 use tracing::*;
-use utils::{id::TenantTimelineId, sync::gate::Gate};
+use utils::sync::gate::Gate;
 
 use std::collections::{BinaryHeap, HashMap, HashSet};
 use std::ops::{Deref, Range};
@@ -98,8 +98,9 @@ use self::logical_size::LogicalSize;
 use self::walreceiver::{WalReceiver, WalReceiverConf};
 
 use super::config::TenantConf;
-use super::remote_timeline_client::index::IndexPart;
+use super::remote_timeline_client::index::{IndexLayerMetadata, IndexPart};
 use super::remote_timeline_client::RemoteTimelineClient;
+use super::secondary::heatmap::{HeatMapLayer, HeatMapTimeline};
 use super::{debug_assert_current_span_has_tenant_and_timeline_id, AttachedTenantConf};
 
 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
@@ -377,9 +378,6 @@ pub enum PageReconstructError {
     #[error(transparent)]
     Other(#[from] anyhow::Error),
 
-    /// The operation would require downloading a layer that is missing locally.
-    NeedsDownload(TenantTimelineId, LayerFileName),
-
     /// The operation was cancelled
     Cancelled,
 
@@ -408,14 +406,6 @@ impl std::fmt::Debug for PageReconstructError {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
         match self {
             Self::Other(err) => err.fmt(f),
-            Self::NeedsDownload(tenant_timeline_id, layer_file_name) => {
-                write!(
-                    f,
-                    "layer {}/{} needs download",
-                    tenant_timeline_id,
-                    layer_file_name.file_name()
-                )
-            }
             Self::Cancelled => write!(f, "cancelled"),
             Self::AncestorStopping(timeline_id) => {
                 write!(f, "ancestor timeline {timeline_id} is being stopped")
@@ -429,14 +419,6 @@ impl std::fmt::Display for PageReconstructError {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
         match self {
             Self::Other(err) => err.fmt(f),
-            Self::NeedsDownload(tenant_timeline_id, layer_file_name) => {
-                write!(
-                    f,
-                    "layer {}/{} needs download",
-                    tenant_timeline_id,
-                    layer_file_name.file_name()
-                )
-            }
             Self::Cancelled => write!(f, "cancelled"),
             Self::AncestorStopping(timeline_id) => {
                 write!(f, "ancestor timeline {timeline_id} is being stopped")
@@ -464,6 +446,12 @@ pub(crate) enum CompactFlags {
     ForceRepartition,
 }
 
+impl std::fmt::Debug for Timeline {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "Timeline<{}>", self.timeline_id)
+    }
+}
+
 /// Public interface functions
 impl Timeline {
     /// Get the LSN where this branch was created
@@ -1118,8 +1106,9 @@ impl Timeline {
         Ok(Some(true))
     }
 
-    /// Like [`evict_layer_batch`](Self::evict_layer_batch), but for just one layer.
-    /// Additional case `Ok(None)` covers the case where the layer could not be found by its `layer_file_name`.
+    /// Evict just one layer.
+    ///
+    /// Returns `Ok(None)` in the case where the layer could not be found by its `layer_file_name`.
     pub async fn evict_layer(&self, layer_file_name: &str) -> anyhow::Result<Option<bool>> {
         let _gate = self
             .gate
@@ -1130,109 +1119,17 @@ impl Timeline {
             return Ok(None);
         };
 
-        let Some(local_layer) = local_layer.keep_resident().await? else {
-            return Ok(Some(false));
-        };
-
-        let local_layer: Layer = local_layer.into();
-
-        let remote_client = self
+        let rtc = self
             .remote_client
             .as_ref()
             .ok_or_else(|| anyhow::anyhow!("remote storage not configured; cannot evict"))?;
 
