pageserver: basebackup cache (hackathon project) (#11989)

## Problem
Basebackup cache is on the hot path of compute startup and is generated
on every request (may be slow).

- Issue: https://github.com/neondatabase/cloud/issues/29353

## Summary of changes
- Add `BasebackupCache` which stores basebackups on local disk.
- Basebackup prepare requests are triggered by
`XLOG_CHECKPOINT_SHUTDOWN` records in the log.
- Limit the size of the cache by number of entries.
- Add `basebackup_cache_enabled` feature flag to TenantConfig.
- Write tests for the cache

## Not implemented yet
- Limit the size of the cache by total size in bytes

---------

Co-authored-by: Aleksandr Sarantsev <aleksandr@neon.tech>

control_plane/src/pageserver.rs

@@ -551,6 +551,11 @@ impl PageServerNode {
                 .map(|x| x.parse::<usize>())
                 .transpose()
                 .context("Falied to parse 'relsize_snapshot_cache_capacity' as integer")?,
+            basebackup_cache_enabled: settings
+                .remove("basebackup_cache_enabled")
+                .map(|x| x.parse::<bool>())
+                .transpose()
+                .context("Failed to parse 'basebackup_cache_enabled' as bool")?,
         };
         if !settings.is_empty() {
             bail!("Unrecognized tenant settings: {settings:?}")

libs/pageserver_api/src/config.rs

@@ -183,6 +183,8 @@ pub struct ConfigToml {
     pub enable_tls_page_service_api: bool,
     pub dev_mode: bool,
     pub timeline_import_config: TimelineImportConfig,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub basebackup_cache_config: Option<BasebackupCacheConfig>,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
@@ -308,6 +310,26 @@ pub struct TimelineImportConfig {
     pub import_job_checkpoint_threshold: NonZeroUsize,
 }
 
+#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+#[serde(default)]
+pub struct BasebackupCacheConfig {
+    #[serde(with = "humantime_serde")]
+    pub cleanup_period: Duration,
+    // FIXME: Support max_size_bytes.
+    // pub max_size_bytes: usize,
+    pub max_size_entries: i64,
+}
+
+impl Default for BasebackupCacheConfig {
+    fn default() -> Self {
+        Self {
+            cleanup_period: Duration::from_secs(60),
+            // max_size_bytes: 1024 * 1024 * 1024, // 1 GiB
+            max_size_entries: 1000,
+        }
+    }
+}
+
 pub mod statvfs {
     pub mod mock {
         #[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
@@ -491,8 +513,14 @@ pub struct TenantConfigToml {
     /// Tenant level performance sampling ratio override. Controls the ratio of get page requests
     /// that will get perf sampling for the tenant.
     pub sampling_ratio: Option<Ratio>,
+
     /// Capacity of relsize snapshot cache (used by replicas).
     pub relsize_snapshot_cache_capacity: usize,
+
+    /// Enable preparing basebackup on XLOG_CHECKPOINT_SHUTDOWN and using it in basebackup requests.
+    // FIXME: Remove skip_serializing_if when the feature is stable.
+    #[serde(skip_serializing_if = "std::ops::Not::not")]
+    pub basebackup_cache_enabled: bool,
 }
 
 pub mod defaults {
@@ -666,6 +694,7 @@ impl Default for ConfigToml {
                 import_job_soft_size_limit: NonZeroUsize::new(1024 * 1024 * 1024).unwrap(),
                 import_job_checkpoint_threshold: NonZeroUsize::new(128).unwrap(),
             },
+            basebackup_cache_config: None,
         }
     }
 }
@@ -791,6 +820,7 @@ impl Default for TenantConfigToml {
             gc_compaction_ratio_percent: DEFAULT_GC_COMPACTION_RATIO_PERCENT,
             sampling_ratio: None,
             relsize_snapshot_cache_capacity: DEFAULT_RELSIZE_SNAPSHOT_CACHE_CAPACITY,
+            basebackup_cache_enabled: false,
         }
     }
 }

libs/pageserver_api/src/models.rs

@@ -632,6 +632,8 @@ pub struct TenantConfigPatch {
     pub sampling_ratio: FieldPatch<Option<Ratio>>,
     #[serde(skip_serializing_if = "FieldPatch::is_noop")]
     pub relsize_snapshot_cache_capacity: FieldPatch<usize>,
+    #[serde(skip_serializing_if = "FieldPatch::is_noop")]
+    pub basebackup_cache_enabled: FieldPatch<bool>,
 }
 
 /// Like [`crate::config::TenantConfigToml`], but preserves the information
@@ -764,6 +766,9 @@ pub struct TenantConfig {
 
     #[serde(skip_serializing_if = "Option::is_none")]
     pub relsize_snapshot_cache_capacity: Option<usize>,
+
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub basebackup_cache_enabled: Option<bool>,
 }
 
 impl TenantConfig {
@@ -810,6 +815,7 @@ impl TenantConfig {
             mut gc_compaction_ratio_percent,
             mut sampling_ratio,
             mut relsize_snapshot_cache_capacity,
+            mut basebackup_cache_enabled,
         } = self;
 
         patch.checkpoint_distance.apply(&mut checkpoint_distance);
@@ -914,6 +920,9 @@ impl TenantConfig {
         patch
             .relsize_snapshot_cache_capacity
             .apply(&mut relsize_snapshot_cache_capacity);
+        patch
+            .basebackup_cache_enabled
+            .apply(&mut basebackup_cache_enabled);
 
         Ok(Self {
             checkpoint_distance,
@@ -954,6 +963,7 @@ impl TenantConfig {
             gc_compaction_ratio_percent,
             sampling_ratio,
             relsize_snapshot_cache_capacity,
+            basebackup_cache_enabled,
         })
     }
 
