LCOV - code coverage report
Current view: top level - pageserver/src/tenant/storage_layer - layer.rs (source / functions) Coverage Total Hit
Test: f2bfe5dc5ab550768e936d6bc7b94d9b2e2d4cc9.info Lines: 78.5 % 1318 1035
Test Date: 2025-01-27 20:39:28 Functions: 79.0 % 143 113

            Line data    Source code
       1              : use anyhow::Context;
       2              : use camino::{Utf8Path, Utf8PathBuf};
       3              : use pageserver_api::keyspace::KeySpace;
       4              : use pageserver_api::models::HistoricLayerInfo;
       5              : use pageserver_api::shard::{ShardIdentity, ShardIndex, TenantShardId};
       6              : use std::ops::Range;
       7              : use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
       8              : use std::sync::{Arc, Weak};
       9              : use std::time::{Duration, SystemTime};
      10              : use tracing::Instrument;
      11              : use utils::id::TimelineId;
      12              : use utils::lsn::Lsn;
      13              : use utils::sync::{gate, heavier_once_cell};
      14              : 
      15              : use crate::config::PageServerConf;
      16              : use crate::context::{DownloadBehavior, RequestContext, RequestContextBuilder};
      17              : use crate::span::debug_assert_current_span_has_tenant_and_timeline_id;
      18              : use crate::task_mgr::TaskKind;
      19              : use crate::tenant::timeline::{CompactionError, GetVectoredError};
      20              : use crate::tenant::{remote_timeline_client::LayerFileMetadata, Timeline};
      21              : 
      22              : use super::delta_layer::{self};
      23              : use super::image_layer::{self};
      24              : use super::{
      25              :     AsLayerDesc, ImageLayerWriter, LayerAccessStats, LayerAccessStatsReset, LayerName,
      26              :     LayerVisibilityHint, PersistentLayerDesc, ValuesReconstructState,
      27              : };
      28              : 
      29              : use utils::generation::Generation;
      30              : 
      31              : #[cfg(test)]
      32              : mod tests;
      33              : 
      34              : #[cfg(test)]
      35              : mod failpoints;
      36              : 
      37              : pub const S3_UPLOAD_LIMIT: u64 = 4_500_000_000;
      38              : 
      39              : /// A Layer contains all data in a "rectangle" consisting of a range of keys and
      40              : /// range of LSNs.
      41              : ///
      42              : /// There are two kinds of layers, in-memory and on-disk layers. In-memory
      43              : /// layers are used to ingest incoming WAL, and provide fast access to the
      44              : /// recent page versions. On-disk layers are stored as files on disk, and are
      45              : /// immutable. This type represents the on-disk kind while in-memory kind are represented by
      46              : /// [`InMemoryLayer`].
      47              : ///
      48              : /// Furthermore, there are two kinds of on-disk layers: delta and image layers.
      49              : /// A delta layer contains all modifications within a range of LSNs and keys.
      50              : /// An image layer is a snapshot of all the data in a key-range, at a single
      51              : /// LSN.
      52              : ///
      53              : /// This type models the on-disk layers, which can be evicted and on-demand downloaded. As a
      54              : /// general goal, read accesses should always win eviction and eviction should not wait for
      55              : /// download.
      56              : ///
      57              : /// ### State transitions
      58              : ///
      59              : /// The internal state of `Layer` is composed of most importantly the on-filesystem state and the
      60              : /// [`ResidentOrWantedEvicted`] enum. On-filesystem state can be either present (fully downloaded,
      61              : /// right size) or deleted.
      62              : ///
      63              : /// Reads will always win requests to evict until `wait_for_turn_and_evict` has acquired the
      64              : /// `heavier_once_cell::InitPermit` and has started to `evict_blocking`. Before the
      65              : /// `heavier_once_cell::InitPermit` has been acquired, any read request
      66              : /// (`get_or_maybe_download`) can "re-initialize" using the existing downloaded file and thus
      67              : /// cancelling the eviction.
      68              : ///
      69              : /// ```text
      70              : ///  +-----------------+   get_or_maybe_download    +--------------------------------+
      71              : ///  | not initialized |--------------------------->| Resident(Arc<DownloadedLayer>) |
      72              : ///  |     ENOENT      |                         /->|                                |
      73              : ///  +-----------------+                         |  +--------------------------------+
      74              : ///                  ^                           |                         |       ^
      75              : ///                  |    get_or_maybe_download  |                         |       | get_or_maybe_download, either:
      76              : ///   evict_blocking | /-------------------------/                         |       | - upgrade weak to strong
      77              : ///                  | |                                                   |       | - re-initialize without download
      78              : ///                  | |                                    evict_and_wait |       |
      79              : ///  +-----------------+                                                   v       |
      80              : ///  | not initialized |  on_downloaded_layer_drop  +--------------------------------------+
      81              : ///  | file is present |<---------------------------| WantedEvicted(Weak<DownloadedLayer>) |
      82              : ///  +-----------------+                            +--------------------------------------+
      83              : /// ```
      84              : ///
      85              : /// ### Unsupported
      86              : ///
      87              : /// - Evicting by the operator deleting files from the filesystem
      88              : ///
      89              : /// [`InMemoryLayer`]: super::inmemory_layer::InMemoryLayer
      90              : #[derive(Clone)]
      91              : pub(crate) struct Layer(Arc<LayerInner>);
      92              : 
      93              : impl std::fmt::Display for Layer {
      94         4268 :     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
      95         4268 :         write!(
      96         4268 :             f,
      97         4268 :             "{}{}",
      98         4268 :             self.layer_desc().short_id(),
      99         4268 :             self.0.generation.get_suffix()
     100         4268 :         )
     101         4268 :     }
     102              : }
     103              : 
     104              : impl std::fmt::Debug for Layer {
     105            8 :     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
     106            8 :         write!(f, "{}", self)
     107            8 :     }
     108              : }
     109              : 
     110              : impl AsLayerDesc for Layer {
     111      3363509 :     fn layer_desc(&self) -> &PersistentLayerDesc {
     112      3363509 :         self.0.layer_desc()
     113      3363509 :     }
     114              : }
     115              : 
     116              : impl PartialEq for Layer {
     117            7 :     fn eq(&self, other: &Self) -> bool {
     118            7 :         Arc::as_ptr(&self.0) == Arc::as_ptr(&other.0)
     119            7 :     }
     120              : }
     121              : 
     122         3800 : pub(crate) fn local_layer_path(
     123         3800 :     conf: &PageServerConf,
     124         3800 :     tenant_shard_id: &TenantShardId,
     125         3800 :     timeline_id: &TimelineId,
     126         3800 :     layer_file_name: &LayerName,
     127         3800 :     generation: &Generation,
     128         3800 : ) -> Utf8PathBuf {
     129         3800 :     let timeline_path = conf.timeline_path(tenant_shard_id, timeline_id);
     130         3800 : 
     131         3800 :     if generation.is_none() {
     132              :         // Without a generation, we may only use legacy path style
     133            0 :         timeline_path.join(layer_file_name.to_string())
     134              :     } else {
     135         3800 :         timeline_path.join(format!("{}-v1{}", layer_file_name, generation.get_suffix()))
     136              :     }
     137         3800 : }
     138              : 
     139              : impl Layer {
     140              :     /// Creates a layer value for a file we know to not be resident.
     141            0 :     pub(crate) fn for_evicted(
     142            0 :         conf: &'static PageServerConf,
     143            0 :         timeline: &Arc<Timeline>,
     144            0 :         file_name: LayerName,
     145            0 :         metadata: LayerFileMetadata,
     146            0 :     ) -> Self {
     147            0 :         let local_path = local_layer_path(
     148            0 :             conf,
     149            0 :             &timeline.tenant_shard_id,
     150            0 :             &timeline.timeline_id,
     151            0 :             &file_name,
     152            0 :             &metadata.generation,
     153            0 :         );
     154            0 : 
     155            0 :         let desc = PersistentLayerDesc::from_filename(
     156            0 :             timeline.tenant_shard_id,
     157            0 :             timeline.timeline_id,
     158            0 :             file_name,
     159            0 :             metadata.file_size,
     160            0 :         );
     161            0 : 
     162            0 :         let owner = Layer(Arc::new(LayerInner::new(
     163            0 :             conf,
     164            0 :             timeline,
     165            0 :             local_path,
     166            0 :             desc,
     167            0 :             None,
     168            0 :             metadata.generation,
     169            0 :             metadata.shard,
     170            0 :         )));
     171            0 : 
     172            0 :         debug_assert!(owner.0.needs_download_blocking().unwrap().is_some());
     173              : 
     174            0 :         owner
     175            0 :     }
     176              : 
     177              :     /// Creates a Layer value for a file we know to be resident in timeline directory.
     178          244 :     pub(crate) fn for_resident(
     179          244 :         conf: &'static PageServerConf,
     180          244 :         timeline: &Arc<Timeline>,
     181          244 :         local_path: Utf8PathBuf,
     182          244 :         file_name: LayerName,
     183          244 :         metadata: LayerFileMetadata,
     184          244 :     ) -> ResidentLayer {
     185          244 :         let desc = PersistentLayerDesc::from_filename(
     186          244 :             timeline.tenant_shard_id,
     187          244 :             timeline.timeline_id,
     188          244 :             file_name,
     189          244 :             metadata.file_size,
     190          244 :         );
     191          244 : 
     192          244 :         let mut resident = None;
     193          244 : 
     194          244 :         let owner = Layer(Arc::new_cyclic(|owner| {
     195          244 :             let inner = Arc::new(DownloadedLayer {
     196          244 :                 owner: owner.clone(),
     197          244 :                 kind: tokio::sync::OnceCell::default(),
     198          244 :                 version: 0,
     199          244 :             });
     200          244 :             resident = Some(inner.clone());
     201          244 : 
     202          244 :             LayerInner::new(
     203          244 :                 conf,
     204          244 :                 timeline,
     205          244 :                 local_path,
     206          244 :                 desc,
     207          244 :                 Some(inner),
     208          244 :                 metadata.generation,
     209          244 :                 metadata.shard,
     210          244 :             )
     211          244 :         }));
     212          244 : 
     213          244 :         let downloaded = resident.expect("just initialized");
     214          244 : 
     215          244 :         debug_assert!(owner.0.needs_download_blocking().unwrap().is_none());
     216              : 
     217          244 :         timeline
     218          244 :             .metrics
     219          244 :             .resident_physical_size_add(metadata.file_size);
     220          244 : 
     221          244 :         ResidentLayer { downloaded, owner }
     222          244 :     }
     223              : 
     224              :     /// Creates a Layer value for freshly written out new layer file by renaming it from a
     225              :     /// temporary path.
     226         3588 :     pub(crate) fn finish_creating(
     227         3588 :         conf: &'static PageServerConf,
     228         3588 :         timeline: &Arc<Timeline>,
     229         3588 :         desc: PersistentLayerDesc,
     230         3588 :         temp_path: &Utf8Path,
     231         3588 :     ) -> anyhow::Result<ResidentLayer> {
     232         3588 :         let mut resident = None;
     233         3588 : 
     234         3588 :         let owner = Layer(Arc::new_cyclic(|owner| {
     235         3588 :             let inner = Arc::new(DownloadedLayer {
     236         3588 :                 owner: owner.clone(),
     237         3588 :                 kind: tokio::sync::OnceCell::default(),
     238         3588 :                 version: 0,
     239         3588 :             });
     240         3588 :             resident = Some(inner.clone());
     241         3588 : 
     242         3588 :             let local_path = local_layer_path(
     243         3588 :                 conf,
     244         3588 :                 &timeline.tenant_shard_id,
     245         3588 :                 &timeline.timeline_id,
     246         3588 :                 &desc.layer_name(),
     247         3588 :                 &timeline.generation,
     248         3588 :             );
     249         3588 : 
     250         3588 :             LayerInner::new(
     251         3588 :                 conf,
     252         3588 :                 timeline,
     253         3588 :                 local_path,
     254         3588 :                 desc,
     255         3588 :                 Some(inner),
     256         3588 :                 timeline.generation,
     257         3588 :                 timeline.get_shard_index(),
     258         3588 :             )
     259         3588 :         }));
     260         3588 : 
     261         3588 :         let downloaded = resident.expect("just initialized");
     262         3588 : 
     263         3588 :         // We never want to overwrite an existing file, so we use `RENAME_NOREPLACE`.
     264         3588 :         // TODO: this leaves the temp file in place if the rename fails, risking us running
     265         3588 :         // out of space. Should we clean it up here or does the calling context deal with this?
     266         3588 :         utils::fs_ext::rename_noreplace(temp_path.as_std_path(), owner.local_path().as_std_path())
     267         3588 :             .with_context(|| format!("rename temporary file as correct path for {owner}"))?;
     268              : 
     269         3588 :         Ok(ResidentLayer { downloaded, owner })
     270         3588 :     }
     271              : 
     272              :     /// Requests the layer to be evicted and waits for this to be done.
     273              :     ///
     274              :     /// If the file is not resident, an [`EvictionError::NotFound`] is returned.
     275              :     ///
     276              :     /// If for a bad luck or blocking of the executor, we miss the actual eviction and the layer is
     277              :     /// re-downloaded, [`EvictionError::Downloaded`] is returned.
     278              :     ///
     279              :     /// Timeout is mandatory, because waiting for eviction is only needed for our tests; eviction
     280              :     /// will happen regardless the future returned by this method completing unless there is a
     281              :     /// read access before eviction gets to complete.
     282              :     ///
     283              :     /// Technically cancellation safe, but cancelling might shift the viewpoint of what generation
     284              :     /// of download-evict cycle on retry.
     285           72 :     pub(crate) async fn evict_and_wait(&self, timeout: Duration) -> Result<(), EvictionError> {
     286           72 :         self.0.evict_and_wait(timeout).await
     287           64 :     }
     288              : 
     289              :     /// Delete the layer file when the `self` gets dropped, also try to schedule a remote index upload
     290              :     /// then.
