LCOV - code coverage report
Current view: top level - pebble - format_major_version.go (source / functions) Coverage Total Hit
Test: 2025-02-09 08:17Z 12f37e44 - tests + meta.lcov Lines: 55.2 % 212 117
Test Date: 2025-02-09 08:18:31 Functions: - 0 0

            Line data    Source code
       1              : // Copyright 2021 The LevelDB-Go and Pebble Authors. All rights reserved. Use
       2              : // of this source code is governed by a BSD-style license that can be found in
       3              : // the LICENSE file.
       4              : 
       5              : package pebble
       6              : 
       7              : import (
       8              :         "fmt"
       9              :         "strconv"
      10              : 
      11              :         "github.com/cockroachdb/errors"
      12              :         "github.com/cockroachdb/pebble/internal/manifest"
      13              :         "github.com/cockroachdb/pebble/sstable"
      14              :         "github.com/cockroachdb/pebble/vfs"
      15              :         "github.com/cockroachdb/pebble/vfs/atomicfs"
      16              : )
      17              : 
      18              : // FormatMajorVersion is a constant controlling the format of persisted
      19              : // data. Backwards incompatible changes to durable formats are gated
      20              : // behind new format major versions.
      21              : //
      22              : // At any point, a database's format major version may be bumped.
      23              : // However, once a database's format major version is increased,
      24              : // previous versions of Pebble will refuse to open the database.
      25              : //
      26              : // The zero value format is the FormatDefault constant. The exact
      27              : // FormatVersion that the default corresponds to may change with time.
      28              : type FormatMajorVersion uint64
      29              : 
      30              : // SafeValue implements redact.SafeValue.
      31            0 : func (v FormatMajorVersion) SafeValue() {}
      32              : 
      33              : // String implements fmt.Stringer.
      34            2 : func (v FormatMajorVersion) String() string {
      35            2 :         // NB: This must not change. It's used as the value for the on-disk
      36            2 :         // version marker file.
      37            2 :         //
      38            2 :         // Specifically, this value must always parse as a base 10 integer
      39            2 :         // that fits in a uint64. We format it as zero-padded, 3-digit
      40            2 :         // number today, but the padding may change.
      41            2 :         return fmt.Sprintf("%03d", v)
      42            2 : }
      43              : 
      44              : const (
      45              :         // FormatDefault leaves the format version unspecified. When used to create a
      46              :         // new store, Pebble will choose the earliest format version it supports.
      47              :         FormatDefault FormatMajorVersion = iota
      48              : 
      49              :         // 21.2 versions.
      50              : 
      51              :         // FormatMostCompatible maintains the most backwards compatibility,
      52              :         // maintaining bi-directional compatibility with RocksDB 6.2.1 in
      53              :         // the particular configuration described in the Pebble README.
      54              :         // Deprecated.
      55              :         _ // FormatMostCompatible
      56              : 
      57              :         // formatVersionedManifestMarker is the first
      58              :         // backwards-incompatible change made to Pebble, introducing the
      59              :         // format-version marker file for handling backwards-incompatible
      60              :         // changes more broadly, and replacing the `CURRENT` file with a
      61              :         // marker file.
      62              :         //
      63              :         // This format version is intended as an intermediary version state.
      64              :         // It is deliberately unexported to discourage direct use of this
      65              :         // format major version.  Clients should use FormatVersioned which
      66              :         // also ensures earlier versions of Pebble fail to open a database
      67              :         // written in a future format major version.
      68              :         // Deprecated.
      69              :         _ // formatVersionedManifestMarker
      70              : 
      71              :         // FormatVersioned is a new format major version that replaces the
      72              :         // old `CURRENT` file with a new 'marker' file scheme.  Previous
      73              :         // Pebble versions will be unable to open the database unless
      74              :         // they're aware of format versions.
      75              :         // Deprecated.