@@ -1065,6 +1075,9 @@ impl TenantConfig {
             relsize_snapshot_cache_capacity: self
                 .relsize_snapshot_cache_capacity
                 .unwrap_or(global_conf.relsize_snapshot_cache_capacity),
+            basebackup_cache_enabled: self
+                .basebackup_cache_enabled
+                .unwrap_or(global_conf.basebackup_cache_enabled),
         }
     }
 }

pageserver/src/basebackup_cache.rs

@@ -0,0 +1,518 @@
+use std::{collections::HashMap, sync::Arc};
+
+use async_compression::tokio::write::GzipEncoder;
+use camino::{Utf8Path, Utf8PathBuf};
+use metrics::core::{AtomicU64, GenericCounter};
+use pageserver_api::{config::BasebackupCacheConfig, models::TenantState};
+use tokio::{
+    io::{AsyncWriteExt, BufWriter},
+    sync::mpsc::{UnboundedReceiver, UnboundedSender},
+};
+use tokio_util::sync::CancellationToken;
+use utils::{
+    id::{TenantId, TenantTimelineId, TimelineId},
+    lsn::Lsn,
+    shard::TenantShardId,
+};
+
+use crate::{
+    basebackup::send_basebackup_tarball,
+    context::{DownloadBehavior, RequestContext},
+    metrics::{BASEBACKUP_CACHE_ENTRIES, BASEBACKUP_CACHE_PREPARE, BASEBACKUP_CACHE_READ},
+    task_mgr::TaskKind,
+    tenant::{
+        Timeline,
+        mgr::{TenantManager, TenantSlot},
+    },
+};
+
+pub struct BasebackupPrepareRequest {
+    pub tenant_shard_id: TenantShardId,
+    pub timeline_id: TimelineId,
+    pub lsn: Lsn,
+}
+
+pub type BasebackupPrepareSender = UnboundedSender<BasebackupPrepareRequest>;
+pub type BasebackupPrepareReceiver = UnboundedReceiver<BasebackupPrepareRequest>;
+
+type BasebackupRemoveEntrySender = UnboundedSender<Utf8PathBuf>;
+type BasebackupRemoveEntryReceiver = UnboundedReceiver<Utf8PathBuf>;
+
+/// BasebackupCache stores cached basebackup archives for timelines on local disk.
+///
+/// The main purpose of this cache is to speed up the startup process of compute nodes
+/// after scaling to zero.
+/// Thus, the basebackup is stored only for the latest LSN of the timeline and with
+/// fixed set of parameters (gzip=true, full_backup=false, replica=false, prev_lsn=none).
+///
+/// The cache receives prepare requests through the `BasebackupPrepareSender` channel,
+/// generates a basebackup from the timeline in the background, and stores it on disk.
+///
+/// Basebackup requests are pretty rare. We expect ~thousands of entries in the cache
+/// and ~1 RPS for get requests.
+pub struct BasebackupCache {
+    data_dir: Utf8PathBuf,
+    config: BasebackupCacheConfig,
+    tenant_manager: Arc<TenantManager>,
+    remove_entry_sender: BasebackupRemoveEntrySender,
+
+    entries: std::sync::Mutex<HashMap<TenantTimelineId, Lsn>>,
+
+    cancel: CancellationToken,
+
+    read_hit_count: GenericCounter<AtomicU64>,
+    read_miss_count: GenericCounter<AtomicU64>,
+    read_err_count: GenericCounter<AtomicU64>,
+
+    prepare_ok_count: GenericCounter<AtomicU64>,
+    prepare_skip_count: GenericCounter<AtomicU64>,
+    prepare_err_count: GenericCounter<AtomicU64>,
+}
+
+impl BasebackupCache {
+    /// Creates a BasebackupCache and spawns the background task.
+    /// The initialization of the cache is performed in the background and does not
+    /// block the caller. The cache will return `None` for any get requests until
+    /// initialization is complete.
+    pub fn spawn(
+        runtime_handle: &tokio::runtime::Handle,
+        data_dir: Utf8PathBuf,
+        config: Option<BasebackupCacheConfig>,
+        prepare_receiver: BasebackupPrepareReceiver,
+        tenant_manager: Arc<TenantManager>,
+        cancel: CancellationToken,
+    ) -> Arc<Self> {
+        let (remove_entry_sender, remove_entry_receiver) = tokio::sync::mpsc::unbounded_channel();
+
+        let enabled = config.is_some();
+
+        let cache = Arc::new(BasebackupCache {
+            data_dir,
+            config: config.unwrap_or_default(),
+            tenant_manager,
+            remove_entry_sender,
+
+            entries: std::sync::Mutex::new(HashMap::new()),
+
+            cancel,
+
+            read_hit_count: BASEBACKUP_CACHE_READ.with_label_values(&["hit"]),
+            read_miss_count: BASEBACKUP_CACHE_READ.with_label_values(&["miss"]),
+            read_err_count: BASEBACKUP_CACHE_READ.with_label_values(&["error"]),
+
+            prepare_ok_count: BASEBACKUP_CACHE_PREPARE.with_label_values(&["ok"]),
+            prepare_skip_count: BASEBACKUP_CACHE_PREPARE.with_label_values(&["skip"]),
+            prepare_err_count: BASEBACKUP_CACHE_PREPARE.with_label_values(&["error"]),
+        });
+
+        if enabled {
+            runtime_handle.spawn(
+                cache
+                    .clone()
+                    .background(prepare_receiver, remove_entry_receiver),
+            );
+        }
+
+        cache
+    }
+
+    /// Gets a basebackup entry from the cache.
+    /// If the entry is found, opens a file with the basebackup archive and returns it.
+    /// The open file descriptor will prevent the file system from deleting the file
+    /// even if the entry is removed from the cache in the background.
+    pub async fn get(
+        &self,
+        tenant_id: TenantId,
+        timeline_id: TimelineId,
+        lsn: Lsn,
+    ) -> Option<tokio::fs::File> {
+        // Fast path. Check if the entry exists using the in-memory state.
+        let tti = TenantTimelineId::new(tenant_id, timeline_id);
+        if self.entries.lock().unwrap().get(&tti) != Some(&lsn) {
+            self.read_miss_count.inc();
+            return None;
+        }
+
+        let path = self.entry_path(tenant_id, timeline_id, lsn);
+
+        match tokio::fs::File::open(path).await {
+            Ok(file) => {
+                self.read_hit_count.inc();
+                Some(file)
+            }
+            Err(e) => {
+                if e.kind() == std::io::ErrorKind::NotFound {
+                    // We may end up here if the basebackup was concurrently removed by the cleanup task.
+                    self.read_miss_count.inc();
+                } else {
+                    self.read_err_count.inc();
+                    tracing::warn!("Unexpected error opening basebackup cache file: {:?}", e);
+                }
+                None
+            }
+        }
+    }
+
+    // Private methods.
+
+    fn entry_filename(tenant_id: TenantId, timeline_id: TimelineId, lsn: Lsn) -> String {
+        // The default format for LSN is 0/ABCDEF.
+        // The backslash is not filename friendly, so serialize it as plain hex.
+        let lsn = lsn.0;
+        format!("basebackup_{tenant_id}_{timeline_id}_{lsn:016X}.tar.gz")