     291              :     ///
     292              :     /// On drop, this will cause a call to [`crate::tenant::remote_timeline_client::RemoteTimelineClient::schedule_deletion_of_unlinked`].
     293              :     /// This means that the unlinking by [gc] or [compaction] must have happened strictly before
     294              :     /// the value this is called on gets dropped.
     295              :     ///
     296              :     /// This is ensured by both of those methods accepting references to Layer.
     297              :     ///
     298              :     /// [gc]: [`RemoteTimelineClient::schedule_gc_update`]
     299              :     /// [compaction]: [`RemoteTimelineClient::schedule_compaction_update`]
     300         1040 :     pub(crate) fn delete_on_drop(&self) {
     301         1040 :         self.0.delete_on_drop();
     302         1040 :     }
     303              : 
     304       480190 :     pub(crate) async fn get_values_reconstruct_data(
     305       480190 :         &self,
     306       480190 :         keyspace: KeySpace,
     307       480190 :         lsn_range: Range<Lsn>,
     308       480190 :         reconstruct_data: &mut ValuesReconstructState,
     309       480190 :         ctx: &RequestContext,
     310       480190 :     ) -> Result<(), GetVectoredError> {
     311       480190 :         let downloaded = self
     312       480190 :             .0
     313       480190 :             .get_or_maybe_download(true, Some(ctx))
     314       480190 :             .await
     315       480190 :             .map_err(|err| match err {
     316              :                 DownloadError::TimelineShutdown | DownloadError::DownloadCancelled => {
     317            0 :                     GetVectoredError::Cancelled
     318              :                 }
     319            0 :                 other => GetVectoredError::Other(anyhow::anyhow!(other)),
     320       480190 :             })?;
     321       480190 :         let this = ResidentLayer {
     322       480190 :             downloaded: downloaded.clone(),
     323       480190 :             owner: self.clone(),
     324       480190 :         };
     325       480190 : 
     326       480190 :         self.record_access(ctx);
     327       480190 : 
     328       480190 :         downloaded
     329       480190 :             .get_values_reconstruct_data(this, keyspace, lsn_range, reconstruct_data, ctx)
     330       480190 :             .instrument(tracing::debug_span!("get_values_reconstruct_data", layer=%self))
     331       480190 :             .await
     332       480190 :             .map_err(|err| match err {
     333            0 :                 GetVectoredError::Other(err) => GetVectoredError::Other(
     334            0 :                     err.context(format!("get_values_reconstruct_data for layer {self}")),
     335            0 :                 ),
     336            0 :                 err => err,
     337       480190 :             })
     338       480190 :     }
     339              : 
     340              :     /// Download the layer if evicted.
     341              :     ///
     342              :     /// Will not error when the layer is already downloaded.
     343            0 :     pub(crate) async fn download(&self) -> anyhow::Result<()> {
     344            0 :         self.0.get_or_maybe_download(true, None).await?;
     345            0 :         Ok(())
     346            0 :     }
     347              : 
     348          608 :     pub(crate) async fn needs_download(&self) -> Result<Option<NeedsDownload>, std::io::Error> {
     349          608 :         self.0.needs_download().await
     350          608 :     }
     351              : 
     352              :     /// Assuming the layer is already downloaded, returns a guard which will prohibit eviction
     353              :     /// while the guard exists.
     354              :     ///
     355              :     /// Returns None if the layer is currently evicted or becoming evicted.
     356              :     #[cfg(test)]
     357           40 :     pub(crate) async fn keep_resident(&self) -> Option<ResidentLayer> {
     358           40 :         let downloaded = self.0.inner.get().and_then(|rowe| rowe.get())?;
     359              : 
     360           28 :         Some(ResidentLayer {
     361           28 :             downloaded,
     362           28 :             owner: self.clone(),
     363           28 :         })
     364           40 :     }
     365              : 
     366              :     /// Weak indicator of is the layer resident or not. Good enough for eviction, which can deal
     367              :     /// with `EvictionError::NotFound`.
     368              :     ///
     369              :     /// Returns `true` if this layer might be resident, or `false`, if it most likely evicted or
     370              :     /// will be unless a read happens soon.
     371          111 :     pub(crate) fn is_likely_resident(&self) -> bool {
     372          111 :         self.0
     373          111 :             .inner
     374          111 :             .get()
     375          111 :             .map(|rowe| rowe.is_likely_resident())
     376          111 :             .unwrap_or(false)
     377          111 :     }
     378              : 
     379              :     /// Downloads if necessary and creates a guard, which will keep this layer from being evicted.
     380         1132 :     pub(crate) async fn download_and_keep_resident(&self) -> Result<ResidentLayer, DownloadError> {
     381         1132 :         let downloaded = self.0.get_or_maybe_download(true, None).await?;
     382              : 
     383         1132 :         Ok(ResidentLayer {
     384         1132 :             downloaded,
     385         1132 :             owner: self.clone(),
     386         1132 :         })
     387         1132 :     }
     388              : 
     389            0 :     pub(crate) fn info(&self, reset: LayerAccessStatsReset) -> HistoricLayerInfo {
     390            0 :         self.0.info(reset)
     391            0 :     }
     392              : 
     393           16 :     pub(crate) fn latest_activity(&self) -> SystemTime {
     394           16 :         self.0.access_stats.latest_activity()
     395           16 :     }
     396              : 
     397           20 :     pub(crate) fn visibility(&self) -> LayerVisibilityHint {
     398           20 :         self.0.access_stats.visibility()
     399           20 :     }
     400              : 
     401         3592 :     pub(crate) fn local_path(&self) -> &Utf8Path {
     402         3592 :         &self.0.path
     403         3592 :     }
     404              : 
     405         4688 :     pub(crate) fn metadata(&self) -> LayerFileMetadata {
     406         4688 :         self.0.metadata()
     407         4688 :     }
     408              : 
     409            0 :     pub(crate) fn get_timeline_id(&self) -> Option<TimelineId> {
     410            0 :         self.0
     411            0 :             .timeline
     412            0 :             .upgrade()
     413            0 :             .map(|timeline| timeline.timeline_id)
     414            0 :     }
     415              : 
     416              :     /// Traditional debug dumping facility
     417              :     #[allow(unused)]
     418            8 :     pub(crate) async fn dump(&self, verbose: bool, ctx: &RequestContext) -> anyhow::Result<()> {
     419            8 :         self.0.desc.dump();
     420            8 : 
     421            8 :         if verbose {
     422              :             // for now, unconditionally download everything, even if that might not be wanted.
     423            8 :             let l = self.0.get_or_maybe_download(true, Some(ctx)).await?;
     424            8 :             l.dump(&self.0, ctx).await?
     425            0 :         }
     426              : 
     427            8 :         Ok(())
     428            8 :     }
     429              : 
     430              :     /// Waits until this layer has been dropped (and if needed, local file deletion and remote
     431              :     /// deletion scheduling has completed).
     432              :     ///
     433              :     /// Does not start local deletion, use [`Self::delete_on_drop`] for that
     434              :     /// separatedly.
     435              :     #[cfg(any(feature = "testing", test))]
     436            4 :     pub(crate) fn wait_drop(&self) -> impl std::future::Future<Output = ()> + 'static {
     437            4 :         let mut rx = self.0.status.as_ref().unwrap().subscribe();
     438              : 
     439            4 :         async move {
     440              :             loop {
     441            4 :                 if rx.changed().await.is_err() {
     442            4 :                     break;
     443            0 :                 }
     444              :             }
     445            4 :         }
     446            4 :     }
     447              : 
     448       480190 :     fn record_access(&self, ctx: &RequestContext) {
     449       480190 :         if self.0.access_stats.record_access(ctx) {
     450              :             // Visibility was modified to Visible: maybe log about this
     451            0 :             match ctx.task_kind() {
     452              :                 TaskKind::CalculateSyntheticSize
     453              :                 | TaskKind::OndemandLogicalSizeCalculation
     454              :                 | TaskKind::GarbageCollector
     455            0 :                 | TaskKind::MgmtRequest => {
     456            0 :                     // This situation is expected in code paths do binary searches of the LSN space to resolve
     457            0 :                     // an LSN to a timestamp, which happens during GC, during GC cutoff calculations in synthetic size,
     458            0 :                     // and on-demand for certain HTTP API requests. On-demand logical size calculation is also included
     459            0 :                     // because it is run as a sub-task of synthetic size.
     460            0 :                 }
     461              :                 _ => {
     462              :                     // In all other contexts, it is unusual to do I/O involving layers which are not visible at
     463              :                     // some branch tip, so we log the fact that we are accessing something that the visibility
     464              :                     // calculation thought should not be visible.
     465              :                     //
     466              :                     // This case is legal in brief time windows: for example an in-flight getpage request can hold on to a layer object
     467              :                     // which was covered by a concurrent compaction.
     468            0 :                     tracing::info!(
     469              :                         layer=%self,
     470            0 :                         "became visible as a result of access",
     471              :                     );
     472              :                 }
     473              :             }
     474              : 
     475              :             // Update the timeline's visible bytes count
     476            0 :             if let Some(tl) = self.0.timeline.upgrade() {
     477            0 :                 tl.metrics
     478            0 :                     .visible_physical_size_gauge
     479            0 :                     .add(self.0.desc.file_size)
     480            0 :             }
     481       480190 :         }
     482       480190 :     }
     483              : 
     484          692 :     pub(crate) fn set_visibility(&self, visibility: LayerVisibilityHint) {
     485          692 :         let old_visibility = self.0.access_stats.set_visibility(visibility.clone());
     486              :         use LayerVisibilityHint::*;
     487          692 :         match (old_visibility, visibility) {
     488              :             (Visible, Covered) => {
     489              :                 // Subtract this layer's contribution to the visible size metric
     490           72 :                 if let Some(tl) = self.0.timeline.upgrade() {
     491           72 :                     debug_assert!(
     492           72 :                         tl.metrics.visible_physical_size_gauge.get() >= self.0.desc.file_size
     493              :                     );
     494           72 :                     tl.metrics
     495           72 :                         .visible_physical_size_gauge
     496           72 :                         .sub(self.0.desc.file_size)
     497            0 :                 }
     498              :             }
     499              :             (Covered, Visible) => {
     500              :                 // Add this layer's contribution to the visible size metric
     501            0 :                 if let Some(tl) = self.0.timeline.upgrade() {
     502            0 :                     tl.metrics
     503            0 :                         .visible_physical_size_gauge
     504            0 :                         .add(self.0.desc.file_size)
     505            0 :                 }
     506              :             }
     507          620 :             (Covered, Covered) | (Visible, Visible) => {
     508          620 :                 // no change
     509          620 :             }
     510              :         }
     511          692 :     }
     512              : }
     513              : 
     514              : /// The download-ness ([`DownloadedLayer`]) can be either resident or wanted evicted.
     515              : ///
     516              : /// However when we want something evicted, we cannot evict it right away as there might be current
     517              : /// reads happening on it. For example: it has been searched from [`LayerMap::search`] but not yet
     518              : /// read with [`Layer::get_values_reconstruct_data`].
     519              : ///
     520              : /// [`LayerMap::search`]: crate::tenant::layer_map::LayerMap::search
     521              : #[derive(Debug)]
     522              : enum ResidentOrWantedEvicted {
     523              :     Resident(Arc<DownloadedLayer>),
     524              :     WantedEvicted(Weak<DownloadedLayer>, usize),
     525              : }
     526              : 
     527              : impl ResidentOrWantedEvicted {
     528              :     /// Non-mutating access to the a DownloadedLayer, if possible.
     529              :     ///
     530              :     /// This is not used on the read path (anything that calls
     531              :     /// [`LayerInner::get_or_maybe_download`]) because it was decided that reads always win
     532              :     /// evictions, and part of that winning is using [`ResidentOrWantedEvicted::get_and_upgrade`].
     533              :     #[cfg(test)]
     534           28 :     fn get(&self) -> Option<Arc<DownloadedLayer>> {
     535           28 :         match self {
     536           28 :             ResidentOrWantedEvicted::Resident(strong) => Some(strong.clone()),
     537            0 :             ResidentOrWantedEvicted::WantedEvicted(weak, _) => weak.upgrade(),
     538              :         }
     539           28 :     }
     540              : 
     541              :     /// Best-effort query for residency right now, not as strong guarantee as receiving a strong
     542              :     /// reference from `ResidentOrWantedEvicted::get`.
     543           99 :     fn is_likely_resident(&self) -> bool {
     544           99 :         match self {
     545           87 :             ResidentOrWantedEvicted::Resident(_) => true,
     546           12 :             ResidentOrWantedEvicted::WantedEvicted(weak, _) => weak.strong_count() > 0,
     547              :         }
     548           99 :     }
     549              : 
     550              :     /// Upgrades any weak to strong if possible.
     551              :     ///
     552              :     /// Returns a strong reference if possible, along with a boolean telling if an upgrade
     553              :     /// happened.
     554       481338 :     fn get_and_upgrade(&mut self) -> Option<(Arc<DownloadedLayer>, bool)> {
     555       481338 :         match self {
     556       481322 :             ResidentOrWantedEvicted::Resident(strong) => Some((strong.clone(), false)),
     557           16 :             ResidentOrWantedEvicted::WantedEvicted(weak, _) => match weak.upgrade() {
     558            0 :                 Some(strong) => {
     559            0 :                     LAYER_IMPL_METRICS.inc_raced_wanted_evicted_accesses();
     560            0 : 
     561            0 :                     *self = ResidentOrWantedEvicted::Resident(strong.clone());
     562            0 : 
     563            0 :                     Some((strong, true))
     564              :                 }
     565           16 :                 None => None,
     566              :             },
     567              :         }
     568       481338 :     }
     569              : 
     570              :     /// When eviction is first requested, drop down to holding a [`Weak`].