      76              :         _ // FormatVersioned
      77              : 
      78              :         // FormatSetWithDelete is a format major version that introduces a new key
      79              :         // kind, base.InternalKeyKindSetWithDelete. Previous Pebble versions will be
      80              :         // unable to open this database.
      81              :         // Deprecated.
      82              :         _ // FormatSetWithDelete
      83              : 
      84              :         // 22.1 versions.
      85              : 
      86              :         // FormatBlockPropertyCollector is a format major version that introduces
      87              :         // BlockPropertyCollectors.
      88              :         // Deprecated.
      89              :         _ // FormatBlockPropertyCollector
      90              : 
      91              :         // FormatSplitUserKeysMarked is a format major version that guarantees that
      92              :         // all files that share user keys with neighbors are marked for compaction
      93              :         // in the manifest. Ratcheting to FormatSplitUserKeysMarked will block
      94              :         // (without holding mutexes) until the scan of the LSM is complete and the
      95              :         // manifest has been rotated.
      96              :         // Deprecated.
      97              :         _ // FormatSplitUserKeysMarked
      98              : 
      99              :         // 22.2 versions.
     100              : 
     101              :         // FormatSplitUserKeysMarkedCompacted is a format major version that
     102              :         // guarantees that all files explicitly marked for compaction in the manifest
     103              :         // have been compacted. Combined with the FormatSplitUserKeysMarked format
     104              :         // major version, this version guarantees that there are no user keys split
     105              :         // across multiple files within a level L1+. Ratcheting to this format version
     106              :         // will block (without holding mutexes) until all necessary compactions for
     107              :         // files marked for compaction are complete.
     108              :         // Deprecated.
     109              :         _ // FormatSplitUserKeysMarkedCompacted
     110              : 
     111              :         // FormatRangeKeys is a format major version that introduces range keys.
     112              :         // Deprecated.
     113              :         _ // FormatRangeKeys
     114              : 
     115              :         // FormatMinTableFormatPebblev1 is a format major version that guarantees that
     116              :         // tables created by or ingested into the DB at or above this format major
     117              :         // version will have a table format version of at least Pebblev1 (Block
     118              :         // Properties).
     119              :         // Deprecated.
     120              :         _ // FormatMinTableFormatPebblev1
     121              : 
     122              :         // FormatPrePebblev1Marked is a format major version that guarantees that all
     123              :         // sstables with a table format version pre-Pebblev1 (i.e. those that are
     124              :         // guaranteed to not contain block properties) are marked for compaction in
     125              :         // the manifest. Ratcheting to FormatPrePebblev1Marked will block (without
     126              :         // holding mutexes) until the scan of the LSM is complete and the manifest has
     127              :         // been rotated.
     128              :         // Deprecated.
     129              :         _ // FormatPrePebblev1Marked
     130              : 
     131              :         // 23.1 versions.
     132              : 
     133              :         // formatUnusedPrePebblev1MarkedCompacted is an unused format major version.
     134              :         // This format major version was originally intended to ship in the 23.1
     135              :         // release. It was later decided that this should be deferred until a
     136              :         // subsequent release. The original ordering is preserved so as not to
     137              :         // introduce breaking changes in Cockroach.
     138              :         _ // formatUnusedPrePebblev1MarkedCompacted
     139              : 
     140              :         // FormatSSTableValueBlocks is a format major version that adds support for
     141              :         // storing values in value blocks in the sstable. Value block support is not
     142              :         // necessarily enabled when writing sstables, when running with this format
     143              :         // major version.
     144              :         _ // FormatSSTableValueBlocks
     145              : 
     146              :         // FormatFlushableIngest is a format major version that enables lazy
     147              :         // addition of ingested sstables into the LSM structure. When an ingest
     148              :         // overlaps with a memtable, a record of the ingest is written to the WAL
     149              :         // without waiting for a flush. Subsequent reads treat the ingested files as
     150              :         // a level above the overlapping memtable. Once the memtable is flushed, the
     151              :         // ingested files are moved into the lowest possible levels.