+    }
+
+    fn entry_path(&self, tenant_id: TenantId, timeline_id: TimelineId, lsn: Lsn) -> Utf8PathBuf {
+        self.data_dir
+            .join(Self::entry_filename(tenant_id, timeline_id, lsn))
+    }
+
+    fn entry_tmp_path(
+        &self,
+        tenant_id: TenantId,
+        timeline_id: TimelineId,
+        lsn: Lsn,
+    ) -> Utf8PathBuf {
+        self.data_dir
+            .join("tmp")
+            .join(Self::entry_filename(tenant_id, timeline_id, lsn))
+    }
+
+    fn parse_entry_filename(filename: &str) -> Option<(TenantId, TimelineId, Lsn)> {
+        let parts: Vec<&str> = filename
+            .strip_prefix("basebackup_")?
+            .strip_suffix(".tar.gz")?
+            .split('_')
+            .collect();
+        if parts.len() != 3 {
+            return None;
+        }
+        let tenant_id = parts[0].parse::<TenantId>().ok()?;
+        let timeline_id = parts[1].parse::<TimelineId>().ok()?;
+        let lsn = Lsn(u64::from_str_radix(parts[2], 16).ok()?);
+
+        Some((tenant_id, timeline_id, lsn))
+    }
+
+    async fn cleanup(&self) -> anyhow::Result<()> {
+        // Cleanup tmp directory.
+        let tmp_dir = self.data_dir.join("tmp");
+        let mut tmp_dir = tokio::fs::read_dir(&tmp_dir).await?;
+        while let Some(dir_entry) = tmp_dir.next_entry().await? {
+            if let Err(e) = tokio::fs::remove_file(dir_entry.path()).await {
+                tracing::warn!("Failed to remove basebackup cache tmp file: {:#}", e);
+            }
+        }
+
+        // Remove outdated entries.
+        let entries_old = self.entries.lock().unwrap().clone();
+        let mut entries_new = HashMap::new();
+        for (tenant_shard_id, tenant_slot) in self.tenant_manager.list() {
+            if !tenant_shard_id.is_shard_zero() {
+                continue;
+            }
+            let TenantSlot::Attached(tenant) = tenant_slot else {
+                continue;
+            };
+            let tenant_id = tenant_shard_id.tenant_id;
+
+            for timeline in tenant.list_timelines() {
+                let tti = TenantTimelineId::new(tenant_id, timeline.timeline_id);
+                if let Some(&entry_lsn) = entries_old.get(&tti) {
+                    if timeline.get_last_record_lsn() <= entry_lsn {
+                        entries_new.insert(tti, entry_lsn);
+                    }
+                }
+            }
+        }
+
+        for (&tti, &lsn) in entries_old.iter() {
+            if !entries_new.contains_key(&tti) {
+                self.remove_entry_sender
+                    .send(self.entry_path(tti.tenant_id, tti.timeline_id, lsn))
+                    .unwrap();
+            }
+        }
+
+        BASEBACKUP_CACHE_ENTRIES.set(entries_new.len() as i64);
+        *self.entries.lock().unwrap() = entries_new;
+
+        Ok(())
+    }
+
+    async fn on_startup(&self) -> anyhow::Result<()> {
+        // Create data_dir and tmp directory if they do not exist.
+        tokio::fs::create_dir_all(&self.data_dir.join("tmp"))
+            .await
+            .map_err(|e| {
+                anyhow::anyhow!(
+                    "Failed to create basebackup cache data_dir {:?}: {:?}",
+                    self.data_dir,
+                    e
+                )
+            })?;
+
+        // Read existing entries from the data_dir and add them to in-memory state.
+        let mut entries = HashMap::new();
+        let mut dir = tokio::fs::read_dir(&self.data_dir).await?;
+        while let Some(dir_entry) = dir.next_entry().await? {
+            let filename = dir_entry.file_name();
+
+            if filename == "tmp" {
+                // Skip the tmp directory.
+                continue;
+            }
+
+            let parsed = Self::parse_entry_filename(filename.to_string_lossy().as_ref());
+            let Some((tenant_id, timeline_id, lsn)) = parsed else {
+                tracing::warn!("Invalid basebackup cache file name: {:?}", filename);
+                continue;
+            };
+
+            let tti = TenantTimelineId::new(tenant_id, timeline_id);
+
+            use std::collections::hash_map::Entry::*;
+
+            match entries.entry(tti) {
+                Occupied(mut entry) => {
+                    let entry_lsn = *entry.get();
+                    // Leave only the latest entry, remove the old one.
+                    if lsn < entry_lsn {
+                        self.remove_entry_sender.send(self.entry_path(
+                            tenant_id,
+                            timeline_id,
+                            lsn,
+                        ))?;
+                    } else if lsn > entry_lsn {
+                        self.remove_entry_sender.send(self.entry_path(
+                            tenant_id,
+                            timeline_id,
+                            entry_lsn,
+                        ))?;
+                        entry.insert(lsn);
+                    } else {
+                        // Two different filenames parsed to the same timline_id and LSN.
+                        // Should never happen.
+                        return Err(anyhow::anyhow!(
+                            "Duplicate basebackup cache entry with the same LSN: {:?}",
+                            filename
+                        ));
+                    }
+                }
+                Vacant(entry) => {
+                    entry.insert(lsn);
+                }
+            }
+        }
+
+        BASEBACKUP_CACHE_ENTRIES.set(entries.len() as i64);
+        *self.entries.lock().unwrap() = entries;
+
+        Ok(())
+    }
+
+    async fn background(
+        self: Arc<Self>,
+        mut prepare_receiver: BasebackupPrepareReceiver,
+        mut remove_entry_receiver: BasebackupRemoveEntryReceiver,
+    ) {
+        // Panic in the background is a safe fallback.
+        // It will drop receivers and the cache will be effectively disabled.
+        self.on_startup()
+            .await
+            .expect("Failed to initialize basebackup cache");
+
+        let mut cleanup_ticker = tokio::time::interval(self.config.cleanup_period);
+        cleanup_ticker.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Skip);
+
+        loop {
+            tokio::select! {
+                Some(req) = prepare_receiver.recv() => {
+                    if let Err(err) = self.prepare_basebackup(
+                        req.tenant_shard_id,
+                        req.timeline_id,
+                        req.lsn,
+                    ).await {
+                        tracing::info!("Failed to prepare basebackup: {:#}", err);