     571              :     ///
     572              :     /// Returns `Some` if this was the first time eviction was requested. Care should be taken to
     573              :     /// drop the possibly last strong reference outside of the mutex of
     574              :     /// [`heavier_once_cell::OnceCell`].
     575           60 :     fn downgrade(&mut self) -> Option<Arc<DownloadedLayer>> {
     576           60 :         match self {
     577           52 :             ResidentOrWantedEvicted::Resident(strong) => {
     578           52 :                 let weak = Arc::downgrade(strong);
     579           52 :                 let mut temp = ResidentOrWantedEvicted::WantedEvicted(weak, strong.version);
     580           52 :                 std::mem::swap(self, &mut temp);
     581           52 :                 match temp {
     582           52 :                     ResidentOrWantedEvicted::Resident(strong) => Some(strong),
     583            0 :                     ResidentOrWantedEvicted::WantedEvicted(..) => unreachable!("just swapped"),
     584              :                 }
     585              :             }
     586            8 :             ResidentOrWantedEvicted::WantedEvicted(..) => None,
     587              :         }
     588           60 :     }
     589              : }
     590              : 
     591              : struct LayerInner {
     592              :     /// Only needed to check ondemand_download_behavior_treat_error_as_warn and creation of
     593              :     /// [`Self::path`].
     594              :     conf: &'static PageServerConf,
     595              : 
     596              :     /// Full path to the file; unclear if this should exist anymore.
     597              :     path: Utf8PathBuf,
     598              : 
     599              :     desc: PersistentLayerDesc,
     600              : 
     601              :     /// Timeline access is needed for remote timeline client and metrics.
     602              :     ///
     603              :     /// There should not be an access to timeline for any reason without entering the
     604              :     /// [`Timeline::gate`] at the same time.
     605              :     timeline: Weak<Timeline>,
     606              : 
     607              :     access_stats: LayerAccessStats,
     608              : 
     609              :     /// This custom OnceCell is backed by std mutex, but only held for short time periods.
     610              :     ///
     611              :     /// Filesystem changes (download, evict) are only done while holding a permit which the
     612              :     /// `heavier_once_cell` provides.
     613              :     ///
     614              :     /// A number of fields in `Layer` are meant to only be updated when holding the InitPermit, but
     615              :     /// possibly read while not holding it.
     616              :     inner: heavier_once_cell::OnceCell<ResidentOrWantedEvicted>,
     617              : 
     618              :     /// Do we want to delete locally and remotely this when `LayerInner` is dropped
     619              :     wanted_deleted: AtomicBool,
     620              : 
     621              :     /// Version is to make sure we will only evict a specific initialization of the downloaded file.
     622              :     ///
     623              :     /// Incremented for each initialization, stored in `DownloadedLayer::version` or
     624              :     /// `ResidentOrWantedEvicted::WantedEvicted`.
     625              :     version: AtomicUsize,
     626              : 
     627              :     /// Allow subscribing to when the layer actually gets evicted, a non-cancellable download
     628              :     /// starts, or completes.
     629              :     ///
     630              :     /// Updates must only be posted while holding the InitPermit or the heavier_once_cell::Guard.
     631              :     /// Holding the InitPermit is the only time we can do state transitions, but we also need to
     632              :     /// cancel a pending eviction on upgrading a [`ResidentOrWantedEvicted::WantedEvicted`] back to
     633              :     /// [`ResidentOrWantedEvicted::Resident`] on access.
     634              :     ///
     635              :     /// The sender is wrapped in an Option to facilitate moving it out on [`LayerInner::drop`].
     636              :     status: Option<tokio::sync::watch::Sender<Status>>,
     637              : 
     638              :     /// Counter for exponential backoff with the download.
     639              :     ///
     640              :     /// This is atomic only for the purposes of having additional data only accessed while holding
     641              :     /// the InitPermit.
     642              :     consecutive_failures: AtomicUsize,
     643              : 
     644              :     /// The generation of this Layer.
     645              :     ///
     646              :     /// For loaded layers (resident or evicted) this comes from [`LayerFileMetadata::generation`],
     647              :     /// for created layers from [`Timeline::generation`].
     648              :     generation: Generation,
     649              : 
     650              :     /// The shard of this Layer.
     651              :     ///
     652              :     /// For layers created in this process, this will always be the [`ShardIndex`] of the
     653              :     /// current `ShardIdentity`` (TODO: add link once it's introduced).
     654              :     ///
     655              :     /// For loaded layers, this may be some other value if the tenant has undergone
     656              :     /// a shard split since the layer was originally written.
     657              :     shard: ShardIndex,
     658              : 
     659              :     /// When the Layer was last evicted but has not been downloaded since.
     660              :     ///
     661              :     /// This is used solely for updating metrics. See [`LayerImplMetrics::redownload_after`].
     662              :     last_evicted_at: std::sync::Mutex<Option<std::time::Instant>>,
     663              : 
     664              :     #[cfg(test)]
     665              :     failpoints: std::sync::Mutex<Vec<failpoints::Failpoint>>,
     666              : }
     667              : 
     668              : impl std::fmt::Display for LayerInner {
     669           60 :     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
     670           60 :         write!(f, "{}", self.layer_desc().short_id())
     671           60 :     }
     672              : }
     673              : 
     674              : impl AsLayerDesc for LayerInner {
     675      3368689 :     fn layer_desc(&self) -> &PersistentLayerDesc {
     676      3368689 :         &self.desc
     677      3368689 :     }
     678              : }
     679              : 
     680              : #[derive(Debug, Clone, Copy)]
     681              : enum Status {
     682              :     Resident,
     683              :     Evicted,
     684              :     Downloading,
     685              : }
     686              : 
     687              : impl Drop for LayerInner {
     688         1416 :     fn drop(&mut self) {
     689         1416 :         // if there was a pending eviction, mark it cancelled here to balance metrics
     690         1416 :         if let Some((ResidentOrWantedEvicted::WantedEvicted(..), _)) = self.inner.take_and_deinit()
     691            4 :         {
     692            4 :             // eviction has already been started
     693            4 :             LAYER_IMPL_METRICS.inc_eviction_cancelled(EvictionCancelled::LayerGone);
     694            4 : 
     695            4 :             // eviction request is intentionally not honored as no one is present to wait for it
     696            4 :             // and we could be delaying shutdown for nothing.
     697         1412 :         }
     698              : 
     699         1416 :         let timeline = self.timeline.upgrade();
     700              : 
     701         1416 :         if let Some(timeline) = timeline.as_ref() {
     702              :             // Only need to decrement metrics if the timeline still exists: otherwise
     703              :             // it will have already de-registered these metrics via TimelineMetrics::shutdown
     704         1384 :             if self.desc.is_delta() {
     705         1241 :                 timeline.metrics.layer_count_delta.dec();
     706         1241 :                 timeline.metrics.layer_size_delta.sub(self.desc.file_size);
     707         1241 :             } else {
     708          143 :                 timeline.metrics.layer_count_image.dec();
     709          143 :                 timeline.metrics.layer_size_image.sub(self.desc.file_size);
     710          143 :             }
     711              : 
     712         1384 :             if matches!(self.access_stats.visibility(), LayerVisibilityHint::Visible) {
     713         1384 :                 debug_assert!(
     714         1384 :                     timeline.metrics.visible_physical_size_gauge.get() >= self.desc.file_size
     715              :                 );
     716         1384 :                 timeline
     717         1384 :                     .metrics
     718         1384 :                     .visible_physical_size_gauge
     719         1384 :                     .sub(self.desc.file_size);
     720            0 :             }
     721           32 :         }
     722              : 
     723         1416 :         if !*self.wanted_deleted.get_mut() {
     724          392 :             return;
     725         1024 :         }
     726              : 
     727         1024 :         let span = tracing::info_span!(parent: None, "layer_delete", tenant_id = %self.layer_desc().tenant_shard_id.tenant_id, shard_id=%self.layer_desc().tenant_shard_id.shard_slug(), timeline_id = %self.layer_desc().timeline_id);
     728              : 
     729         1024 :         let path = std::mem::take(&mut self.path);
     730         1024 :         let file_name = self.layer_desc().layer_name();
     731         1024 :         let file_size = self.layer_desc().file_size;
     732         1024 :         let meta = self.metadata();
     733         1024 :         let status = self.status.take();
     734         1024 : 
     735         1024 :         Self::spawn_blocking(move || {
     736         1024 :             let _g = span.entered();
     737         1024 : 
     738         1024 :             // carry this until we are finished for [`Layer::wait_drop`] support
     739         1024 :             let _status = status;
     740              : 
     741         1024 :             let Some(timeline) = timeline else {
     742              :                 // no need to nag that timeline is gone: under normal situation on
     743              :                 // task_mgr::remove_tenant_from_memory the timeline is gone before we get dropped.
     744            0 :                 LAYER_IMPL_METRICS.inc_deletes_failed(DeleteFailed::TimelineGone);
     745            0 :                 return;
     746              :             };
     747              : 
     748         1024 :             let Ok(_guard) = timeline.gate.enter() else {
     749            0 :                 LAYER_IMPL_METRICS.inc_deletes_failed(DeleteFailed::TimelineGone);
     750            0 :                 return;
     751              :             };
     752              : 
     753         1024 :             let removed = match std::fs::remove_file(path) {
     754         1020 :                 Ok(()) => true,
     755            4 :                 Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
     756            4 :                     // until we no longer do detaches by removing all local files before removing the
     757            4 :                     // tenant from the global map, we will always get these errors even if we knew what
     758            4 :                     // is the latest state.
     759            4 :                     //
     760            4 :                     // we currently do not track the latest state, so we'll also end up here on evicted
     761            4 :                     // layers.
     762            4 :                     false
     763              :                 }
     764            0 :                 Err(e) => {
     765            0 :                     tracing::error!("failed to remove wanted deleted layer: {e}");
     766            0 :                     LAYER_IMPL_METRICS.inc_delete_removes_failed();
     767            0 :                     false
     768              :                 }
     769              :             };
     770              : 
     771         1024 :             if removed {
     772         1020 :                 timeline.metrics.resident_physical_size_sub(file_size);
     773         1020 :             }
     774         1024 :             let res = timeline
     775         1024 :                 .remote_client
     776         1024 :                 .schedule_deletion_of_unlinked(vec![(file_name, meta)]);
     777              : 
     778         1024 :             if let Err(e) = res {
     779              :                 // test_timeline_deletion_with_files_stuck_in_upload_queue is good at
     780              :                 // demonstrating this deadlock (without spawn_blocking): stop will drop
     781              :                 // queued items, which will have ResidentLayer's, and those drops would try
     782              :                 // to re-entrantly lock the RemoteTimelineClient inner state.
     783            4 :                 if !timeline.is_active() {
     784            4 :                     tracing::info!("scheduling deletion on drop failed: {e:#}");
     785              :                 } else {
     786            0 :                     tracing::warn!("scheduling deletion on drop failed: {e:#}");
     787              :                 }
     788            0 :                 LAYER_IMPL_METRICS.inc_deletes_failed(DeleteFailed::DeleteSchedulingFailed);
     789         1020 :             } else {
     790         1020 :                 LAYER_IMPL_METRICS.inc_completed_deletes();
     791         1020 :             }
     792         1024 :         });
     793         1416 :     }
     794              : }
     795              : 
     796              : impl LayerInner {
     797              :     #[allow(clippy::too_many_arguments)]
     798         3832 :     fn new(
     799         3832 :         conf: &'static PageServerConf,
     800         3832 :         timeline: &Arc<Timeline>,
     801         3832 :         local_path: Utf8PathBuf,
     802         3832 :         desc: PersistentLayerDesc,
     803         3832 :         downloaded: Option<Arc<DownloadedLayer>>,
     804         3832 :         generation: Generation,
     805         3832 :         shard: ShardIndex,
     806         3832 :     ) -> Self {
     807         3832 :         let (inner, version, init_status) = if let Some(inner) = downloaded {
     808         3832 :             let version = inner.version;
     809         3832 :             let resident = ResidentOrWantedEvicted::Resident(inner);
     810         3832 :             (
     811         3832 :                 heavier_once_cell::OnceCell::new(resident),
     812         3832 :                 version,
     813         3832 :                 Status::Resident,
     814         3832 :             )
     815              :         } else {
     816            0 :             (heavier_once_cell::OnceCell::default(), 0, Status::Evicted)
     817              :         };
     818              : 
     819              :         // This object acts as a RAII guard on these metrics: increment on construction
     820         3832 :         if desc.is_delta() {
     821         3116 :             timeline.metrics.layer_count_delta.inc();
     822         3116 :             timeline.metrics.layer_size_delta.add(desc.file_size);
     823         3116 :         } else {
     824          716 :             timeline.metrics.layer_count_image.inc();
     825          716 :             timeline.metrics.layer_size_image.add(desc.file_size);
     826          716 :         }
     827              : 
     828              :         // New layers are visible by default. This metric is later updated on drop or in set_visibility
     829         3832 :         timeline
     830         3832 :             .metrics
     831         3832 :             .visible_physical_size_gauge
     832         3832 :             .add(desc.file_size);
     833         3832 : 
     834         3832 :         LayerInner {
     835         3832 :             conf,
     836         3832 :             path: local_path,
     837         3832 :             desc,
     838         3832 :             timeline: Arc::downgrade(timeline),
     839         3832 :             access_stats: Default::default(),
     840         3832 :             wanted_deleted: AtomicBool::new(false),
     841         3832 :             inner,
     842         3832 :             version: AtomicUsize::new(version),
     843         3832 :             status: Some(tokio::sync::watch::channel(init_status).0),
     844         3832 :             consecutive_failures: AtomicUsize::new(0),
     845         3832 :             generation,
     846         3832 :             shard,
     847         3832 :             last_evicted_at: std::sync::Mutex::default(),
     848         3832 :             #[cfg(test)]
     849         3832 :             failpoints: Default::default(),
     850         3832 :         }
     851         3832 :     }
     852              : 
     853         1040 :     fn delete_on_drop(&self) {
     854         1040 :         let res =
     855         1040 :             self.wanted_deleted
     856         1040 :                 .compare_exchange(false, true, Ordering::Release, Ordering::Relaxed);
     857         1040 : 
     858         1040 :         if res.is_ok() {
     859         1032 :             LAYER_IMPL_METRICS.inc_started_deletes();
     860         1032 :         }
     861         1040 :     }
     862              : 
     863              :     /// Cancellation safe, however dropping the future and calling this method again might result
     864              :     /// in a new attempt to evict OR join the previously started attempt.