     152              :         //
     153              :         // This feature is behind a format major version because it required
     154              :         // breaking changes to the WAL format.
     155              :         FormatFlushableIngest
     156              : 
     157              :         // 23.2 versions.
     158              : 
     159              :         // FormatPrePebblev1MarkedCompacted is a format major version that guarantees
     160              :         // that all sstables explicitly marked for compaction in the manifest (see
     161              :         // FormatPrePebblev1Marked) have been compacted. Ratcheting to this format
     162              :         // version will block (without holding mutexes) until all necessary
     163              :         // compactions for files marked for compaction are complete.
     164              :         FormatPrePebblev1MarkedCompacted
     165              : 
     166              :         // FormatDeleteSizedAndObsolete is a format major version that adds support
     167              :         // for deletion tombstones that encode the size of the value they're
     168              :         // expected to delete. This format major version is required before the
     169              :         // associated key kind may be committed through batch applications or
     170              :         // ingests. It also adds support for keys that are marked obsolete (see
     171              :         // sstable/format.go for details).
     172              :         FormatDeleteSizedAndObsolete
     173              : 
     174              :         // FormatVirtualSSTables is a format major version that adds support for
     175              :         // virtual sstables that can reference a sub-range of keys in an underlying
     176              :         // physical sstable. This information is persisted through new,
     177              :         // backward-incompatible fields in the Manifest, and therefore requires
     178              :         // a format major version.
     179              :         FormatVirtualSSTables
     180              : 
     181              :         // FormatSyntheticPrefixSuffix is a format major version that adds support for
     182              :         // sstables to have their content exposed in a different prefix or suffix of
     183              :         // keyspace than the actual prefix/suffix persisted in the keys in such
     184              :         // sstables. The prefix and suffix replacement information is stored in new
     185              :         // fields in the Manifest and thus requires a format major version.
     186              :         FormatSyntheticPrefixSuffix
     187              : 
     188              :         // FormatFlushableIngestExcises is a format major version that adds support for
     189              :         // having excises unconditionally being written as flushable ingestions. This
     190              :         // is implemented through adding a new key kind that can go in the same batches
     191              :         // as flushable ingested sstables.
     192              :         FormatFlushableIngestExcises
     193              : 
     194              :         // FormatColumnarBlocks is a format major version enabling use of the
     195              :         // TableFormatPebblev5 table format, that encodes sstable data blocks, index
     196              :         // blocks and keyspan blocks by organizing the KVs into columns within the
     197              :         // block.
     198              :         FormatColumnarBlocks
     199              : 
     200              :         // -- Add new versions here --
     201              : 
     202              :         // FormatNewest is the most recent format major version.
     203              :         FormatNewest FormatMajorVersion = iota - 1
     204              : 
     205              :         // Experimental versions, which are excluded by FormatNewest (but can be used
     206              :         // in tests) can be defined here.
     207              : 
     208              :         // -- Add experimental versions here --
     209              : 
     210              :         // internalFormatNewest is the most recent, possibly experimental format major
     211              :         // version.
     212              :         internalFormatNewest FormatMajorVersion = iota - 2
     213              : )
     214              : 
     215              : // FormatMinSupported is the minimum format version that is supported by this
     216              : // Pebble version.
     217              : const FormatMinSupported = FormatFlushableIngest
     218              : 
     219              : // FormatMinForSharedObjects it the minimum format version that supports shared
     220              : // objects (see CreateOnShared option).
     221              : const FormatMinForSharedObjects = FormatVirtualSSTables
     222              : 
     223              : // IsSupported returns true if the version is supported by the current Pebble
     224              : // version.
     225            0 : func (v FormatMajorVersion) IsSupported() bool {
     226            0 :         return v == FormatDefault && v >= FormatMinSupported && v <= internalFormatNewest
     227            0 : }
     228              : 
     229              : // MaxTableFormat returns the maximum sstable.TableFormat that can be used at
     230              : // this FormatMajorVersion.