+                        self.prepare_err_count.inc();
+                        continue;
+                    }
+                }
+                Some(req) = remove_entry_receiver.recv() => {
+                    if let Err(e) = tokio::fs::remove_file(req).await {
+                        tracing::warn!("Failed to remove basebackup cache file: {:#}", e);
+                    }
+                }
+                _ = cleanup_ticker.tick() => {
+                    self.cleanup().await.unwrap_or_else(|e| {
+                        tracing::warn!("Failed to clean up basebackup cache: {:#}", e);
+                    });
+                }
+                _ = self.cancel.cancelled() => {
+                    tracing::info!("BasebackupCache background task cancelled");
+                    break;
+                }
+            }
+        }
+    }
+
+    /// Prepare a basebackup for the given timeline.
+    ///
+    /// If the basebackup already exists with a higher LSN or the timeline already
+    /// has a higher last_record_lsn, skip the preparation.
+    ///
+    /// The basebackup is prepared in a temporary directory and then moved to the final
+    /// location to make the operation atomic.
+    async fn prepare_basebackup(
+        &self,
+        tenant_shard_id: TenantShardId,
+        timeline_id: TimelineId,
+        req_lsn: Lsn,
+    ) -> anyhow::Result<()> {
+        tracing::info!(
+            tenant_id = %tenant_shard_id.tenant_id,
+            %timeline_id,
+            %req_lsn,
+            "Preparing basebackup for timeline",
+        );
+
+        let tti = TenantTimelineId::new(tenant_shard_id.tenant_id, timeline_id);
+
+        {
+            let entries = self.entries.lock().unwrap();
+            if let Some(&entry_lsn) = entries.get(&tti) {
+                if entry_lsn >= req_lsn {
+                    tracing::info!(
+                        %timeline_id,
+                        %req_lsn,
+                        %entry_lsn,
+                        "Basebackup entry already exists for timeline with higher LSN, skipping basebackup",
+                    );
+                    self.prepare_skip_count.inc();
+                    return Ok(());
+                }
+            }
+
+            if entries.len() as i64 >= self.config.max_size_entries {
+                tracing::info!(
+                    %timeline_id,
+                    %req_lsn,
+                    "Basebackup cache is full, skipping basebackup",
+                );
+                self.prepare_skip_count.inc();
+                return Ok(());
+            }
+        }
+
+        let tenant = self
+            .tenant_manager
+            .get_attached_tenant_shard(tenant_shard_id)?;
+
+        let tenant_state = tenant.current_state();
+        if tenant_state != TenantState::Active {
+            anyhow::bail!(
+                "Tenant {} is not active, current state: {:?}",
+                tenant_shard_id.tenant_id,
+                tenant_state
+            )
+        }
+
+        let timeline = tenant.get_timeline(timeline_id, true)?;
+
+        let last_record_lsn = timeline.get_last_record_lsn();
+        if last_record_lsn > req_lsn {
+            tracing::info!(
+                %timeline_id,
+                %req_lsn,
+                %last_record_lsn,
+                "Timeline has a higher LSN than the requested one, skipping basebackup",
+            );
+            self.prepare_skip_count.inc();
+            return Ok(());
+        }
+
+        let entry_tmp_path = self.entry_tmp_path(tenant_shard_id.tenant_id, timeline_id, req_lsn);
+
+        let res = self
+            .prepare_basebackup_tmp(&entry_tmp_path, &timeline, req_lsn)
+            .await;
+
+        if let Err(err) = res {
+            tracing::info!("Failed to prepare basebackup tmp file: {:#}", err);
+            // Try to clean up tmp file. If we fail, the background clean up task will take care of it.
+            match tokio::fs::remove_file(&entry_tmp_path).await {
+                Ok(_) => {}
+                Err(e) if e.kind() == std::io::ErrorKind::NotFound => {}
+                Err(e) => {
+                    tracing::info!("Failed to remove basebackup tmp file: {:?}", e);
+                }
+            }
+            return Err(err);
+        }
+
+        // Move the tmp file to the final location atomically.
+        let entry_path = self.entry_path(tenant_shard_id.tenant_id, timeline_id, req_lsn);
+        tokio::fs::rename(&entry_tmp_path, &entry_path).await?;
+
+        let mut entries = self.entries.lock().unwrap();
+        if let Some(old_lsn) = entries.insert(tti, req_lsn) {
+            // Remove the old entry if it exists.
+            self.remove_entry_sender
+                .send(self.entry_path(tenant_shard_id.tenant_id, timeline_id, old_lsn))
+                .unwrap();
+        }
+        BASEBACKUP_CACHE_ENTRIES.set(entries.len() as i64);
+
+        self.prepare_ok_count.inc();
+        Ok(())
+    }
+
+    /// Prepares a basebackup in a temporary file.
+    async fn prepare_basebackup_tmp(
+        &self,
+        emptry_tmp_path: &Utf8Path,
+        timeline: &Arc<Timeline>,
+        req_lsn: Lsn,
+    ) -> anyhow::Result<()> {
+        let ctx = RequestContext::new(TaskKind::BasebackupCache, DownloadBehavior::Download);
+        let ctx = ctx.with_scope_timeline(timeline);
+
+        let file = tokio::fs::File::create(emptry_tmp_path).await?;
+        let mut writer = BufWriter::new(file);
+
+        let mut encoder = GzipEncoder::with_quality(
+            &mut writer,
+            // Level::Best because compression is not on the hot path of basebackup requests.
+            // The decompression is almost not affected by the compression level.
+            async_compression::Level::Best,
+        );
+
+        // We may receive a request before the WAL record is applied to the timeline.
+        // Wait for the requested LSN to be applied.
+        timeline
+            .wait_lsn(
+                req_lsn,
+                crate::tenant::timeline::WaitLsnWaiter::BaseBackupCache,
+                crate::tenant::timeline::WaitLsnTimeout::Default,
+                &ctx,
+            )
+            .await?;
+
+        send_basebackup_tarball(
+            &mut encoder,
+            timeline,
+            Some(req_lsn),
+            None,
+            false,
+            false,
+            &ctx,
+        )
+        .await?;
+
+        encoder.shutdown().await?;
+        writer.flush().await?;
+        writer.into_inner().sync_all().await?;
+
+        Ok(())
+    }
+}