     865           72 :     #[tracing::instrument(level = tracing::Level::DEBUG, skip_all, ret, err(level = tracing::Level::DEBUG), fields(layer=%self))]
     866              :     pub(crate) async fn evict_and_wait(&self, timeout: Duration) -> Result<(), EvictionError> {
     867              :         let mut rx = self.status.as_ref().unwrap().subscribe();
     868              : 
     869              :         {
     870              :             let current = rx.borrow_and_update();
     871              :             match &*current {
     872              :                 Status::Resident => {
     873              :                     // we might get lucky and evict this; continue
     874              :                 }
     875              :                 Status::Evicted | Status::Downloading => {
     876              :                     // it is already evicted
     877              :                     return Err(EvictionError::NotFound);
     878              :                 }
     879              :             }
     880              :         }
     881              : 
     882              :         let strong = {
     883              :             match self.inner.get() {
     884              :                 Some(mut either) => either.downgrade(),
     885              :                 None => {
     886              :                     // we already have a scheduled eviction, which just has not gotten to run yet.
     887              :                     // it might still race with a read access, but that could also get cancelled,
     888              :                     // so let's say this is not evictable.
     889              :                     return Err(EvictionError::NotFound);
     890              :                 }
     891              :             }
     892              :         };
     893              : 
     894              :         if strong.is_some() {
     895              :             // drop the DownloadedLayer outside of the holding the guard
     896              :             drop(strong);
     897              : 
     898              :             // idea here is that only one evicter should ever get to witness a strong reference,
     899              :             // which means whenever get_or_maybe_download upgrades a weak, it must mark up a
     900              :             // cancelled eviction and signal us, like it currently does.
     901              :             //
     902              :             // a second concurrent evict_and_wait will not see a strong reference.
     903              :             LAYER_IMPL_METRICS.inc_started_evictions();
     904              :         }
     905              : 
     906              :         let changed = rx.changed();
     907              :         let changed = tokio::time::timeout(timeout, changed).await;
     908              : 
     909              :         let Ok(changed) = changed else {
     910              :             return Err(EvictionError::Timeout);
     911              :         };
     912              : 
     913              :         let _: () = changed.expect("cannot be closed, because we are holding a strong reference");
     914              : 
     915              :         let current = rx.borrow_and_update();
     916              : 
     917              :         match &*current {
     918              :             // the easiest case
     919              :             Status::Evicted => Ok(()),
     920              :             // it surely was evicted in between, but then there was a new access now; we can't know
     921              :             // if it'll succeed so lets just call it evicted
     922              :             Status::Downloading => Ok(()),
     923              :             // either the download which was started after eviction completed already, or it was
     924              :             // never evicted
     925              :             Status::Resident => Err(EvictionError::Downloaded),
     926              :         }
     927              :     }
     928              : 
     929              :     /// Cancellation safe.
     930       481354 :     async fn get_or_maybe_download(
     931       481354 :         self: &Arc<Self>,
     932       481354 :         allow_download: bool,
     933       481354 :         ctx: Option<&RequestContext>,
     934       481354 :     ) -> Result<Arc<DownloadedLayer>, DownloadError> {
     935           32 :         let (weak, permit) = {
     936              :             // get_or_init_detached can:
     937              :             // - be fast (mutex lock) OR uncontested semaphore permit acquire
     938              :             // - be slow (wait for semaphore permit or closing)
     939       481354 :             let init_cancelled = scopeguard::guard((), |_| LAYER_IMPL_METRICS.inc_init_cancelled());
     940              : 
     941       481354 :             let locked = self
     942       481354 :                 .inner
     943       481354 :                 .get_or_init_detached()
     944       481354 :                 .await
     945       481354 :                 .map(|mut guard| guard.get_and_upgrade().ok_or(guard));
     946       481354 : 
     947       481354 :             scopeguard::ScopeGuard::into_inner(init_cancelled);
     948              : 
     949       481322 :             match locked {
     950              :                 // this path could had been a RwLock::read
     951       481322 :                 Ok(Ok((strong, upgraded))) if !upgraded => return Ok(strong),
     952            0 :                 Ok(Ok((strong, _))) => {
     953            0 :                     // when upgraded back, the Arc<DownloadedLayer> is still available, but
     954            0 :                     // previously a `evict_and_wait` was received. this is the only place when we
     955            0 :                     // send out an update without holding the InitPermit.
     956            0 :                     //
     957            0 :                     // note that we also have dropped the Guard; this is fine, because we just made
     958            0 :                     // a state change and are holding a strong reference to be returned.
     959            0 :                     self.status.as_ref().unwrap().send_replace(Status::Resident);
     960            0 :                     LAYER_IMPL_METRICS
     961            0 :                         .inc_eviction_cancelled(EvictionCancelled::UpgradedBackOnAccess);
     962            0 : 
     963            0 :                     return Ok(strong);
     964              :                 }
     965           16 :                 Ok(Err(guard)) => {
     966           16 :                     // path to here: we won the eviction, the file should still be on the disk.
     967           16 :                     let (weak, permit) = guard.take_and_deinit();
     968           16 :                     (Some(weak), permit)
     969              :                 }
     970           16 :                 Err(permit) => (None, permit),
     971              :             }
     972              :         };
     973              : 
     974           32 :         if let Some(weak) = weak {
     975              :             // only drop the weak after dropping the heavier_once_cell guard
     976           16 :             assert!(
     977           16 :                 matches!(weak, ResidentOrWantedEvicted::WantedEvicted(..)),
     978            0 :                 "unexpected {weak:?}, ResidentOrWantedEvicted::get_and_upgrade has a bug"
     979              :             );
     980           16 :         }
     981              : 
     982           32 :         let timeline = self
     983           32 :             .timeline
     984           32 :             .upgrade()
     985           32 :             .ok_or(DownloadError::TimelineShutdown)?;
     986              : 
     987              :         // count cancellations, which currently remain largely unexpected
     988           32 :         let init_cancelled = scopeguard::guard((), |_| LAYER_IMPL_METRICS.inc_init_cancelled());
     989              : 
     990              :         // check if we really need to be downloaded: this can happen if a read access won the
     991              :         // semaphore before eviction.
     992              :         //
     993              :         // if we are cancelled while doing this `stat` the `self.inner` will be uninitialized. a
     994              :         // pending eviction will try to evict even upon finding an uninitialized `self.inner`.
     995           32 :         let needs_download = self
     996           32 :             .needs_download()
     997           32 :             .await
     998           32 :             .map_err(DownloadError::PreStatFailed);
     999           32 : 
    1000           32 :         scopeguard::ScopeGuard::into_inner(init_cancelled);
    1001              : 
    1002           32 :         let needs_download = needs_download?;
    1003              : 
    1004           32 :         let Some(reason) = needs_download else {
    1005              :             // the file is present locally because eviction has not had a chance to run yet
    1006              : 
    1007              :             #[cfg(test)]
    1008           16 :             self.failpoint(failpoints::FailpointKind::AfterDeterminingLayerNeedsNoDownload)
    1009           16 :                 .await?;
    1010              : 
    1011           12 :             LAYER_IMPL_METRICS.inc_init_needed_no_download();
    1012           12 : 
    1013           12 :             return Ok(self.initialize_after_layer_is_on_disk(permit));
    1014              :         };
    1015              : 
    1016              :         // we must download; getting cancelled before spawning the download is not an issue as
    1017              :         // any still running eviction would not find anything to evict.
    1018              : 
    1019           16 :         if let NeedsDownload::NotFile(ft) = reason {
    1020            0 :             return Err(DownloadError::NotFile(ft));
    1021           16 :         }
    1022              : 
    1023           16 :         if let Some(ctx) = ctx {
    1024            4 :             self.check_expected_download(ctx)?;
    1025           12 :         }
    1026              : 
    1027           16 :         if !allow_download {
    1028              :             // this is only used from tests, but it is hard to test without the boolean
    1029            4 :             return Err(DownloadError::DownloadRequired);
    1030           12 :         }
    1031           12 : 
    1032           12 :         let download_ctx = ctx
    1033           12 :             .map(|ctx| ctx.detached_child(TaskKind::LayerDownload, DownloadBehavior::Download))
    1034           12 :             .unwrap_or(RequestContext::new(
    1035           12 :                 TaskKind::LayerDownload,
    1036           12 :                 DownloadBehavior::Download,
    1037           12 :             ));
    1038              : 
    1039           12 :         async move {
    1040           12 :             tracing::info!(%reason, "downloading on-demand");
    1041              : 
    1042           12 :             let init_cancelled = scopeguard::guard((), |_| LAYER_IMPL_METRICS.inc_init_cancelled());
    1043           12 :             let res = self
    1044           12 :                 .download_init_and_wait(timeline, permit, download_ctx)
    1045           12 :                 .await?;
    1046           12 :             scopeguard::ScopeGuard::into_inner(init_cancelled);
    1047           12 :             Ok(res)
    1048           12 :         }
    1049           12 :         .instrument(tracing::info_span!("get_or_maybe_download", layer=%self))
    1050           12 :         .await
    1051       481354 :     }
    1052              : 
    1053              :     /// Nag or fail per RequestContext policy
    1054            4 :     fn check_expected_download(&self, ctx: &RequestContext) -> Result<(), DownloadError> {
    1055              :         use crate::context::DownloadBehavior::*;
    1056            4 :         let b = ctx.download_behavior();
    1057            4 :         match b {
    1058            4 :             Download => Ok(()),
    1059              :             Warn | Error => {
    1060            0 :                 tracing::info!(
    1061            0 :                     "unexpectedly on-demand downloading for task kind {:?}",
    1062            0 :                     ctx.task_kind()
    1063              :                 );
    1064            0 :                 crate::metrics::UNEXPECTED_ONDEMAND_DOWNLOADS.inc();
    1065              : 
    1066            0 :                 let really_error =
    1067            0 :                     matches!(b, Error) && !self.conf.ondemand_download_behavior_treat_error_as_warn;
    1068              : 
    1069            0 :                 if really_error {
    1070              :                     // this check is only probablistic, seems like flakyness footgun
    1071            0 :                     Err(DownloadError::ContextAndConfigReallyDeniesDownloads)
    1072              :                 } else {
    1073            0 :                     Ok(())
    1074              :                 }
    1075              :             }
    1076              :         }
    1077            4 :     }
    1078              : 
    1079              :     /// Actual download, at most one is executed at the time.