     231            2 : func (v FormatMajorVersion) MaxTableFormat() sstable.TableFormat {
     232            2 :         switch v {
     233            2 :         case FormatDefault, FormatFlushableIngest, FormatPrePebblev1MarkedCompacted:
     234            2 :                 return sstable.TableFormatPebblev3
     235              :         case FormatDeleteSizedAndObsolete, FormatVirtualSSTables, FormatSyntheticPrefixSuffix,
     236            2 :                 FormatFlushableIngestExcises:
     237            2 :                 return sstable.TableFormatPebblev4
     238            2 :         case FormatColumnarBlocks:
     239            2 :                 return sstable.TableFormatPebblev5
     240            1 :         default:
     241            1 :                 panic(fmt.Sprintf("pebble: unsupported format major version: %s", v))
     242              :         }
     243              : }
     244              : 
     245              : // MinTableFormat returns the minimum sstable.TableFormat that can be used at
     246              : // this FormatMajorVersion.
     247            2 : func (v FormatMajorVersion) MinTableFormat() sstable.TableFormat {
     248            2 :         switch v {
     249              :         case FormatDefault, FormatFlushableIngest, FormatPrePebblev1MarkedCompacted,
     250              :                 FormatDeleteSizedAndObsolete, FormatVirtualSSTables, FormatSyntheticPrefixSuffix,
     251            2 :                 FormatFlushableIngestExcises, FormatColumnarBlocks:
     252            2 :                 return sstable.TableFormatPebblev1
     253            1 :         default:
     254            1 :                 panic(fmt.Sprintf("pebble: unsupported format major version: %s", v))
     255              :         }
     256              : }
     257              : 
     258              : // formatMajorVersionMigrations defines the migrations from one format
     259              : // major version to the next. Each migration is defined as a closure
     260              : // which will be invoked on the database before the new format major
     261              : // version is committed. Migrations must be idempotent. Migrations are
     262              : // invoked with d.mu locked.
     263              : //
     264              : // Each migration is responsible for invoking finalizeFormatVersUpgrade
     265              : // to set the new format major version.  RatchetFormatMajorVersion will
     266              : // panic if a migration returns a nil error but fails to finalize the
     267              : // new format major version.
     268              : var formatMajorVersionMigrations = map[FormatMajorVersion]func(*DB) error{
     269            0 :         FormatFlushableIngest: func(d *DB) error { return nil },
     270            2 :         FormatPrePebblev1MarkedCompacted: func(d *DB) error {
     271            2 :                 // Before finalizing the format major version, rewrite any sstables
     272            2 :                 // still marked for compaction. Note all format major versions
     273            2 :                 // migrations are invoked with DB.mu locked.
     274            2 :                 if err := d.compactMarkedFilesLocked(); err != nil {
     275            0 :                         return err
     276            0 :                 }
     277            2 :                 return d.finalizeFormatVersUpgrade(FormatPrePebblev1MarkedCompacted)
     278              :         },
     279            2 :         FormatDeleteSizedAndObsolete: func(d *DB) error {
     280            2 :                 return d.finalizeFormatVersUpgrade(FormatDeleteSizedAndObsolete)
     281            2 :         },
     282            2 :         FormatVirtualSSTables: func(d *DB) error {
     283            2 :                 return d.finalizeFormatVersUpgrade(FormatVirtualSSTables)
     284            2 :         },
     285            2 :         FormatSyntheticPrefixSuffix: func(d *DB) error {
     286            2 :                 return d.finalizeFormatVersUpgrade(FormatSyntheticPrefixSuffix)
     287            2 :         },
     288            2 :         FormatFlushableIngestExcises: func(d *DB) error {
     289            2 :                 return d.finalizeFormatVersUpgrade(FormatFlushableIngestExcises)
     290            2 :         },
     291            2 :         FormatColumnarBlocks: func(d *DB) error {
     292            2 :                 return d.finalizeFormatVersUpgrade(FormatColumnarBlocks)
     293            2 :         },
     294              : }
     295              : 
     296              : const formatVersionMarkerName = `format-version`
     297              : 
     298              : // lookupFormatMajorVersion retrieves the format version from the format version
     299              : // marker file.