pageserver/src/bin/pageserver.rs

@@ -16,6 +16,7 @@ use http_utils::tls_certs::ReloadingCertificateResolver;
 use metrics::launch_timestamp::{LaunchTimestamp, set_launch_timestamp_metric};
 use metrics::set_build_info_metric;
 use nix::sys::socket::{setsockopt, sockopt};
+use pageserver::basebackup_cache::BasebackupCache;
 use pageserver::config::{PageServerConf, PageserverIdentity, ignored_fields};
 use pageserver::controller_upcall_client::StorageControllerUpcallClient;
 use pageserver::deletion_queue::DeletionQueue;
@@ -541,6 +542,8 @@ fn start_pageserver(
         pageserver::l0_flush::L0FlushGlobalState::new(conf.l0_flush.clone());
 
     // Scan the local 'tenants/' directory and start loading the tenants
+    let (basebackup_prepare_sender, basebackup_prepare_receiver) =
+        tokio::sync::mpsc::unbounded_channel();
     let deletion_queue_client = deletion_queue.new_client();
     let background_purges = mgr::BackgroundPurges::default();
     let tenant_manager = BACKGROUND_RUNTIME.block_on(mgr::init_tenant_mgr(
@@ -551,12 +554,22 @@ fn start_pageserver(
             remote_storage: remote_storage.clone(),
             deletion_queue_client,
             l0_flush_global_state,
+            basebackup_prepare_sender,
         },
         order,
         shutdown_pageserver.clone(),
     ))?;
     let tenant_manager = Arc::new(tenant_manager);
 
+    let basebackup_cache = BasebackupCache::spawn(
+        BACKGROUND_RUNTIME.handle(),
+        conf.basebackup_cache_dir(),
+        conf.basebackup_cache_config.clone(),
+        basebackup_prepare_receiver,
+        Arc::clone(&tenant_manager),
+        shutdown_pageserver.child_token(),
+    );
+
     BACKGROUND_RUNTIME.spawn({
         let shutdown_pageserver = shutdown_pageserver.clone();
         let drive_init = async move {
@@ -763,6 +776,7 @@ fn start_pageserver(
         } else {
             None
         },
+        basebackup_cache,
     );
 
     // All started up! Now just sit and wait for shutdown signal.

pageserver/src/config.rs

@@ -232,6 +232,8 @@ pub struct PageServerConf {
     pub dev_mode: bool,
 
     pub timeline_import_config: pageserver_api::config::TimelineImportConfig,
+
+    pub basebackup_cache_config: Option<pageserver_api::config::BasebackupCacheConfig>,
 }
 
 /// Token for authentication to safekeepers
@@ -261,6 +263,10 @@ impl PageServerConf {
         self.workdir.join("metadata.json")
     }
 
+    pub fn basebackup_cache_dir(&self) -> Utf8PathBuf {
+        self.workdir.join("basebackup_cache")
+    }
+
     pub fn deletion_list_path(&self, sequence: u64) -> Utf8PathBuf {
         // Encode a version in the filename, so that if we ever switch away from JSON we can
         // increment this.
@@ -407,6 +413,7 @@ impl PageServerConf {
             enable_tls_page_service_api,
             dev_mode,
             timeline_import_config,
+            basebackup_cache_config,
         } = config_toml;
 
         let mut conf = PageServerConf {
@@ -461,6 +468,7 @@ impl PageServerConf {
             enable_tls_page_service_api,
             dev_mode,
             timeline_import_config,
+            basebackup_cache_config,
 
             // ------------------------------------------------------------
             // fields that require additional validation or custom handling

pageserver/src/lib.rs

@@ -3,6 +3,7 @@
 
 mod auth;
 pub mod basebackup;
+pub mod basebackup_cache;
 pub mod config;
 pub mod consumption_metrics;
 pub mod context;

pageserver/src/metrics.rs

@@ -4359,6 +4359,42 @@ pub(crate) fn set_tokio_runtime_setup(setup: &str, num_threads: NonZeroUsize) {
         .set(u64::try_from(num_threads.get()).unwrap());
 }
 
+pub(crate) static BASEBACKUP_CACHE_READ: Lazy<IntCounterVec> = Lazy::new(|| {
+    register_int_counter_vec!(
+        "pageserver_basebackup_cache_read_total",
+        "Number of read accesses to the basebackup cache grouped by hit/miss/error",
+        &["result"]
+    )
+    .expect("failed to define a metric")
+});
+
+pub(crate) static BASEBACKUP_CACHE_PREPARE: Lazy<IntCounterVec> = Lazy::new(|| {
+    register_int_counter_vec!(
+        "pageserver_basebackup_cache_prepare_total",
+        "Number of prepare requests processed by the basebackup cache grouped by ok/skip/error",
+        &["result"]
+    )
+    .expect("failed to define a metric")
+});
+
+pub(crate) static BASEBACKUP_CACHE_ENTRIES: Lazy<IntGauge> = Lazy::new(|| {
+    register_int_gauge!(
+        "pageserver_basebackup_cache_entries_total",
+        "Number of entries in the basebackup cache"
+    )
+    .expect("failed to define a metric")
+});
+
+// FIXME: Support basebackup cache size metrics.
+#[allow(dead_code)]
+pub(crate) static BASEBACKUP_CACHE_SIZE: Lazy<IntGauge> = Lazy::new(|| {
+    register_int_gauge!(
+        "pageserver_basebackup_cache_size_bytes",
+        "Total size of all basebackup cache entries on disk in bytes"
+    )
+    .expect("failed to define a metric")
+});
+
 static PAGESERVER_CONFIG_IGNORED_ITEMS: Lazy<UIntGaugeVec> = Lazy::new(|| {
     register_uint_gauge_vec!(
         "pageserver_config_ignored_items",

pageserver/src/page_service.rs

@@ -9,7 +9,6 @@ use std::sync::Arc;
 use std::time::{Duration, Instant, SystemTime};
 use std::{io, str};
 