    1080           12 :     async fn download_init_and_wait(
    1081           12 :         self: &Arc<Self>,
    1082           12 :         timeline: Arc<Timeline>,
    1083           12 :         permit: heavier_once_cell::InitPermit,
    1084           12 :         ctx: RequestContext,
    1085           12 :     ) -> Result<Arc<DownloadedLayer>, DownloadError> {
    1086           12 :         debug_assert_current_span_has_tenant_and_timeline_id();
    1087           12 : 
    1088           12 :         let (tx, rx) = tokio::sync::oneshot::channel();
    1089           12 : 
    1090           12 :         let this: Arc<Self> = self.clone();
    1091              : 
    1092           12 :         let guard = timeline
    1093           12 :             .gate
    1094           12 :             .enter()
    1095           12 :             .map_err(|_| DownloadError::DownloadCancelled)?;
    1096              : 
    1097           12 :         Self::spawn(
    1098           12 :             async move {
    1099            0 :                 let _guard = guard;
    1100            0 : 
    1101            0 :                 // now that we have commited to downloading, send out an update to:
    1102            0 :                 // - unhang any pending eviction
    1103            0 :                 // - break out of evict_and_wait
    1104            0 :                 this.status
    1105            0 :                     .as_ref()
    1106            0 :                     .unwrap()
    1107            0 :                     .send_replace(Status::Downloading);
    1108           12 : 
    1109           12 :                 #[cfg(test)]
    1110           12 :                 this.failpoint(failpoints::FailpointKind::WaitBeforeDownloading)
    1111           12 :                     .await
    1112           12 :                     .unwrap();
    1113              : 
    1114           12 :                 let res = this.download_and_init(timeline, permit, &ctx).await;
    1115              : 
    1116           12 :                 if let Err(res) = tx.send(res) {
    1117            0 :                     match res {
    1118            0 :                         Ok(_res) => {
    1119            0 :                             tracing::debug!("layer initialized, but caller has been cancelled");
    1120            0 :                             LAYER_IMPL_METRICS.inc_init_completed_without_requester();
    1121              :                         }
    1122            0 :                         Err(e) => {
    1123            0 :                             tracing::info!(
    1124            0 :                                 "layer file download failed, and caller has been cancelled: {e:?}"
    1125              :                             );
    1126            0 :                             LAYER_IMPL_METRICS.inc_download_failed_without_requester();
    1127              :                         }
    1128              :                     }
    1129           12 :                 }
    1130           12 :             }
    1131           12 :             .in_current_span(),
    1132           12 :         );
    1133           12 : 
    1134           12 :         match rx.await {
    1135           12 :             Ok(Ok(res)) => Ok(res),
    1136              :             Ok(Err(remote_storage::DownloadError::Cancelled)) => {
    1137            0 :                 Err(DownloadError::DownloadCancelled)
    1138              :             }
    1139            0 :             Ok(Err(_)) => Err(DownloadError::DownloadFailed),
    1140            0 :             Err(_gone) => Err(DownloadError::DownloadCancelled),
    1141              :         }
    1142           12 :     }
    1143              : 
    1144           12 :     async fn download_and_init(
    1145           12 :         self: &Arc<LayerInner>,
    1146           12 :         timeline: Arc<Timeline>,
    1147           12 :         permit: heavier_once_cell::InitPermit,
    1148           12 :         ctx: &RequestContext,
    1149           12 :     ) -> Result<Arc<DownloadedLayer>, remote_storage::DownloadError> {
    1150           12 :         let result = timeline
    1151           12 :             .remote_client
    1152           12 :             .download_layer_file(
    1153           12 :                 &self.desc.layer_name(),
    1154           12 :                 &self.metadata(),
    1155           12 :                 &self.path,
    1156           12 :                 &timeline.gate,
    1157           12 :                 &timeline.cancel,
    1158           12 :                 ctx,
    1159           12 :             )
    1160           12 :             .await;
    1161              : 
    1162           12 :         match result {
    1163           12 :             Ok(size) => {
    1164           12 :                 assert_eq!(size, self.desc.file_size);
    1165              : 
    1166           12 :                 match self.needs_download().await {
    1167            0 :                     Ok(Some(reason)) => {
    1168            0 :                         // this is really a bug in needs_download or remote timeline client
    1169            0 :                         panic!("post-condition failed: needs_download returned {reason:?}");
    1170              :                     }
    1171           12 :                     Ok(None) => {
    1172           12 :                         // as expected
    1173           12 :                     }
    1174            0 :                     Err(e) => {
    1175            0 :                         panic!("post-condition failed: needs_download errored: {e:?}");
    1176              :                     }
    1177              :                 }
    1178              : 
    1179           12 :                 tracing::info!(size=%self.desc.file_size, "on-demand download successful");
    1180           12 :                 timeline
    1181           12 :                     .metrics
    1182           12 :                     .resident_physical_size_add(self.desc.file_size);
    1183           12 :                 self.consecutive_failures.store(0, Ordering::Relaxed);
    1184           12 : 
    1185           12 :                 let since_last_eviction = self
    1186           12 :                     .last_evicted_at
    1187           12 :                     .lock()
    1188           12 :                     .unwrap()
    1189           12 :                     .take()
    1190           12 :                     .map(|ts| ts.elapsed());
    1191           12 :                 if let Some(since_last_eviction) = since_last_eviction {
    1192           12 :                     LAYER_IMPL_METRICS.record_redownloaded_after(since_last_eviction);
    1193           12 :                 }
    1194              : 
    1195           12 :                 self.access_stats.record_residence_event();
    1196           12 : 
    1197           12 :                 Ok(self.initialize_after_layer_is_on_disk(permit))
    1198              :             }
    1199            0 :             Err(e) => {
    1200            0 :                 let consecutive_failures =
    1201            0 :                     1 + self.consecutive_failures.fetch_add(1, Ordering::Relaxed);
    1202            0 : 
    1203            0 :                 if timeline.cancel.is_cancelled() {
    1204              :                     // If we're shutting down, drop out before logging the error
    1205            0 :                     return Err(e);
    1206            0 :                 }
    1207            0 : 
    1208            0 :                 tracing::error!(consecutive_failures, "layer file download failed: {e:#}");
    1209              : 
    1210            0 :                 let backoff = utils::backoff::exponential_backoff_duration_seconds(
    1211            0 :                     consecutive_failures.min(u32::MAX as usize) as u32,
    1212            0 :                     1.5,
    1213            0 :                     60.0,
    1214            0 :                 );
    1215            0 : 
    1216            0 :                 let backoff = std::time::Duration::from_secs_f64(backoff);
    1217            0 : 
    1218            0 :                 tokio::select! {
    1219            0 :                     _ = tokio::time::sleep(backoff) => {},
    1220            0 :                     _ = timeline.cancel.cancelled() => {},
    1221              :                 };
    1222              : 
    1223            0 :                 Err(e)
    1224              :             }
    1225              :         }
    1226           12 :     }
    1227              : 
    1228              :     /// Initializes the `Self::inner` to a "resident" state.
    1229              :     ///
    1230              :     /// Callers are assumed to ensure that the file is actually on disk with `Self::needs_download`
    1231              :     /// before calling this method.
    1232              :     ///
    1233              :     /// If this method is ever made async, it needs to be cancellation safe so that no state
    1234              :     /// changes are made before we can write to the OnceCell in non-cancellable fashion.
    1235           24 :     fn initialize_after_layer_is_on_disk(
    1236           24 :         self: &Arc<LayerInner>,
    1237           24 :         permit: heavier_once_cell::InitPermit,
    1238           24 :     ) -> Arc<DownloadedLayer> {
    1239           24 :         debug_assert_current_span_has_tenant_and_timeline_id();
    1240           24 : 
    1241           24 :         // disable any scheduled but not yet running eviction deletions for this initialization
    1242           24 :         let next_version = 1 + self.version.fetch_add(1, Ordering::Relaxed);
    1243           24 :         self.status.as_ref().unwrap().send_replace(Status::Resident);
    1244           24 : 
    1245           24 :         let res = Arc::new(DownloadedLayer {
    1246           24 :             owner: Arc::downgrade(self),
    1247           24 :             kind: tokio::sync::OnceCell::default(),
    1248           24 :             version: next_version,
    1249           24 :         });
    1250           24 : 
    1251           24 :         let waiters = self.inner.initializer_count();
    1252           24 :         if waiters > 0 {
    1253            0 :             tracing::info!(waiters, "completing layer init for other tasks");
    1254           24 :         }
    1255              : 
    1256           24 :         let value = ResidentOrWantedEvicted::Resident(res.clone());
    1257           24 : 
    1258           24 :         self.inner.set(value, permit);
    1259           24 : 
    1260           24 :         res
    1261           24 :     }
    1262              : 
    1263          656 :     async fn needs_download(&self) -> Result<Option<NeedsDownload>, std::io::Error> {
    1264          656 :         match tokio::fs::metadata(&self.path).await {
    1265          640 :             Ok(m) => Ok(self.is_file_present_and_good_size(&m).err()),
    1266           16 :             Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(Some(NeedsDownload::NotFound)),
    1267            0 :             Err(e) => Err(e),
    1268              :         }
    1269          656 :     }
    1270              : 
    1271          244 :     fn needs_download_blocking(&self) -> Result<Option<NeedsDownload>, std::io::Error> {
    1272          244 :         match self.path.metadata() {
    1273          244 :             Ok(m) => Ok(self.is_file_present_and_good_size(&m).err()),
    1274            0 :             Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(Some(NeedsDownload::NotFound)),
    1275            0 :             Err(e) => Err(e),
    1276              :         }
    1277          244 :     }
    1278              : 
    1279          884 :     fn is_file_present_and_good_size(&self, m: &std::fs::Metadata) -> Result<(), NeedsDownload> {
    1280          884 :         // in future, this should include sha2-256 validation of the file.
    1281          884 :         if !m.is_file() {
    1282            0 :             Err(NeedsDownload::NotFile(m.file_type()))
    1283          884 :         } else if m.len() != self.desc.file_size {
    1284            0 :             Err(NeedsDownload::WrongSize {
    1285            0 :                 actual: m.len(),
    1286            0 :                 expected: self.desc.file_size,
    1287            0 :             })
    1288              :         } else {
    1289          884 :             Ok(())
    1290              :         }
    1291          884 :     }
    1292              : 
    1293            0 :     fn info(&self, reset: LayerAccessStatsReset) -> HistoricLayerInfo {
    1294            0 :         let layer_name = self.desc.layer_name().to_string();
    1295            0 : 
    1296            0 :         let resident = self
    1297            0 :             .inner
    1298            0 :             .get()
    1299            0 :             .map(|rowe| rowe.is_likely_resident())
    1300            0 :             .unwrap_or(false);
    1301            0 : 
    1302            0 :         let access_stats = self.access_stats.as_api_model(reset);
    1303            0 : 
    1304            0 :         if self.desc.is_delta {
    1305            0 :             let lsn_range = &self.desc.lsn_range;
    1306            0 : 
    1307            0 :             HistoricLayerInfo::Delta {
    1308            0 :                 layer_file_name: layer_name,
    1309            0 :                 layer_file_size: self.desc.file_size,
    1310            0 :                 lsn_start: lsn_range.start,
    1311            0 :                 lsn_end: lsn_range.end,
    1312            0 :                 remote: !resident,
    1313            0 :                 access_stats,
    1314            0 :                 l0: crate::tenant::layer_map::LayerMap::is_l0(
    1315            0 :                     &self.layer_desc().key_range,
    1316            0 :                     self.layer_desc().is_delta,
    1317            0 :                 ),
    1318            0 :             }
    1319              :         } else {
    1320            0 :             let lsn = self.desc.image_layer_lsn();
    1321            0 : 
    1322            0 :             HistoricLayerInfo::Image {
    1323            0 :                 layer_file_name: layer_name,
    1324            0 :                 layer_file_size: self.desc.file_size,
    1325            0 :                 lsn_start: lsn,
    1326            0 :                 remote: !resident,
    1327            0 :                 access_stats,
    1328            0 :             }
    1329              :         }
    1330            0 :     }
    1331              : 
    1332              :     /// `DownloadedLayer` is being dropped, so it calls this method.
    1333           48 :     fn on_downloaded_layer_drop(self: Arc<LayerInner>, only_version: usize) {
    1334              :         // we cannot know without inspecting LayerInner::inner if we should evict or not, even
    1335              :         // though here it is very likely
    1336           48 :         let span = tracing::info_span!(parent: None, "layer_evict", tenant_id = %self.desc.tenant_shard_id.tenant_id, shard_id = %self.desc.tenant_shard_id.shard_slug(), timeline_id = %self.desc.timeline_id, layer=%self, version=%only_version);
    1337              : 
    1338              :         // NOTE: this scope *must* never call `self.inner.get` because evict_and_wait might
    1339              :         // drop while the `self.inner` is being locked, leading to a deadlock.
    1340              : 
    1341           48 :         let start_evicting = async move {
    1342           48 :             #[cfg(test)]
    1343           48 :             self.failpoint(failpoints::FailpointKind::WaitBeforeStartingEvicting)
    1344           48 :                 .await
    1345           48 :                 .expect("failpoint should not have errored");
    1346           48 : 
    1347           48 :             tracing::debug!("eviction started");
    1348              : 
    1349           48 :             let res = self.wait_for_turn_and_evict(only_version).await;
    1350              :             // metrics: ignore the Ok branch, it is not done yet
    1351           48 :             if let Err(e) = res {
    1352           12 :                 tracing::debug!(res=?Err::<(), _>(&e), "eviction completed");
    1353           12 :                 LAYER_IMPL_METRICS.inc_eviction_cancelled(e);
    1354           36 :             }
    1355           48 :         };
    1356              : 
    1357           48 :         Self::spawn(start_evicting.instrument(span));
    1358           48 :     }
    1359              : 
    1360           48 :     async fn wait_for_turn_and_evict(
    1361           48 :         self: Arc<LayerInner>,
    1362           48 :         only_version: usize,
    1363           48 :     ) -> Result<(), EvictionCancelled> {
    1364           92 :         fn is_good_to_continue(status: &Status) -> Result<(), EvictionCancelled> {
    1365              :             use Status::*;
    1366           92 :             match status {
    1367           88 :                 Resident => Ok(()),
    1368            4 :                 Evicted => Err(EvictionCancelled::UnexpectedEvictedState),
    1369            0 :                 Downloading => Err(EvictionCancelled::LostToDownload),
    1370              :             }
    1371           92 :         }
    1372              : 
    1373           48 :         let timeline = self
    1374           48 :             .timeline
    1375           48 :             .upgrade()
    1376           48 :             .ok_or(EvictionCancelled::TimelineGone)?;
    1377              : 
    1378           48 :         let mut rx = self
    1379           48 :             .status
    1380           48 :             .as_ref()
    1381           48 :             .expect("LayerInner cannot be dropped, holding strong ref")
    1382           48 :             .subscribe();
    1383           48 : 
    1384           48 :         is_good_to_continue(&rx.borrow_and_update())?;
    1385              : 
    1386           44 :         let Ok(gate) = timeline.gate.enter() else {
    1387            0 :             return Err(EvictionCancelled::TimelineGone);
    1388              :         };
    1389              : 
    1390           36 :         let permit = {
    1391              :             // we cannot just `std::fs::remove_file` because there might already be an
    1392              :             // get_or_maybe_download which will inspect filesystem and reinitialize. filesystem
    1393              :             // operations must be done while holding the heavier_once_cell::InitPermit
    1394           44 :             let mut wait = std::pin::pin!(self.inner.get_or_init_detached());
    1395              : 
    1396           44 :             let waited = loop {
    1397              :                 // we must race to the Downloading starting, otherwise we would have to wait until the
    1398              :                 // completion of the download. waiting for download could be long and hinder our
    1399              :                 // efforts to alert on "hanging" evictions.
    1400           44 :                 tokio::select! {
    1401           44 :                     res = &mut wait => break res,
    1402           44 :                     _ = rx.changed() => {
    1403            0 :                         is_good_to_continue(&rx.borrow_and_update())?;
    1404              :                         // two possibilities for Status::Resident:
    1405              :                         // - the layer was found locally from disk by a read
    1406              :                         // - we missed a bunch of updates and now the layer is
    1407              :                         // again downloaded -- assume we'll fail later on with
    1408              :                         // version check or AlreadyReinitialized
    1409              :                     }
    1410              :                 }
    1411              :             };
    1412              : 
    1413              :             // re-check now that we have the guard or permit; all updates should have happened
    1414              :             // while holding the permit.