     300              : //
     301              : // If such a file does not exist, returns FormatDefault. Note that this case is
     302              : // only acceptable if we are creating a new store (we no longer support
     303              : // FormatMostCompatible which is the only one with no version marker file).
     304              : func lookupFormatMajorVersion(
     305              :         fs vfs.FS, dirname string, ls []string,
     306            2 : ) (FormatMajorVersion, *atomicfs.Marker, error) {
     307            2 :         m, versString, err := atomicfs.LocateMarkerInListing(fs, dirname, formatVersionMarkerName, ls)
     308            2 :         if err != nil {
     309            1 :                 return 0, nil, err
     310            1 :         }
     311            2 :         if versString == "" {
     312            2 :                 return FormatDefault, m, nil
     313            2 :         }
     314            2 :         v, err := strconv.ParseUint(versString, 10, 64)
     315            2 :         if err != nil {
     316            0 :                 return 0, nil, errors.Wrap(err, "parsing format major version")
     317            0 :         }
     318            2 :         vers := FormatMajorVersion(v)
     319            2 :         if vers == FormatDefault {
     320            0 :                 return 0, nil, errors.Newf("pebble: default format major version should not persisted", vers)
     321            0 :         }
     322            2 :         if vers > internalFormatNewest {
     323            1 :                 return 0, nil, errors.Newf("pebble: database %q written in unknown format major version %d", dirname, vers)
     324            1 :         }
     325            2 :         if vers < FormatMinSupported {
     326            0 :                 return 0, nil, errors.Newf("pebble: database %q written in format major version %d which is no longer supported", dirname, vers)
     327            0 :         }
     328            2 :         return vers, m, nil
     329              : }
     330              : 
     331              : // FormatMajorVersion returns the database's active format major
     332              : // version. The format major version may be higher than the one
     333              : // provided in Options when the database was opened if the existing
     334              : // database was written with a higher format version.
     335            2 : func (d *DB) FormatMajorVersion() FormatMajorVersion {
     336            2 :         return FormatMajorVersion(d.mu.formatVers.vers.Load())
     337            2 : }
     338              : 
     339              : // TableFormat returns the TableFormat that the database is currently using when
     340              : // writing sstables. The table format is determined by the database's format
     341              : // major version, as well as experimental settings like EnableValueBlocks and
     342              : // EnableColumnarBlocks.
     343            2 : func (d *DB) TableFormat() sstable.TableFormat {
     344            2 :         // The table is typically written at the maximum allowable format implied by
     345            2 :         // the current format major version of the DB.
     346            2 :         f := d.FormatMajorVersion().MaxTableFormat()
     347            2 :         switch f {
     348            2 :         case sstable.TableFormatPebblev3:
     349            2 :                 // In format major versions with maximum table formats of Pebblev3,
     350            2 :                 // value blocks were conditional on an experimental setting. In format
     351            2 :                 // major versions with maximum table formats of Pebblev4 and higher,
     352            2 :                 // value blocks are always enabled.
     353            2 :                 if d.opts.Experimental.EnableValueBlocks == nil || !d.opts.Experimental.EnableValueBlocks() {
     354            2 :                         f = sstable.TableFormatPebblev2
     355            2 :                 }
     356            2 :         case sstable.TableFormatPebblev5:
     357            2 :                 if d.opts.Experimental.EnableColumnarBlocks == nil || !d.opts.Experimental.EnableColumnarBlocks() {
     358            1 :                         f = sstable.TableFormatPebblev4
     359            1 :                 }
     360              :         }
     361            2 :         return f
     362              : }
     363              : 
     364              : // RatchetFormatMajorVersion ratchets the opened database's format major
     365              : // version to the provided version. It errors if the provided format
     366              : // major version is below the database's current version. Once a
     367              : // database's format major version is upgraded, previous Pebble versions
     368              : // that do not know of the format version will be unable to open the
     369              : // database.