-use crate::PERF_TRACE_TARGET;
 use anyhow::{Context, bail};
 use async_compression::tokio::write::GzipEncoder;
 use bytes::Buf;
@@ -52,8 +51,10 @@ use utils::simple_rcu::RcuReadGuard;
 use utils::sync::gate::{Gate, GateGuard};
 use utils::sync::spsc_fold;
 
+use crate::PERF_TRACE_TARGET;
 use crate::auth::check_permission;
 use crate::basebackup::BasebackupError;
+use crate::basebackup_cache::BasebackupCache;
 use crate::config::PageServerConf;
 use crate::context::{
     DownloadBehavior, PerfInstrumentFutureExt, RequestContext, RequestContextBuilder,
@@ -107,6 +108,7 @@ pub fn spawn(
     perf_trace_dispatch: Option<Dispatch>,
     tcp_listener: tokio::net::TcpListener,
     tls_config: Option<Arc<rustls::ServerConfig>>,
+    basebackup_cache: Arc<BasebackupCache>,
 ) -> Listener {
     let cancel = CancellationToken::new();
     let libpq_ctx = RequestContext::todo_child(
@@ -128,6 +130,7 @@ pub fn spawn(
             conf.pg_auth_type,
             tls_config,
             conf.page_service_pipelining.clone(),
+            basebackup_cache,
             libpq_ctx,
             cancel.clone(),
         )
@@ -186,6 +189,7 @@ pub async fn libpq_listener_main(
     auth_type: AuthType,
     tls_config: Option<Arc<rustls::ServerConfig>>,
     pipelining_config: PageServicePipeliningConfig,
+    basebackup_cache: Arc<BasebackupCache>,
     listener_ctx: RequestContext,
     listener_cancel: CancellationToken,
 ) -> Connections {
@@ -229,6 +233,7 @@ pub async fn libpq_listener_main(
                     auth_type,
                     tls_config.clone(),
                     pipelining_config.clone(),
+                    Arc::clone(&basebackup_cache),
                     connection_ctx,
                     connections_cancel.child_token(),
                     gate_guard,
@@ -271,6 +276,7 @@ async fn page_service_conn_main(
     auth_type: AuthType,
     tls_config: Option<Arc<rustls::ServerConfig>>,
     pipelining_config: PageServicePipeliningConfig,
+    basebackup_cache: Arc<BasebackupCache>,
     connection_ctx: RequestContext,
     cancel: CancellationToken,
     gate_guard: GateGuard,
@@ -336,6 +342,7 @@ async fn page_service_conn_main(
         pipelining_config,
         conf.get_vectored_concurrent_io,
         perf_span_fields,
+        basebackup_cache,
         connection_ctx,
         cancel.clone(),
         gate_guard,
@@ -390,6 +397,8 @@ struct PageServerHandler {
     pipelining_config: PageServicePipeliningConfig,
     get_vectored_concurrent_io: GetVectoredConcurrentIo,
 
+    basebackup_cache: Arc<BasebackupCache>,
+
     gate_guard: GateGuard,
 }
 
@@ -849,6 +858,7 @@ impl PageServerHandler {
         pipelining_config: PageServicePipeliningConfig,
         get_vectored_concurrent_io: GetVectoredConcurrentIo,
         perf_span_fields: ConnectionPerfSpanFields,
+        basebackup_cache: Arc<BasebackupCache>,
         connection_ctx: RequestContext,
         cancel: CancellationToken,
         gate_guard: GateGuard,
@@ -862,6 +872,7 @@ impl PageServerHandler {
             cancel,
             pipelining_config,
             get_vectored_concurrent_io,
+            basebackup_cache,
             gate_guard,
         }
     }
@@ -2493,6 +2504,8 @@ impl PageServerHandler {
             .map_err(QueryError::Disconnected)?;
         self.flush_cancellable(pgb, &self.cancel).await?;
 
+        let mut from_cache = false;
+
         // Send a tarball of the latest layer on the timeline. Compress if not
         // fullbackup. TODO Compress in that case too (tests need to be updated)
         if full_backup {
@@ -2510,7 +2523,33 @@ impl PageServerHandler {
             .map_err(map_basebackup_error)?;
         } else {
             let mut writer = BufWriter::new(pgb.copyout_writer());
-            if gzip {
+
+            let cached = {
+                // Basebackup is cached only for this combination of parameters.
+                if timeline.is_basebackup_cache_enabled()
+                    && gzip
+                    && lsn.is_some()
+                    && prev_lsn.is_none()
+                {
+                    self.basebackup_cache
+                        .get(tenant_id, timeline_id, lsn.unwrap())
+                        .await
+                } else {
+                    None
+                }
+            };
+
+            if let Some(mut cached) = cached {
+                from_cache = true;
+                tokio::io::copy(&mut cached, &mut writer)
+                    .await
+                    .map_err(|e| {
+                        map_basebackup_error(BasebackupError::Client(
+                            e,
+                            "handle_basebackup_request,cached,copy",
+                        ))
+                    })?;
+            } else if gzip {
                 let mut encoder = GzipEncoder::with_quality(
                     &mut writer,
                     // NOTE using fast compression because it's on the critical path
@@ -2569,6 +2608,7 @@ impl PageServerHandler {
         info!(
             lsn_await_millis = lsn_awaited_after.as_millis(),
             basebackup_millis = basebackup_after.as_millis(),
+            %from_cache,
             "basebackup complete"
         );
 

pageserver/src/task_mgr.rs

@@ -380,6 +380,10 @@ pub enum TaskKind {
     DetachAncestor,
 
     ImportPgdata,
+
+    /// Background task of [`crate::basebackup_cache::BasebackupCache`].
+    /// Prepares basebackups and clears outdated entries.
+    BasebackupCache,
 }
 