    1415           44 :             is_good_to_continue(&rx.borrow_and_update())?;
    1416              : 
    1417              :             // the term deinitialize is used here, because we clearing out the Weak will eventually
    1418              :             // lead to deallocating the reference counted value, and the value we
    1419              :             // `Guard::take_and_deinit` is likely to be the last because the Weak is never cloned.
    1420           44 :             let (_weak, permit) = match waited {
    1421           40 :                 Ok(guard) => {
    1422           40 :                     match &*guard {
    1423           36 :                         ResidentOrWantedEvicted::WantedEvicted(_weak, version)
    1424           36 :                             if *version == only_version =>
    1425           32 :                         {
    1426           32 :                             tracing::debug!(version, "deinitializing matching WantedEvicted");
    1427           32 :                             let (weak, permit) = guard.take_and_deinit();
    1428           32 :                             (Some(weak), permit)
    1429              :                         }
    1430            4 :                         ResidentOrWantedEvicted::WantedEvicted(_, version) => {
    1431            4 :                             // if we were not doing the version check, we would need to try to
    1432            4 :                             // upgrade the weak here to see if it really is dropped. version check
    1433            4 :                             // is done instead assuming that it is cheaper.
    1434            4 :                             tracing::debug!(
    1435              :                                 version,
    1436              :                                 only_version,
    1437            0 :                                 "version mismatch, not deinitializing"
    1438              :                             );
    1439            4 :                             return Err(EvictionCancelled::VersionCheckFailed);
    1440              :                         }
    1441              :                         ResidentOrWantedEvicted::Resident(_) => {
    1442            4 :                             return Err(EvictionCancelled::AlreadyReinitialized);
    1443              :                         }
    1444              :                     }
    1445              :                 }
    1446            4 :                 Err(permit) => {
    1447            4 :                     tracing::debug!("continuing after cancelled get_or_maybe_download or eviction");
    1448            4 :                     (None, permit)
    1449              :                 }
    1450              :             };
    1451              : 
    1452           36 :             permit
    1453           36 :         };
    1454           36 : 
    1455           36 :         let span = tracing::Span::current();
    1456           36 : 
    1457           36 :         let spawned_at = std::time::Instant::now();
    1458           36 : 
    1459           36 :         // this is on purpose a detached spawn; we don't need to wait for it
    1460           36 :         //
    1461           36 :         // eviction completion reporting is the only thing hinging on this, and it can be just as
    1462           36 :         // well from a spawn_blocking thread.
    1463           36 :         //
    1464           36 :         // important to note that now that we've acquired the permit we have made sure the evicted
    1465           36 :         // file is either the exact `WantedEvicted` we wanted to evict, or uninitialized in case
    1466           36 :         // there are multiple evictions. The rest is not cancellable, and we've now commited to
    1467           36 :         // evicting.
    1468           36 :         //
    1469           36 :         // If spawn_blocking has a queue and maximum number of threads are in use, we could stall
    1470           36 :         // reads. We will need to add cancellation for that if necessary.
    1471           36 :         Self::spawn_blocking(move || {
    1472           36 :             let _span = span.entered();
    1473           36 : 
    1474           36 :             let res = self.evict_blocking(&timeline, &gate, &permit);
    1475           36 : 
    1476           36 :             let waiters = self.inner.initializer_count();
    1477           36 : 
    1478           36 :             if waiters > 0 {
    1479            0 :                 LAYER_IMPL_METRICS.inc_evicted_with_waiters();
    1480           36 :             }
    1481              : 
    1482           36 :             let completed_in = spawned_at.elapsed();
    1483           36 :             LAYER_IMPL_METRICS.record_time_to_evict(completed_in);
    1484           36 : 
    1485           36 :             match res {
    1486           36 :                 Ok(()) => LAYER_IMPL_METRICS.inc_completed_evictions(),
    1487            0 :                 Err(e) => LAYER_IMPL_METRICS.inc_eviction_cancelled(e),
    1488              :             }
    1489              : 
    1490           36 :             tracing::debug!(?res, elapsed_ms=%completed_in.as_millis(), %waiters, "eviction completed");
    1491           36 :         });
    1492           36 : 
    1493           36 :         Ok(())
    1494           48 :     }
    1495              : 
    1496              :     /// This is blocking only to do just one spawn_blocking hop compared to multiple via tokio::fs.
    1497           36 :     fn evict_blocking(
    1498           36 :         &self,
    1499           36 :         timeline: &Timeline,
    1500           36 :         _gate: &gate::GateGuard,
    1501           36 :         _permit: &heavier_once_cell::InitPermit,
    1502           36 :     ) -> Result<(), EvictionCancelled> {
    1503           36 :         // now accesses to `self.inner.get_or_init*` wait on the semaphore or the `_permit`
    1504           36 : 
    1505           36 :         match capture_mtime_and_remove(&self.path) {
    1506           36 :             Ok(local_layer_mtime) => {
    1507           36 :                 let duration = SystemTime::now().duration_since(local_layer_mtime);
    1508           36 :                 match duration {
    1509           36 :                     Ok(elapsed) => {
    1510           36 :                         let accessed_and_visible = self.access_stats.accessed()
    1511            8 :                             && self.access_stats.visibility() == LayerVisibilityHint::Visible;
    1512           36 :                         if accessed_and_visible {
    1513            8 :                             // Only layers used for reads contribute to our "low residence" metric that is used
    1514            8 :                             // to detect thrashing.  Layers promoted for other reasons (e.g. compaction) are allowed
    1515            8 :                             // to be rapidly evicted without contributing to this metric.
    1516            8 :                             timeline
    1517            8 :                                 .metrics
    1518            8 :                                 .evictions_with_low_residence_duration
    1519            8 :                                 .read()
    1520            8 :                                 .unwrap()
    1521            8 :                                 .observe(elapsed);
    1522           28 :                         }
    1523              : 
    1524           36 :                         tracing::info!(
    1525            0 :                             residence_millis = elapsed.as_millis(),
    1526            0 :                             accessed_and_visible,
    1527            0 :                             "evicted layer after known residence period"
    1528              :                         );
    1529              :                     }
    1530              :                     Err(_) => {
    1531            0 :                         tracing::info!("evicted layer after unknown residence period");
    1532              :                     }
    1533              :                 }
    1534           36 :                 timeline.metrics.evictions.inc();
    1535           36 :                 timeline
    1536           36 :                     .metrics
    1537           36 :                     .resident_physical_size_sub(self.desc.file_size);
    1538              :             }
    1539            0 :             Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
    1540            0 :                 tracing::error!(
    1541              :                     layer_size = %self.desc.file_size,
    1542            0 :                     "failed to evict layer from disk, it was already gone"
    1543              :                 );
    1544            0 :                 return Err(EvictionCancelled::FileNotFound);
    1545              :             }
    1546            0 :             Err(e) => {
    1547            0 :                 // FIXME: this should probably be an abort
    1548            0 :                 tracing::error!("failed to evict file from disk: {e:#}");
    1549            0 :                 return Err(EvictionCancelled::RemoveFailed);
    1550              :             }
    1551              :         }
    1552              : 
    1553           36 :         self.access_stats.record_residence_event();
    1554           36 : 
    1555           36 :         self.status.as_ref().unwrap().send_replace(Status::Evicted);
    1556           36 : 
    1557           36 :         *self.last_evicted_at.lock().unwrap() = Some(std::time::Instant::now());
    1558           36 : 
    1559           36 :         Ok(())
    1560           36 :     }
    1561              : 
    1562         5724 :     fn metadata(&self) -> LayerFileMetadata {
    1563         5724 :         LayerFileMetadata::new(self.desc.file_size, self.generation, self.shard)
    1564         5724 :     }
    1565              : 
    1566              :     /// Needed to use entered runtime in tests, but otherwise use BACKGROUND_RUNTIME.
    1567              :     ///
    1568              :     /// Synchronizing with spawned tasks is very complicated otherwise.
    1569           60 :     fn spawn<F>(fut: F)
    1570           60 :     where
    1571           60 :         F: std::future::Future<Output = ()> + Send + 'static,
    1572           60 :     {
    1573           60 :         #[cfg(test)]
    1574           60 :         tokio::task::spawn(fut);
    1575           60 :         #[cfg(not(test))]
    1576           60 :         crate::task_mgr::BACKGROUND_RUNTIME.spawn(fut);
    1577           60 :     }
    1578              : 
    1579              :     /// Needed to use entered runtime in tests, but otherwise use BACKGROUND_RUNTIME.
    1580         1060 :     fn spawn_blocking<F>(f: F)
    1581         1060 :     where
    1582         1060 :         F: FnOnce() + Send + 'static,
    1583         1060 :     {
    1584         1060 :         #[cfg(test)]
    1585         1060 :         tokio::task::spawn_blocking(f);
    1586         1060 :         #[cfg(not(test))]
    1587         1060 :         crate::task_mgr::BACKGROUND_RUNTIME.spawn_blocking(f);
    1588         1060 :     }
    1589              : }
    1590              : 
    1591           36 : fn capture_mtime_and_remove(path: &Utf8Path) -> Result<SystemTime, std::io::Error> {
    1592           36 :     let m = path.metadata()?;
    1593           36 :     let local_layer_mtime = m.modified()?;
    1594           36 :     std::fs::remove_file(path)?;
    1595           36 :     Ok(local_layer_mtime)
    1596           36 : }
    1597              : 
    1598              : #[derive(Debug, thiserror::Error)]
    1599              : pub(crate) enum EvictionError {
    1600              :     #[error("layer was already evicted")]
    1601              :     NotFound,
    1602              : 
    1603              :     /// Evictions must always lose to downloads in races, and this time it happened.
    1604              :     #[error("layer was downloaded instead")]
    1605              :     Downloaded,
    1606              : 
    1607              :     #[error("eviction did not happen within timeout")]
    1608              :     Timeout,
    1609              : }
    1610              : 
    1611              : /// Error internal to the [`LayerInner::get_or_maybe_download`]
    1612              : #[derive(Debug, thiserror::Error)]
    1613              : pub(crate) enum DownloadError {
    1614              :     #[error("timeline has already shutdown")]
    1615              :     TimelineShutdown,
    1616              :     #[error("context denies downloading")]
    1617              :     ContextAndConfigReallyDeniesDownloads,
    1618              :     #[error("downloading is really required but not allowed by this method")]
    1619              :     DownloadRequired,
    1620              :     #[error("layer path exists, but it is not a file: {0:?}")]
    1621              :     NotFile(std::fs::FileType),
    1622              :     /// Why no error here? Because it will be reported by page_service. We should had also done
    1623              :     /// retries already.
    1624              :     #[error("downloading evicted layer file failed")]
    1625              :     DownloadFailed,
    1626              :     #[error("downloading failed, possibly for shutdown")]
    1627              :     DownloadCancelled,
    1628              :     #[error("pre-condition: stat before download failed")]
    1629              :     PreStatFailed(#[source] std::io::Error),
    1630              : 
    1631              :     #[cfg(test)]
    1632              :     #[error("failpoint: {0:?}")]
    1633              :     Failpoint(failpoints::FailpointKind),
    1634              : }
    1635              : 
    1636              : impl DownloadError {
    1637            0 :     pub(crate) fn is_cancelled(&self) -> bool {
    1638            0 :         matches!(self, DownloadError::DownloadCancelled)
    1639            0 :     }
    1640              : }
    1641              : 
    1642              : #[derive(Debug, PartialEq)]
    1643              : pub(crate) enum NeedsDownload {
    1644              :     NotFound,
    1645              :     NotFile(std::fs::FileType),
    1646              :     WrongSize { actual: u64, expected: u64 },
    1647              : }
    1648              : 
    1649              : impl std::fmt::Display for NeedsDownload {
    1650           12 :     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
    1651           12 :         match self {
    1652           12 :             NeedsDownload::NotFound => write!(f, "file was not found"),
    1653            0 :             NeedsDownload::NotFile(ft) => write!(f, "path is not a file; {ft:?}"),
    1654            0 :             NeedsDownload::WrongSize { actual, expected } => {
    1655            0 :                 write!(f, "file size mismatch {actual} vs. {expected}")
    1656              :             }
    1657              :         }
    1658           12 :     }
    1659              : }
    1660              : 
    1661              : /// Existence of `DownloadedLayer` means that we have the file locally, and can later evict it.
    1662              : pub(crate) struct DownloadedLayer {
    1663              :     owner: Weak<LayerInner>,
    1664              :     // Use tokio OnceCell as we do not need to deinitialize this, it'll just get dropped with the
    1665              :     // DownloadedLayer
    1666              :     kind: tokio::sync::OnceCell<anyhow::Result<LayerKind>>,
    1667              :     version: usize,
    1668              : }
    1669              : 
    1670              : impl std::fmt::Debug for DownloadedLayer {
    1671            0 :     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
    1672            0 :         f.debug_struct("DownloadedLayer")
    1673            0 :             // owner omitted because it is always "Weak"
    1674            0 :             .field("kind", &self.kind)
    1675            0 :             .field("version", &self.version)
    1676            0 :             .finish()
    1677            0 :     }
    1678              : }
    1679              : 
    1680              : impl Drop for DownloadedLayer {
    1681         1460 :     fn drop(&mut self) {
    1682         1460 :         if let Some(owner) = self.owner.upgrade() {
    1683           48 :             owner.on_downloaded_layer_drop(self.version);
    1684         1412 :         } else {
    1685         1412 :             // Layer::drop will handle cancelling the eviction; because of drop order and
    1686         1412 :             // `DownloadedLayer` never leaking, we cannot know here if eviction was requested.