-        let results = self
-            .evict_layer_batch(remote_client, &[local_layer])
-            .await?;
-        assert_eq!(results.len(), 1);
-        let result: Option<Result<(), EvictionError>> = results.into_iter().next().unwrap();
-        match result {
-            None => anyhow::bail!("task_mgr shutdown requested"),
-            Some(Ok(())) => Ok(Some(true)),
-            Some(Err(e)) => Err(anyhow::Error::new(e)),
+        match local_layer.evict_and_wait(rtc).await {
+            Ok(()) => Ok(Some(true)),
+            Err(EvictionError::NotFound) => Ok(Some(false)),
+            Err(EvictionError::Downloaded) => Ok(Some(false)),
         }
     }
-
-    /// Evict a batch of layers.
-    pub(crate) async fn evict_layers(
-        &self,
-        layers_to_evict: &[Layer],
-    ) -> anyhow::Result<Vec<Option<Result<(), EvictionError>>>> {
-        let _gate = self
-            .gate
-            .enter()
-            .map_err(|_| anyhow::anyhow!("Shutting down"))?;
-
-        let remote_client = self
-            .remote_client
-            .as_ref()
-            .context("timeline must have RemoteTimelineClient")?;
-
-        self.evict_layer_batch(remote_client, layers_to_evict).await
-    }
-
-    /// Evict multiple layers at once, continuing through errors.
-    ///
-    /// The `remote_client` should be this timeline's `self.remote_client`.
-    /// We make the caller provide it so that they are responsible for handling the case
-    /// where someone wants to evict the layer but no remote storage is configured.
-    ///
-    /// Returns either `Err()` or `Ok(results)` where `results.len() == layers_to_evict.len()`.
-    /// If `Err()` is returned, no eviction was attempted.
-    /// Each position of `Ok(results)` corresponds to the layer in `layers_to_evict`.
-    /// Meaning of each `result[i]`:
-    /// - `Some(Err(...))` if layer replacement failed for some reason
-    ///    - replacement failed for an expectable reason (e.g., layer removed by GC before we grabbed all locks)
-    /// - `Some(Ok(()))` if everything went well.
-    /// - `None` if no eviction attempt was made for the layer because `cancel.is_cancelled() == true`.
-    async fn evict_layer_batch(
-        &self,
-        remote_client: &Arc<RemoteTimelineClient>,
-        layers_to_evict: &[Layer],
-    ) -> anyhow::Result<Vec<Option<Result<(), EvictionError>>>> {
-        {
-            // to avoid racing with detach and delete_timeline
-            let state = self.current_state();
-            anyhow::ensure!(
-                state == TimelineState::Active,
-                "timeline is not active but {state:?}"
-            );
-        }
-
-        let mut results = Vec::with_capacity(layers_to_evict.len());
-        for _ in 0..layers_to_evict.len() {
-            results.push(None);
-        }
-
-        let mut js = tokio::task::JoinSet::new();
-
-        for (i, l) in layers_to_evict.iter().enumerate() {
-            js.spawn({
-                let l = l.to_owned();
-                let remote_client = remote_client.clone();
-                async move { (i, l.evict_and_wait(&remote_client).await) }
-            });
-        }
-
-        let join = async {
-            while let Some(next) = js.join_next().await {
-                match next {
-                    Ok((i, res)) => results[i] = Some(res),
-                    Err(je) if je.is_cancelled() => unreachable!("not used"),
-                    Err(je) if je.is_panic() => { /* already logged */ }
-                    Err(je) => tracing::error!("unknown JoinError: {je:?}"),
-                }
-            }
-        };
-
-        tokio::select! {
-            _ = self.cancel.cancelled() => {},
-            _ = join => {}
-        }
-
-        assert_eq!(results.len(), layers_to_evict.len());
-        Ok(results)
-    }
 }
 
 /// Number of times we will compute partition within a checkpoint distance.
@@ -2165,6 +2062,55 @@ impl Timeline {
 
         None
     }
+
+    /// The timeline heatmap is a hint to secondary locations from the primary location,
+    /// indicating which layers are currently on-disk on the primary.
+    ///
+    /// None is returned if the Timeline is in a state where uploading a heatmap
+    /// doesn't make sense, such as shutting down or initializing.  The caller
+    /// should treat this as a cue to simply skip doing any heatmap uploading
+    /// for this timeline.
+    pub(crate) async fn generate_heatmap(&self) -> Option<HeatMapTimeline> {
+        let eviction_info = self.get_local_layers_for_disk_usage_eviction().await;
+
+        let remote_client = match &self.remote_client {
+            Some(c) => c,
+            None => return None,
+        };
+
+        let layer_file_names = eviction_info
+            .resident_layers
+            .iter()
+            .map(|l| l.layer.layer_desc().filename())
+            .collect::<Vec<_>>();
+
+        let decorated = match remote_client.get_layers_metadata(layer_file_names) {
+            Ok(d) => d,
+            Err(_) => {
+                // Getting metadata only fails on Timeline in bad state.
+                return None;
+            }
+        };
+
+        let heatmap_layers = std::iter::zip(
+            eviction_info.resident_layers.into_iter(),
+            decorated.into_iter(),
+        )
+        .filter_map(|(layer, remote_info)| {
+            remote_info.map(|remote_info| {
+                HeatMapLayer::new(
+                    layer.layer.layer_desc().filename(),
+                    IndexLayerMetadata::from(remote_info),
+                    layer.last_activity_ts,
+                )
+            })
+        });
+
+        Some(HeatMapTimeline::new(
+            self.timeline_id,
+            heatmap_layers.collect(),
+        ))
+    }
 }
 
 type TraversalId = String;
@@ -4605,7 +4551,7 @@ mod tests {
             .await
             .unwrap();
 