 #[derive(Default)]

pageserver/src/tenant.rs

@@ -78,6 +78,7 @@ use self::timeline::uninit::{TimelineCreateGuard, TimelineExclusionError, Uninit
 use self::timeline::{
     EvictionTaskTenantState, GcCutoffs, TimelineDeleteProgress, TimelineResources, WaitLsnError,
 };
+use crate::basebackup_cache::BasebackupPrepareSender;
 use crate::config::PageServerConf;
 use crate::context;
 use crate::context::RequestContextBuilder;
@@ -157,6 +158,7 @@ pub struct TenantSharedResources {
     pub remote_storage: GenericRemoteStorage,
     pub deletion_queue_client: DeletionQueueClient,
     pub l0_flush_global_state: L0FlushGlobalState,
+    pub basebackup_prepare_sender: BasebackupPrepareSender,
 }
 
 /// A [`TenantShard`] is really an _attached_ tenant.  The configuration
@@ -317,12 +319,15 @@ pub struct TenantShard {
     gc_cs: tokio::sync::Mutex<()>,
     walredo_mgr: Option<Arc<WalRedoManager>>,
 
-    // provides access to timeline data sitting in the remote storage
+    /// Provides access to timeline data sitting in the remote storage.
     pub(crate) remote_storage: GenericRemoteStorage,
 
-    // Access to global deletion queue for when this tenant wants to schedule a deletion
+    /// Access to global deletion queue for when this tenant wants to schedule a deletion.
     deletion_queue_client: DeletionQueueClient,
 
+    /// A channel to send async requests to prepare a basebackup for the basebackup cache.
+    basebackup_prepare_sender: BasebackupPrepareSender,
+
     /// Cached logical sizes updated updated on each [`TenantShard::gather_size_inputs`].
     cached_logical_sizes: tokio::sync::Mutex<HashMap<(TimelineId, Lsn), u64>>,
     cached_synthetic_tenant_size: Arc<AtomicU64>,
@@ -1286,6 +1291,7 @@ impl TenantShard {
             remote_storage,
             deletion_queue_client,
             l0_flush_global_state,
+            basebackup_prepare_sender,
         } = resources;
 
         let attach_mode = attached_conf.location.attach_mode;
@@ -1301,6 +1307,7 @@ impl TenantShard {
             remote_storage.clone(),
             deletion_queue_client,
             l0_flush_global_state,
+            basebackup_prepare_sender,
         ));
 
         // The attach task will carry a GateGuard, so that shutdown() reliably waits for it to drop out if
@@ -4239,6 +4246,7 @@ impl TenantShard {
         remote_storage: GenericRemoteStorage,
         deletion_queue_client: DeletionQueueClient,
         l0_flush_global_state: L0FlushGlobalState,
+        basebackup_prepare_sender: BasebackupPrepareSender,
     ) -> TenantShard {
         assert!(!attached_conf.location.generation.is_none());
 
@@ -4342,6 +4350,7 @@ impl TenantShard {
             ongoing_timeline_detach: std::sync::Mutex::default(),
             gc_block: Default::default(),
             l0_flush_global_state,
+            basebackup_prepare_sender,
         }
     }
 
@@ -5261,6 +5270,7 @@ impl TenantShard {
             pagestream_throttle_metrics: self.pagestream_throttle_metrics.clone(),
             l0_compaction_trigger: self.l0_compaction_trigger.clone(),
             l0_flush_global_state: self.l0_flush_global_state.clone(),
+            basebackup_prepare_sender: self.basebackup_prepare_sender.clone(),
         }
     }
 
@@ -5843,6 +5853,8 @@ pub(crate) mod harness {
         ) -> anyhow::Result<Arc<TenantShard>> {
             let walredo_mgr = Arc::new(WalRedoManager::from(TestRedoManager));
 
+            let (basebackup_requst_sender, _) = tokio::sync::mpsc::unbounded_channel();
+
             let tenant = Arc::new(TenantShard::new(
                 TenantState::Attaching,
                 self.conf,
@@ -5860,6 +5872,7 @@ pub(crate) mod harness {
                 self.deletion_queue.new_client(),
                 // TODO: ideally we should run all unit tests with both configs
                 L0FlushGlobalState::new(L0FlushConfig::default()),
+                basebackup_requst_sender,
             ));
 
             let preload = tenant

pageserver/src/tenant/timeline.rs

@@ -24,8 +24,6 @@ use std::sync::atomic::{AtomicBool, AtomicU64, Ordering as AtomicOrdering};
 use std::sync::{Arc, Mutex, OnceLock, RwLock, Weak};
 use std::time::{Duration, Instant, SystemTime};
 
-use crate::PERF_TRACE_TARGET;
-use crate::walredo::RedoAttemptType;
 use anyhow::{Context, Result, anyhow, bail, ensure};
 use arc_swap::{ArcSwap, ArcSwapOption};
 use bytes::Bytes;
@@ -94,10 +92,12 @@ use super::storage_layer::{LayerFringe, LayerVisibilityHint, ReadableLayer};
 use super::tasks::log_compaction_error;
 use super::upload_queue::NotInitialized;
 use super::{
-    AttachedTenantConf, GcError, HeatMapTimeline, MaybeOffloaded,
+    AttachedTenantConf, BasebackupPrepareSender, GcError, HeatMapTimeline, MaybeOffloaded,
     debug_assert_current_span_has_tenant_and_timeline_id,
 };
+use crate::PERF_TRACE_TARGET;
 use crate::aux_file::AuxFileSizeEstimator;
+use crate::basebackup_cache::BasebackupPrepareRequest;
 use crate::config::PageServerConf;
 use crate::context::{
     DownloadBehavior, PerfInstrumentFutureExt, RequestContext, RequestContextBuilder,
@@ -131,6 +131,7 @@ use crate::tenant::tasks::BackgroundLoopKind;
 use crate::tenant::timeline::logical_size::CurrentLogicalSize;
 use crate::virtual_file::{MaybeFatalIo, VirtualFile};
 use crate::walingest::WalLagCooldown;
+use crate::walredo::RedoAttemptType;
 use crate::{ZERO_PAGE, task_mgr, walredo};
 