    1687         1412 :         }
    1688         1460 :     }
    1689              : }
    1690              : 
    1691              : impl DownloadedLayer {
    1692              :     /// Initializes the `DeltaLayerInner` or `ImageLayerInner` within [`LayerKind`].
    1693              :     /// Failure to load the layer is sticky, i.e., future `get()` calls will return
    1694              :     /// the initial load failure immediately.
    1695              :     ///
    1696              :     /// `owner` parameter is a strong reference at the same `LayerInner` as the
    1697              :     /// `DownloadedLayer::owner` would be when upgraded. Given how this method ends up called,
    1698              :     /// we will always have the LayerInner on the callstack, so we can just use it.
    1699       482278 :     async fn get<'a>(
    1700       482278 :         &'a self,
    1701       482278 :         owner: &Arc<LayerInner>,
    1702       482278 :         ctx: &RequestContext,
    1703       482278 :     ) -> anyhow::Result<&'a LayerKind> {
    1704       482278 :         let init = || async {
    1705         2456 :             assert_eq!(
    1706         2456 :                 Weak::as_ptr(&self.owner),
    1707         2456 :                 Arc::as_ptr(owner),
    1708            0 :                 "these are the same, just avoiding the upgrade"
    1709              :             );
    1710              : 
    1711         2456 :             let res = if owner.desc.is_delta {
    1712         2188 :                 let ctx = RequestContextBuilder::extend(ctx)
    1713         2188 :                     .page_content_kind(crate::context::PageContentKind::DeltaLayerSummary)
    1714         2188 :                     .build();
    1715         2188 :                 let summary = Some(delta_layer::Summary::expected(
    1716         2188 :                     owner.desc.tenant_shard_id.tenant_id,
    1717         2188 :                     owner.desc.timeline_id,
    1718         2188 :                     owner.desc.key_range.clone(),
    1719         2188 :                     owner.desc.lsn_range.clone(),
    1720         2188 :                 ));
    1721         2188 :                 delta_layer::DeltaLayerInner::load(
    1722         2188 :                     &owner.path,
    1723         2188 :                     summary,
    1724         2188 :                     Some(owner.conf.max_vectored_read_bytes),
    1725         2188 :                     &ctx,
    1726         2188 :                 )
    1727         2188 :                 .await
    1728         2188 :                 .map(LayerKind::Delta)
    1729              :             } else {
    1730          268 :                 let ctx = RequestContextBuilder::extend(ctx)
    1731          268 :                     .page_content_kind(crate::context::PageContentKind::ImageLayerSummary)
    1732          268 :                     .build();
    1733          268 :                 let lsn = owner.desc.image_layer_lsn();
    1734          268 :                 let summary = Some(image_layer::Summary::expected(
    1735          268 :                     owner.desc.tenant_shard_id.tenant_id,
    1736          268 :                     owner.desc.timeline_id,
    1737          268 :                     owner.desc.key_range.clone(),
    1738          268 :                     lsn,
    1739          268 :                 ));
    1740          268 :                 image_layer::ImageLayerInner::load(
    1741          268 :                     &owner.path,
    1742          268 :                     lsn,
    1743          268 :                     summary,
    1744          268 :                     Some(owner.conf.max_vectored_read_bytes),
    1745          268 :                     &ctx,
    1746          268 :                 )
    1747          268 :                 .await
    1748          268 :                 .map(LayerKind::Image)
    1749              :             };
    1750              : 
    1751         2456 :             match res {
    1752         2456 :                 Ok(layer) => Ok(layer),
    1753            0 :                 Err(err) => {
    1754            0 :                     LAYER_IMPL_METRICS.inc_permanent_loading_failures();
    1755            0 :                     // We log this message once over the lifetime of `Self`
    1756            0 :                     // => Ok and good to log backtrace and path here.
    1757            0 :                     tracing::error!(
    1758            0 :                         "layer load failed, assuming permanent failure: {}: {err:?}",
    1759            0 :                         owner.path
    1760              :                     );
    1761            0 :                     Err(err)
    1762              :                 }
    1763              :             }
    1764         4912 :         };
    1765       482278 :         self.kind
    1766       482278 :             .get_or_init(init)
    1767       482278 :             .await
    1768       482278 :             .as_ref()
    1769       482278 :             // We already logged the full backtrace above, once. Don't repeat that here.
    1770       482278 :             .map_err(|e| anyhow::anyhow!("layer load failed earlier: {e}"))
    1771       482278 :     }
    1772              : 
    1773       480190 :     async fn get_values_reconstruct_data(
    1774       480190 :         &self,
    1775       480190 :         this: ResidentLayer,
    1776       480190 :         keyspace: KeySpace,
    1777       480190 :         lsn_range: Range<Lsn>,
    1778       480190 :         reconstruct_data: &mut ValuesReconstructState,
    1779       480190 :         ctx: &RequestContext,
    1780       480190 :     ) -> Result<(), GetVectoredError> {
    1781              :         use LayerKind::*;
    1782              : 
    1783       480190 :         match self
    1784       480190 :             .get(&this.owner.0, ctx)
    1785       480190 :             .await
    1786       480190 :             .map_err(GetVectoredError::Other)?
    1787              :         {
    1788       435074 :             Delta(d) => {
    1789       435074 :                 d.get_values_reconstruct_data(this, keyspace, lsn_range, reconstruct_data, ctx)
    1790       435074 :                     .await
    1791              :             }
    1792        45116 :             Image(i) => {
    1793        45116 :                 i.get_values_reconstruct_data(this, keyspace, reconstruct_data, ctx)
    1794        45116 :                     .await
    1795              :             }
    1796              :         }
    1797       480190 :     }
    1798              : 
    1799            8 :     async fn dump(&self, owner: &Arc<LayerInner>, ctx: &RequestContext) -> anyhow::Result<()> {
    1800              :         use LayerKind::*;
    1801            8 :         match self.get(owner, ctx).await? {
    1802            8 :             Delta(d) => d.dump(ctx).await?,
    1803            0 :             Image(i) => i.dump(ctx).await?,
    1804              :         }
    1805              : 
    1806            8 :         Ok(())
    1807            8 :     }
    1808              : }
    1809              : 
    1810              : /// Wrapper around an actual layer implementation.
    1811              : #[derive(Debug)]
    1812              : enum LayerKind {
    1813              :     Delta(delta_layer::DeltaLayerInner),
    1814              :     Image(image_layer::ImageLayerInner),
    1815              : }
    1816              : 
    1817              : /// Guard for forcing a layer be resident while it exists.
    1818              : #[derive(Clone)]
    1819              : pub struct ResidentLayer {
    1820              :     owner: Layer,
    1821              :     downloaded: Arc<DownloadedLayer>,
    1822              : }
    1823              : 
    1824              : impl std::fmt::Display for ResidentLayer {
    1825         4260 :     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
    1826         4260 :         write!(f, "{}", self.owner)
    1827         4260 :     }
    1828              : }
    1829              : 
    1830              : impl std::fmt::Debug for ResidentLayer {
    1831            0 :     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
    1832            0 :         write!(f, "{}", self.owner)
    1833            0 :     }
    1834              : }
    1835              : 
    1836              : impl ResidentLayer {
    1837              :     /// Release the eviction guard, converting back into a plain [`Layer`].
    1838              :     ///
    1839              :     /// You can access the [`Layer`] also by using `as_ref`.
    1840          840 :     pub(crate) fn drop_eviction_guard(self) -> Layer {
    1841          840 :         self.into()
    1842          840 :     }
    1843              : 
    1844              :     /// Loads all keys stored in the layer. Returns key, lsn and value size.
    1845            0 :     #[tracing::instrument(level = tracing::Level::DEBUG, skip_all, fields(layer=%self))]
    1846              :     pub(crate) async fn load_keys<'a>(
    1847              :         &'a self,
    1848              :         ctx: &RequestContext,
    1849              :     ) -> anyhow::Result<Vec<pageserver_api::key::Key>> {
    1850              :         use LayerKind::*;
    1851              : 
    1852              :         let owner = &self.owner.0;
    1853              :         let inner = self.downloaded.get(owner, ctx).await?;
    1854              : 
    1855              :         // this is valid because the DownloadedLayer::kind is a OnceCell, not a
    1856              :         // Mutex<OnceCell>, so we cannot go and deinitialize the value with OnceCell::take
    1857              :         // while it's being held.
    1858              :         self.owner.record_access(ctx);
    1859              : 
    1860              :         let res = match inner {
    1861              :             Delta(ref d) => delta_layer::DeltaLayerInner::load_keys(d, ctx).await,
    1862              :             Image(ref i) => image_layer::ImageLayerInner::load_keys(i, ctx).await,
    1863              :         };
    1864            0 :         res.with_context(|| format!("Layer index is corrupted for {self}"))
    1865              :     }
    1866              : 
    1867              :     /// Read all they keys in this layer which match the ShardIdentity, and write them all to
    1868              :     /// the provided writer.  Return the number of keys written.
    1869           16 :     #[tracing::instrument(level = tracing::Level::DEBUG, skip_all, fields(layer=%self))]
    1870              :     pub(crate) async fn filter(
    1871              :         &self,
    1872              :         shard_identity: &ShardIdentity,
    1873              :         writer: &mut ImageLayerWriter,
    1874              :         ctx: &RequestContext,
    1875              :     ) -> Result<usize, CompactionError> {
    1876              :         use LayerKind::*;
    1877              : 
    1878              :         match self
    1879              :             .downloaded
    1880              :             .get(&self.owner.0, ctx)
    1881              :             .await
    1882              :             .map_err(CompactionError::Other)?
    1883              :         {
    1884              :             Delta(_) => {
    1885              :                 return Err(CompactionError::Other(anyhow::anyhow!(format!(
    1886              :                     "cannot filter() on a delta layer {self}"
    1887              :                 ))));
    1888              :             }
    1889              :             Image(i) => i
    1890              :                 .filter(shard_identity, writer, ctx)
    1891              :                 .await
    1892              :                 .map_err(CompactionError::Other),
    1893              :         }
    1894              :     }
    1895              : 
    1896              :     /// Returns the amount of keys and values written to the writer.
    1897           20 :     pub(crate) async fn copy_delta_prefix(
    1898           20 :         &self,
    1899           20 :         writer: &mut super::delta_layer::DeltaLayerWriter,
    1900           20 :         until: Lsn,
    1901           20 :         ctx: &RequestContext,
    1902           20 :     ) -> anyhow::Result<usize> {
    1903              :         use LayerKind::*;
    1904              : 
    1905           20 :         let owner = &self.owner.0;
    1906           20 : 
    1907           20 :         match self.downloaded.get(owner, ctx).await? {
    1908           20 :             Delta(ref d) => d
    1909           20 :                 .copy_prefix(writer, until, ctx)
    1910           20 :                 .await
    1911           20 :                 .with_context(|| format!("copy_delta_prefix until {until} of {self}")),
    1912            0 :             Image(_) => anyhow::bail!(format!("cannot copy_lsn_prefix of image layer {self}")),
    1913              :         }
    1914           20 :     }
    1915              : 
    1916         4105 :     pub(crate) fn local_path(&self) -> &Utf8Path {
    1917         4105 :         &self.owner.0.path
    1918         4105 :     }
    1919              : 
    1920         3876 :     pub(crate) fn metadata(&self) -> LayerFileMetadata {
    1921         3876 :         self.owner.metadata()
    1922         3876 :     }
    1923              : 
    1924              :     /// Cast the layer to a delta, return an error if it is an image layer.
    1925         1908 :     pub(crate) async fn get_as_delta(
    1926         1908 :         &self,
    1927         1908 :         ctx: &RequestContext,
    1928         1908 :     ) -> anyhow::Result<&delta_layer::DeltaLayerInner> {
    1929              :         use LayerKind::*;
    1930         1908 :         match self.downloaded.get(&self.owner.0, ctx).await? {
    1931         1908 :             Delta(ref d) => Ok(d),
    1932            0 :             Image(_) => Err(anyhow::anyhow!("image layer")),
    1933              :         }
    1934         1908 :     }
    1935              : 
    1936              :     /// Cast the layer to an image, return an error if it is a delta layer.
    1937          136 :     pub(crate) async fn get_as_image(
    1938          136 :         &self,
    1939          136 :         ctx: &RequestContext,
    1940          136 :     ) -> anyhow::Result<&image_layer::ImageLayerInner> {
    1941              :         use LayerKind::*;
    1942          136 :         match self.downloaded.get(&self.owner.0, ctx).await? {
    1943          136 :             Image(ref d) => Ok(d),
    1944            0 :             Delta(_) => Err(anyhow::anyhow!("delta layer")),
    1945              :         }
    1946          136 :     }
    1947              : }
    1948              : 
    1949              : impl AsLayerDesc for ResidentLayer {
    1950      2382061 :     fn layer_desc(&self) -> &PersistentLayerDesc {
    1951      2382061 :         self.owner.layer_desc()
    1952      2382061 :     }
    1953              : }
    1954              : 
    1955              : impl AsRef<Layer> for ResidentLayer {
    1956         4056 :     fn as_ref(&self) -> &Layer {
    1957         4056 :         &self.owner
    1958         4056 :     }
    1959              : }
    1960              : 
    1961              : /// Drop the eviction guard.