-        let rc = timeline
+        let rtc = timeline
             .remote_client
             .clone()
             .expect("just configured this");
@@ -4618,16 +4564,12 @@ mod tests {
             .expect("should had been resident")
             .drop_eviction_guard();
 
-        let batch = [layer];
-
-        let first = async { timeline.evict_layer_batch(&rc, &batch).await.unwrap() };
-        let second = async { timeline.evict_layer_batch(&rc, &batch).await.unwrap() };
+        let first = async { layer.evict_and_wait(&rtc).await };
+        let second = async { layer.evict_and_wait(&rtc).await };
 
         let (first, second) = tokio::join!(first, second);
 
-        let (first, second) = (only_one(first), only_one(second));
-
-        let res = batch[0].keep_resident().await;
+        let res = layer.keep_resident().await;
         assert!(matches!(res, Ok(None)), "{res:?}");
 
         match (first, second) {
@@ -4648,14 +4590,6 @@ mod tests {
         RequestContext::new(TaskKind::UnitTest, DownloadBehavior::Error)
     }
 
-    fn only_one<T>(mut input: Vec<Option<T>>) -> T {
-        assert_eq!(1, input.len());
-        input
-            .pop()
-            .expect("length just checked")
-            .expect("no cancellation")
-    }
-
     async fn find_some_layer(timeline: &Timeline) -> Layer {
         let layers = timeline.layers.read().await;
         let desc = layers

pageserver/src/tenant/timeline/eviction_task.rs

@@ -212,11 +212,21 @@ impl Timeline {
         // Gather layers for eviction.
         // NB: all the checks can be invalidated as soon as we release the layer map lock.
         // We don't want to hold the layer map lock during eviction.
+
         // So, we just need to deal with this.
-        let candidates: Vec<_> = {
+
+        let remote_client = match self.remote_client.as_ref() {
+            Some(c) => c,
+            None => {
+                error!("no remote storage configured, cannot evict layers");
+                return ControlFlow::Continue(());
+            }
+        };
+
+        let mut js = tokio::task::JoinSet::new();
+        {
             let guard = self.layers.read().await;
             let layers = guard.layer_map();
-            let mut candidates = Vec::new();
             for hist_layer in layers.iter_historic_layers() {
                 let hist_layer = guard.get_from_desc(&hist_layer);
 
@@ -262,54 +272,49 @@ impl Timeline {
                         continue;
                     }
                 };
+                let layer = guard.drop_eviction_guard();
                 if no_activity_for > p.threshold {
-                    candidates.push(guard.drop_eviction_guard())
+                    let remote_client = remote_client.clone();
+                    // this could cause a lot of allocations in some cases
+                    js.spawn(async move { layer.evict_and_wait(&remote_client).await });
+                    stats.candidates += 1;
                 }
             }
-            candidates
-        };
-        stats.candidates = candidates.len();
-
-        let remote_client = match self.remote_client.as_ref() {
-            None => {
-                error!(
-                    num_candidates = candidates.len(),
-                    "no remote storage configured, cannot evict layers"
-                );
-                return ControlFlow::Continue(());
-            }
-            Some(c) => c,
         };
 
-        let results = match self.evict_layer_batch(remote_client, &candidates).await {
-            Err(pre_err) => {
-                stats.errors += candidates.len();
-                error!("could not do any evictions: {pre_err:#}");
-                return ControlFlow::Continue(());
+        let join_all = async move {
+            while let Some(next) = js.join_next().await {
+                match next {
+                    Ok(Ok(())) => stats.evicted += 1,
+                    Ok(Err(EvictionError::NotFound | EvictionError::Downloaded)) => {
+                        stats.not_evictable += 1;
+                    }
+                    Err(je) if je.is_cancelled() => unreachable!("not used"),
+                    Err(je) if je.is_panic() => {
+                        /* already logged */
+                        stats.errors += 1;
+                    }
+                    Err(je) => tracing::error!("unknown JoinError: {je:?}"),
+                }
             }
-            Ok(results) => results,
+            stats
         };
-        assert_eq!(results.len(), candidates.len());
-        for result in results {
-            match result {
-                None => {
-                    stats.skipped_for_shutdown += 1;
-                }
-                Some(Ok(())) => {
-                    stats.evicted += 1;
-                }
-                Some(Err(EvictionError::NotFound | EvictionError::Downloaded)) => {
-                    stats.not_evictable += 1;
+
+        tokio::select! {
+            stats = join_all => {
+                if stats.candidates == stats.not_evictable {
+                    debug!(stats=?stats, "eviction iteration complete");
+                } else if stats.errors > 0 || stats.not_evictable > 0 {
+                    warn!(stats=?stats, "eviction iteration complete");
+                } else {
+                    info!(stats=?stats, "eviction iteration complete");
                 }
             }
+            _ = cancel.cancelled() => {
+                // just drop the joinset to "abort"
+            }
         }
-        if stats.candidates == stats.not_evictable {
-            debug!(stats=?stats, "eviction iteration complete");
-        } else if stats.errors > 0 || stats.not_evictable > 0 {
-            warn!(stats=?stats, "eviction iteration complete");
-        } else {
-            info!(stats=?stats, "eviction iteration complete");
-        }
+
         ControlFlow::Continue(())
     }
 