 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
@@ -196,6 +197,7 @@ pub struct TimelineResources {
     pub pagestream_throttle_metrics: Arc<crate::metrics::tenant_throttling::Pagestream>,
     pub l0_compaction_trigger: Arc<Notify>,
     pub l0_flush_global_state: l0_flush::L0FlushGlobalState,
+    pub basebackup_prepare_sender: BasebackupPrepareSender,
 }
 
 pub struct Timeline {
@@ -439,6 +441,9 @@ pub struct Timeline {
     pub(crate) rel_size_v2_status: ArcSwapOption<RelSizeMigration>,
 
     wait_lsn_log_slow: tokio::sync::Semaphore,
+
+    /// A channel to send async requests to prepare a basebackup for the basebackup cache.
+    basebackup_prepare_sender: BasebackupPrepareSender,
 }
 
 pub(crate) enum PreviousHeatmap {
@@ -1028,6 +1033,7 @@ pub(crate) enum WaitLsnWaiter<'a> {
     Tenant,
     PageService,
     HttpEndpoint,
+    BaseBackupCache,
 }
 
 /// Argument to [`Timeline::shutdown`].
@@ -1554,7 +1560,8 @@ impl Timeline {
                         }
                         WaitLsnWaiter::Tenant
                         | WaitLsnWaiter::PageService
-                        | WaitLsnWaiter::HttpEndpoint => unreachable!(
+                        | WaitLsnWaiter::HttpEndpoint
+                        | WaitLsnWaiter::BaseBackupCache => unreachable!(
                             "tenant or page_service context are not expected to have task kind {:?}",
                             ctx.task_kind()
                         ),
@@ -2459,6 +2466,41 @@ impl Timeline {
             false
         }
     }
+
+    pub(crate) fn is_basebackup_cache_enabled(&self) -> bool {
+        let tenant_conf = self.tenant_conf.load();
+        tenant_conf
+            .tenant_conf
+            .basebackup_cache_enabled
+            .unwrap_or(self.conf.default_tenant_conf.basebackup_cache_enabled)
+    }
+
+    /// Prepare basebackup for the given LSN and store it in the basebackup cache.
+    /// The method is asynchronous and returns immediately.
+    /// The actual basebackup preparation is performed in the background
+    /// by the basebackup cache on a best-effort basis.
+    pub(crate) fn prepare_basebackup(&self, lsn: Lsn) {
+        if !self.is_basebackup_cache_enabled() {
+            return;
+        }
+        if !self.tenant_shard_id.is_shard_zero() {
+            // In theory we should never get here, but just in case check it.
+            // Preparing basebackup doesn't make sense for shards other than shard zero.
+            return;
+        }
+
+        let res = self
+            .basebackup_prepare_sender
+            .send(BasebackupPrepareRequest {
+                tenant_shard_id: self.tenant_shard_id,
+                timeline_id: self.timeline_id,
+                lsn,
+            });
+        if let Err(e) = res {
+            // May happen during shutdown, it's not critical.
+            info!("Failed to send shutdown checkpoint: {e:#}");
+        }
+    }
 }
 
 /// Number of times we will compute partition within a checkpoint distance.
@@ -3028,6 +3070,8 @@ impl Timeline {
                 rel_size_v2_status: ArcSwapOption::from_pointee(rel_size_v2_status),
 
                 wait_lsn_log_slow: tokio::sync::Semaphore::new(1),
+
+                basebackup_prepare_sender: resources.basebackup_prepare_sender,
             };
 
             result.repartition_threshold =

pageserver/src/walingest.rs

@@ -1316,6 +1316,10 @@ impl WalIngest {
             }
         });
 
+        if info == pg_constants::XLOG_CHECKPOINT_SHUTDOWN {
+            modification.tline.prepare_basebackup(lsn);
+        }
+
         Ok(())
     }
 

test_runner/regress/test_basebackup.py

@@ -0,0 +1,77 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from fixtures.utils import wait_until
+
+if TYPE_CHECKING:
+    from fixtures.neon_fixtures import NeonEnvBuilder
+
+
+def test_basebackup_cache(neon_env_builder: NeonEnvBuilder):
+    """
+    Simple test for basebackup cache.
+    1. Check that we always hit the cache after compute restart.
+    2. Check that we eventually delete old basebackup files, but not the latest one.
+    3. Check that we delete basebackup file for timeline with active compute.
+    """
+
+    neon_env_builder.pageserver_config_override = """
+        tenant_config = { basebackup_cache_enabled = true }
+        basebackup_cache_config = { cleanup_period = '1s' }
+    """
+
+    env = neon_env_builder.init_start()
+    ep = env.endpoints.create("main")
+    ps = env.pageserver
+    ps_http = ps.http_client()
+
+    # 1. Check that we always hit the cache after compute restart.
+    for i in range(3):
+        ep.start()
+        ep.stop()
+
+        def check_metrics(i=i):
+            metrics = ps_http.get_metrics()
+            # Never miss.
+            # The first time compute_ctl sends `get_basebackup` with lsn=None, we do not cache such requests.
+            # All other requests should be a hit
+            assert (
+                metrics.query_one(
+                    "pageserver_basebackup_cache_read_total", {"result": "miss"}
+                ).value
+                == 0
+            )
+            # All but the first requests are hits.
+            assert (
+                metrics.query_one("pageserver_basebackup_cache_read_total", {"result": "hit"}).value
+                == i
+            )
+            # Every compute shut down should trigger a prepare reuest.
+            assert (
+                metrics.query_one(
+                    "pageserver_basebackup_cache_prepare_total", {"result": "ok"}
+                ).value
+                == i + 1
+            )
+
+        wait_until(check_metrics)
+
+    # 2. Check that we eventually delete old basebackup files, but not the latest one.
+    def check_bb_file_count():
+        bb_files = list(ps.workdir.joinpath("basebackup_cache").iterdir())
+        # tmp dir + 1 basebackup file.
+        assert len(bb_files) == 2
+
+    wait_until(check_bb_file_count)
+
+    # 3. Check that we delete basebackup file for timeline with active compute.
+    ep.start()
+    ep.safe_psql("create table t1 as select generate_series(1, 10) as n")
+
+    def check_bb_dir_empty():
+        bb_files = list(ps.workdir.joinpath("basebackup_cache").iterdir())
+        # only tmp dir.
+        assert len(bb_files) == 1
+
+    wait_until(check_bb_dir_empty)