    1962              : impl From<ResidentLayer> for Layer {
    1963          840 :     fn from(value: ResidentLayer) -> Self {
    1964          840 :         value.owner
    1965          840 :     }
    1966              : }
    1967              : 
    1968              : use metrics::IntCounter;
    1969              : 
    1970              : pub(crate) struct LayerImplMetrics {
    1971              :     started_evictions: IntCounter,
    1972              :     completed_evictions: IntCounter,
    1973              :     cancelled_evictions: enum_map::EnumMap<EvictionCancelled, IntCounter>,
    1974              : 
    1975              :     started_deletes: IntCounter,
    1976              :     completed_deletes: IntCounter,
    1977              :     failed_deletes: enum_map::EnumMap<DeleteFailed, IntCounter>,
    1978              : 
    1979              :     rare_counters: enum_map::EnumMap<RareEvent, IntCounter>,
    1980              :     inits_cancelled: metrics::core::GenericCounter<metrics::core::AtomicU64>,
    1981              :     redownload_after: metrics::Histogram,
    1982              :     time_to_evict: metrics::Histogram,
    1983              : }
    1984              : 
    1985              : impl Default for LayerImplMetrics {
    1986          100 :     fn default() -> Self {
    1987              :         use enum_map::Enum;
    1988              : 
    1989              :         // reminder: these will be pageserver_layer_* with "_total" suffix
    1990              : 
    1991          100 :         let started_evictions = metrics::register_int_counter!(
    1992          100 :             "pageserver_layer_started_evictions",
    1993          100 :             "Evictions started in the Layer implementation"
    1994          100 :         )
    1995          100 :         .unwrap();
    1996          100 :         let completed_evictions = metrics::register_int_counter!(
    1997          100 :             "pageserver_layer_completed_evictions",
    1998          100 :             "Evictions completed in the Layer implementation"
    1999          100 :         )
    2000          100 :         .unwrap();
    2001          100 : 
    2002          100 :         let cancelled_evictions = metrics::register_int_counter_vec!(
    2003          100 :             "pageserver_layer_cancelled_evictions_count",
    2004          100 :             "Different reasons for evictions to have been cancelled or failed",
    2005          100 :             &["reason"]
    2006          100 :         )
    2007          100 :         .unwrap();
    2008          100 : 
    2009          900 :         let cancelled_evictions = enum_map::EnumMap::from_array(std::array::from_fn(|i| {
    2010          900 :             let reason = EvictionCancelled::from_usize(i);
    2011          900 :             let s = reason.as_str();
    2012          900 :             cancelled_evictions.with_label_values(&[s])
    2013          900 :         }));
    2014          100 : 
    2015          100 :         let started_deletes = metrics::register_int_counter!(
    2016          100 :             "pageserver_layer_started_deletes",
    2017          100 :             "Deletions on drop pending in the Layer implementation"
    2018          100 :         )
    2019          100 :         .unwrap();
    2020          100 :         let completed_deletes = metrics::register_int_counter!(
    2021          100 :             "pageserver_layer_completed_deletes",
    2022          100 :             "Deletions on drop completed in the Layer implementation"
    2023          100 :         )
    2024          100 :         .unwrap();
    2025          100 : 
    2026          100 :         let failed_deletes = metrics::register_int_counter_vec!(
    2027          100 :             "pageserver_layer_failed_deletes_count",
    2028          100 :             "Different reasons for deletions on drop to have failed",
    2029          100 :             &["reason"]
    2030          100 :         )
    2031          100 :         .unwrap();
    2032          100 : 
    2033          200 :         let failed_deletes = enum_map::EnumMap::from_array(std::array::from_fn(|i| {
    2034          200 :             let reason = DeleteFailed::from_usize(i);
    2035          200 :             let s = reason.as_str();
    2036          200 :             failed_deletes.with_label_values(&[s])
    2037          200 :         }));
    2038          100 : 
    2039          100 :         let rare_counters = metrics::register_int_counter_vec!(
    2040          100 :             "pageserver_layer_assumed_rare_count",
    2041          100 :             "Times unexpected or assumed rare event happened",
    2042          100 :             &["event"]
    2043          100 :         )
    2044          100 :         .unwrap();
    2045          100 : 
    2046          700 :         let rare_counters = enum_map::EnumMap::from_array(std::array::from_fn(|i| {
    2047          700 :             let event = RareEvent::from_usize(i);
    2048          700 :             let s = event.as_str();
    2049          700 :             rare_counters.with_label_values(&[s])
    2050          700 :         }));
    2051          100 : 
    2052          100 :         let inits_cancelled = metrics::register_int_counter!(
    2053          100 :             "pageserver_layer_inits_cancelled_count",
    2054          100 :             "Times Layer initialization was cancelled",
    2055          100 :         )
    2056          100 :         .unwrap();
    2057          100 : 
    2058          100 :         let redownload_after = {
    2059          100 :             let minute = 60.0;
    2060          100 :             let hour = 60.0 * minute;
    2061          100 :             metrics::register_histogram!(
    2062          100 :                 "pageserver_layer_redownloaded_after",
    2063          100 :                 "Time between evicting and re-downloading.",
    2064          100 :                 vec![
    2065          100 :                     10.0,
    2066          100 :                     30.0,
    2067          100 :                     minute,
    2068          100 :                     5.0 * minute,
    2069          100 :                     15.0 * minute,
    2070          100 :                     30.0 * minute,
    2071          100 :                     hour,
    2072          100 :                     12.0 * hour,
    2073          100 :                 ]
    2074          100 :             )
    2075          100 :             .unwrap()
    2076          100 :         };
    2077          100 : 
    2078          100 :         let time_to_evict = metrics::register_histogram!(
    2079          100 :             "pageserver_layer_eviction_held_permit_seconds",
    2080          100 :             "Time eviction held the permit.",
    2081          100 :             vec![0.001, 0.010, 0.100, 0.500, 1.000, 5.000]
    2082          100 :         )
    2083          100 :         .unwrap();
    2084          100 : 
    2085          100 :         Self {
    2086          100 :             started_evictions,
    2087          100 :             completed_evictions,
    2088          100 :             cancelled_evictions,
    2089          100 : 
    2090          100 :             started_deletes,
    2091          100 :             completed_deletes,
    2092          100 :             failed_deletes,
    2093          100 : 
    2094          100 :             rare_counters,
    2095          100 :             inits_cancelled,
    2096          100 :             redownload_after,
    2097          100 :             time_to_evict,
    2098          100 :         }
    2099          100 :     }
    2100              : }
    2101              : 
    2102              : impl LayerImplMetrics {
    2103           52 :     fn inc_started_evictions(&self) {
    2104           52 :         self.started_evictions.inc();
    2105           52 :     }
    2106           36 :     fn inc_completed_evictions(&self) {
    2107           36 :         self.completed_evictions.inc();
    2108           36 :     }
    2109           16 :     fn inc_eviction_cancelled(&self, reason: EvictionCancelled) {
    2110           16 :         self.cancelled_evictions[reason].inc()
    2111           16 :     }
    2112              : 
    2113         1032 :     fn inc_started_deletes(&self) {
    2114         1032 :         self.started_deletes.inc();
    2115         1032 :     }
    2116         1020 :     fn inc_completed_deletes(&self) {
    2117         1020 :         self.completed_deletes.inc();
    2118         1020 :     }
    2119            0 :     fn inc_deletes_failed(&self, reason: DeleteFailed) {
    2120            0 :         self.failed_deletes[reason].inc();
    2121            0 :     }
    2122              : 
    2123              :     /// Counted separatedly from failed layer deletes because we will complete the layer deletion
    2124              :     /// attempt regardless of failure to delete local file.
    2125            0 :     fn inc_delete_removes_failed(&self) {
    2126            0 :         self.rare_counters[RareEvent::RemoveOnDropFailed].inc();
    2127            0 :     }
    2128              : 
    2129              :     /// Expected rare just as cancellations are rare, but we could have cancellations separate from
    2130              :     /// the single caller which can start the download, so use this counter to separte them.
    2131            0 :     fn inc_init_completed_without_requester(&self) {
    2132            0 :         self.rare_counters[RareEvent::InitCompletedWithoutRequester].inc();
    2133            0 :     }
    2134              : 
    2135              :     /// Expected rare because cancellations are unexpected, and failures are unexpected
    2136            0 :     fn inc_download_failed_without_requester(&self) {
    2137            0 :         self.rare_counters[RareEvent::DownloadFailedWithoutRequester].inc();
    2138            0 :     }
    2139              : 
    2140              :     /// The Weak in ResidentOrWantedEvicted::WantedEvicted was successfully upgraded.
    2141              :     ///
    2142              :     /// If this counter is always zero, we should replace ResidentOrWantedEvicted type with an
    2143              :     /// Option.
    2144            0 :     fn inc_raced_wanted_evicted_accesses(&self) {
    2145            0 :         self.rare_counters[RareEvent::UpgradedWantedEvicted].inc();
    2146            0 :     }
    2147              : 
    2148              :     /// These are only expected for [`Self::inc_init_cancelled`] amount when
    2149              :     /// running with remote storage.
    2150           12 :     fn inc_init_needed_no_download(&self) {
    2151           12 :         self.rare_counters[RareEvent::InitWithoutDownload].inc();
    2152           12 :     }
    2153              : 
    2154              :     /// Expected rare because all layer files should be readable and good
    2155            0 :     fn inc_permanent_loading_failures(&self) {
    2156            0 :         self.rare_counters[RareEvent::PermanentLoadingFailure].inc();
    2157            0 :     }
    2158              : 
    2159            0 :     fn inc_init_cancelled(&self) {
    2160            0 :         self.inits_cancelled.inc()
    2161            0 :     }
    2162              : 
    2163           12 :     fn record_redownloaded_after(&self, duration: std::time::Duration) {
    2164           12 :         self.redownload_after.observe(duration.as_secs_f64())
    2165           12 :     }
    2166              : 
    2167              :     /// This would be bad if it ever happened, or mean extreme disk pressure. We should probably
    2168              :     /// instead cancel eviction if we would have read waiters. We cannot however separate reads
    2169              :     /// from other evictions, so this could have noise as well.
    2170            0 :     fn inc_evicted_with_waiters(&self) {
    2171            0 :         self.rare_counters[RareEvent::EvictedWithWaiters].inc();
    2172            0 :     }
    2173              : 
    2174              :     /// Recorded at least initially as the permit is now acquired in async context before
    2175              :     /// spawn_blocking action.
    2176           36 :     fn record_time_to_evict(&self, duration: std::time::Duration) {
    2177           36 :         self.time_to_evict.observe(duration.as_secs_f64())
    2178           36 :     }
    2179              : }
    2180              : 
    2181              : #[derive(Debug, Clone, Copy, enum_map::Enum)]
    2182              : enum EvictionCancelled {
    2183              :     LayerGone,
    2184              :     TimelineGone,
    2185              :     VersionCheckFailed,
    2186              :     FileNotFound,
    2187              :     RemoveFailed,
    2188              :     AlreadyReinitialized,
    2189              :     /// Not evicted because of a pending reinitialization
    2190              :     LostToDownload,
    2191              :     /// After eviction, there was a new layer access which cancelled the eviction.
    2192              :     UpgradedBackOnAccess,
    2193              :     UnexpectedEvictedState,
    2194              : }
    2195              : 
    2196              : impl EvictionCancelled {
    2197          900 :     fn as_str(&self) -> &'static str {
    2198          900 :         match self {
    2199          100 :             EvictionCancelled::LayerGone => "layer_gone",
    2200          100 :             EvictionCancelled::TimelineGone => "timeline_gone",
    2201          100 :             EvictionCancelled::VersionCheckFailed => "version_check_fail",
    2202          100 :             EvictionCancelled::FileNotFound => "file_not_found",
    2203          100 :             EvictionCancelled::RemoveFailed => "remove_failed",
    2204          100 :             EvictionCancelled::AlreadyReinitialized => "already_reinitialized",
    2205          100 :             EvictionCancelled::LostToDownload => "lost_to_download",
    2206          100 :             EvictionCancelled::UpgradedBackOnAccess => "upgraded_back_on_access",
    2207          100 :             EvictionCancelled::UnexpectedEvictedState => "unexpected_evicted_state",
    2208              :         }
    2209          900 :     }
    2210              : }
    2211              : 
    2212              : #[derive(enum_map::Enum)]
    2213              : enum DeleteFailed {
    2214              :     TimelineGone,
    2215              :     DeleteSchedulingFailed,
    2216              : }
    2217              : 
    2218              : impl DeleteFailed {
    2219          200 :     fn as_str(&self) -> &'static str {
    2220          200 :         match self {
    2221          100 :             DeleteFailed::TimelineGone => "timeline_gone",
    2222          100 :             DeleteFailed::DeleteSchedulingFailed => "delete_scheduling_failed",
    2223              :         }
    2224          200 :     }
    2225              : }
    2226              : 
    2227              : #[derive(enum_map::Enum)]
    2228              : enum RareEvent {
    2229              :     RemoveOnDropFailed,
    2230              :     InitCompletedWithoutRequester,
    2231              :     DownloadFailedWithoutRequester,
    2232              :     UpgradedWantedEvicted,
    2233              :     InitWithoutDownload,
    2234              :     PermanentLoadingFailure,
    2235              :     EvictedWithWaiters,
    2236              : }
    2237              : 
    2238              : impl RareEvent {
    2239          700 :     fn as_str(&self) -> &'static str {
    2240              :         use RareEvent::*;
    2241              : 
    2242          700 :         match self {
    2243          100 :             RemoveOnDropFailed => "remove_on_drop_failed",
    2244          100 :             InitCompletedWithoutRequester => "init_completed_without",
    2245          100 :             DownloadFailedWithoutRequester => "download_failed_without",
    2246          100 :             UpgradedWantedEvicted => "raced_wanted_evicted",
    2247          100 :             InitWithoutDownload => "init_needed_no_download",
    2248          100 :             PermanentLoadingFailure => "permanent_loading_failure",
    2249          100 :             EvictedWithWaiters => "evicted_with_waiters",
    2250              :         }
    2251          700 :     }
    2252              : }
    2253              : 
    2254              : pub(crate) static LAYER_IMPL_METRICS: once_cell::sync::Lazy<LayerImplMetrics> =
    2255              :     once_cell::sync::Lazy::new(LayerImplMetrics::default);
        

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