     370            2 : func (d *DB) RatchetFormatMajorVersion(fmv FormatMajorVersion) error {
     371            2 :         if err := d.closed.Load(); err != nil {
     372            1 :                 panic(err)
     373              :         }
     374              : 
     375            2 :         d.mu.Lock()
     376            2 :         defer d.mu.Unlock()
     377            2 :         return d.ratchetFormatMajorVersionLocked(fmv)
     378              : }
     379              : 
     380            2 : func (d *DB) ratchetFormatMajorVersionLocked(formatVers FormatMajorVersion) error {
     381            2 :         if d.opts.ReadOnly {
     382            0 :                 return ErrReadOnly
     383            0 :         }
     384            2 :         if formatVers > internalFormatNewest {
     385            0 :                 // Guard against accidentally forgetting to update internalFormatNewest.
     386            0 :                 return errors.Errorf("pebble: unknown format version %d", formatVers)
     387            0 :         }
     388            2 :         if currentVers := d.FormatMajorVersion(); currentVers > formatVers {
     389            0 :                 return errors.Newf("pebble: database already at format major version %d; cannot reduce to %d",
     390            0 :                         currentVers, formatVers)
     391            0 :         }
     392            2 :         if d.mu.formatVers.ratcheting {
     393            0 :                 return errors.Newf("pebble: database format major version upgrade is in-progress")
     394            0 :         }
     395            2 :         d.mu.formatVers.ratcheting = true
     396            2 :         defer func() { d.mu.formatVers.ratcheting = false }()
     397              : 
     398            2 :         for nextVers := d.FormatMajorVersion() + 1; nextVers <= formatVers; nextVers++ {
     399            2 :                 if err := formatMajorVersionMigrations[nextVers](d); err != nil {
     400            0 :                         return errors.Wrapf(err, "migrating to version %d", nextVers)
     401            0 :                 }
     402              : 
     403              :                 // NB: The migration is responsible for calling
     404              :                 // finalizeFormatVersUpgrade to finalize the upgrade. This
     405              :                 // structure is necessary because some migrations may need to
     406              :                 // update in-memory state (without ever dropping locks) after
     407              :                 // the upgrade is finalized. Here we assert that the upgrade
     408              :                 // did occur.
     409            2 :                 if d.FormatMajorVersion() != nextVers {
     410            0 :                         d.opts.Logger.Fatalf("pebble: successful migration to format version %d never finalized the upgrade", nextVers)
     411            0 :                 }
     412              :         }
     413            2 :         return nil
     414              : }
     415              : 
     416              : // finalizeFormatVersUpgrade is typically only be called from within a
     417              : // format major version migration.
     418              : //
     419              : // See formatMajorVersionMigrations.
     420            2 : func (d *DB) finalizeFormatVersUpgrade(formatVers FormatMajorVersion) error {
     421            2 :         if err := d.writeFormatVersionMarker(formatVers); err != nil {
     422            0 :                 return err
     423            0 :         }
     424            2 :         d.mu.formatVers.vers.Store(uint64(formatVers))
     425            2 :         d.opts.EventListener.FormatUpgrade(formatVers)
     426            2 :         return nil
     427              : }
     428              : 
     429            2 : func (d *DB) writeFormatVersionMarker(formatVers FormatMajorVersion) error {
     430            2 :         // We use the marker to encode the active format version in the
     431            2 :         // marker filename. Unlike other uses of the atomic marker, there is
     432            2 :         // no file with the filename `formatVers.String()` on the
     433            2 :         // filesystem.
     434            2 :         return d.mu.formatVers.marker.Move(formatVers.String())
     435            2 : }
     436              : 
     437              : // compactMarkedFilesLocked performs a migration that schedules rewrite
     438              : // compactions to compact away any sstables marked for compaction.