pageserver/src/tenant/timeline/uninit.rs

@@ -19,14 +19,14 @@ use super::Timeline;
 pub struct UninitializedTimeline<'t> {
     pub(crate) owning_tenant: &'t Tenant,
     timeline_id: TimelineId,
-    raw_timeline: Option<(Arc<Timeline>, TimelineUninitMark)>,
+    raw_timeline: Option<(Arc<Timeline>, TimelineUninitMark<'t>)>,
 }
 
 impl<'t> UninitializedTimeline<'t> {
     pub(crate) fn new(
         owning_tenant: &'t Tenant,
         timeline_id: TimelineId,
-        raw_timeline: Option<(Arc<Timeline>, TimelineUninitMark)>,
+        raw_timeline: Option<(Arc<Timeline>, TimelineUninitMark<'t>)>,
     ) -> Self {
         Self {
             owning_tenant,
@@ -169,18 +169,55 @@ pub(crate) fn cleanup_timeline_directory(uninit_mark: TimelineUninitMark) {
 ///
 /// XXX: it's important to create it near the timeline dir, not inside it to ensure timeline dir gets removed first.
 #[must_use]
-pub(crate) struct TimelineUninitMark {
+pub(crate) struct TimelineUninitMark<'t> {
+    owning_tenant: &'t Tenant,
+    timeline_id: TimelineId,
     uninit_mark_deleted: bool,
     uninit_mark_path: Utf8PathBuf,
     pub(crate) timeline_path: Utf8PathBuf,
 }
 
-impl TimelineUninitMark {
-    pub(crate) fn new(uninit_mark_path: Utf8PathBuf, timeline_path: Utf8PathBuf) -> Self {
-        Self {
-            uninit_mark_deleted: false,
-            uninit_mark_path,
-            timeline_path,
+/// Errors when acquiring exclusive access to a timeline ID for creation
+#[derive(thiserror::Error, Debug)]
+pub(crate) enum TimelineExclusionError {
+    #[error("Already exists")]
+    AlreadyExists(Arc<Timeline>),
+    #[error("Already creating")]
+    AlreadyCreating,
+
+    // e.g. I/O errors, or some failure deep in postgres initdb
+    #[error(transparent)]
+    Other(#[from] anyhow::Error),
+}
+
+impl<'t> TimelineUninitMark<'t> {
+    pub(crate) fn new(
+        owning_tenant: &'t Tenant,
+        timeline_id: TimelineId,
+        uninit_mark_path: Utf8PathBuf,
+        timeline_path: Utf8PathBuf,
+    ) -> Result<Self, TimelineExclusionError> {
+        // Lock order: this is the only place we take both locks.  During drop() we only
+        // lock creating_timelines
+        let timelines = owning_tenant.timelines.lock().unwrap();
+        let mut creating_timelines: std::sync::MutexGuard<
+            '_,
+            std::collections::HashSet<TimelineId>,
+        > = owning_tenant.timelines_creating.lock().unwrap();
+
+        if let Some(existing) = timelines.get(&timeline_id) {
+            Err(TimelineExclusionError::AlreadyExists(existing.clone()))
+        } else if creating_timelines.contains(&timeline_id) {
+            Err(TimelineExclusionError::AlreadyCreating)
+        } else {
+            creating_timelines.insert(timeline_id);
+            Ok(Self {
+                owning_tenant,
+                timeline_id,
+                uninit_mark_deleted: false,
+                uninit_mark_path,
+                timeline_path,
+            })
         }
     }
 
@@ -207,7 +244,7 @@ impl TimelineUninitMark {
     }
 }
 
-impl Drop for TimelineUninitMark {
+impl Drop for TimelineUninitMark<'_> {
     fn drop(&mut self) {
         if !self.uninit_mark_deleted {
             if self.timeline_path.exists() {
@@ -226,5 +263,11 @@ impl Drop for TimelineUninitMark {
                 }
             }
         }
+
+        self.owning_tenant
+            .timelines_creating
+            .lock()
+            .unwrap()
+            .remove(&self.timeline_id);
     }
 }

pageserver/src/walingest.rs

@@ -2191,7 +2191,7 @@ mod tests {
             .load()
             .await;
         let tline = tenant
-            .bootstrap_timeline(TIMELINE_ID, pg_version, None, &ctx)
+            .bootstrap_timeline_test(TIMELINE_ID, pg_version, None, &ctx)
             .await
             .unwrap();