     439              : // compactMarkedFilesLocked is run while ratcheting the database's format major
     440              : // version to FormatSplitUserKeysMarkedCompacted.
     441              : //
     442              : // Note that while this method is called with the DB.mu held, and will not
     443              : // return until all marked files have been compacted, the mutex is dropped while
     444              : // waiting for compactions to complete (or for slots to free up).
     445            2 : func (d *DB) compactMarkedFilesLocked() error {
     446            2 :         curr := d.mu.versions.currentVersion()
     447            2 :         for curr.Stats.MarkedForCompaction > 0 {
     448            0 :                 // Attempt to schedule a compaction to rewrite a file marked for
     449            0 :                 // compaction.
     450            0 :                 d.maybeScheduleCompactionPicker(func(picker compactionPicker, env compactionEnv) *pickedCompaction {
     451            0 :                         return picker.pickRewriteCompaction(env)
     452            0 :                 })
     453              : 
     454              :                 // The above attempt might succeed and schedule a rewrite compaction. Or
     455              :                 // there might not be available compaction concurrency to schedule the
     456              :                 // compaction.  Or compaction of the file might have already been in
     457              :                 // progress. In any scenario, wait until there's some change in the
     458              :                 // state of active compactions.
     459              : 
     460              :                 // Before waiting, check that the database hasn't been closed. Trying to
     461              :                 // schedule the compaction may have dropped d.mu while waiting for a
     462              :                 // manifest write to complete. In that dropped interim, the database may
     463              :                 // have been closed.
     464            0 :                 if err := d.closed.Load(); err != nil {
     465            0 :                         return err.(error)
     466            0 :                 }
     467              : 
     468              :                 // Some flush or compaction may have scheduled or completed while we waited
     469              :                 // for the manifest lock in maybeScheduleCompactionPicker. Get the latest
     470              :                 // Version before waiting on a compaction.
     471            0 :                 curr = d.mu.versions.currentVersion()
     472            0 : 
     473            0 :                 // Only wait on compactions if there are files still marked for compaction.
     474            0 :                 // NB: Waiting on this condition variable drops d.mu while blocked.
     475            0 :                 if curr.Stats.MarkedForCompaction > 0 {
     476            0 :                         if d.mu.compact.compactingCount == 0 {
     477            0 :                                 panic("expected a compaction of marked files in progress")
     478              :                         }
     479            0 :                         d.mu.compact.cond.Wait()
     480            0 :                         // Refresh the current version again.
     481            0 :                         curr = d.mu.versions.currentVersion()
     482              :                 }
     483              :         }
     484            2 :         return nil
     485              : }
     486              : 
     487              : // findFilesFunc scans the LSM for files, returning true if at least one
     488              : // file was found. The returned array contains the matched files, if any, per
     489              : // level.
     490              : type findFilesFunc func(v *version) (found bool, files [numLevels][]*fileMetadata, _ error)
     491              : 
     492              : // This method is not used currently, but it will be useful the next time we need
     493              : // to mark files for compaction.
     494              : var _ = (*DB)(nil).markFilesLocked
     495              : 
     496              : // markFilesLocked durably marks the files that match the given findFilesFunc for
     497              : // compaction.
     498            0 : func (d *DB) markFilesLocked(findFn findFilesFunc) error {
     499            0 :         jobID := d.newJobIDLocked()
     500            0 : 
     501            0 :         // Acquire a read state to have a view of the LSM and a guarantee that none
     502            0 :         // of the referenced files will be deleted until we've unreferenced the read
     503            0 :         // state. Some findFilesFuncs may read the files, requiring they not be
     504            0 :         // deleted.
     505            0 :         rs := d.loadReadState()
     506            0 :         var (
     507            0 :                 found bool
     508            0 :                 files [numLevels][]*fileMetadata
     509            0 :                 err   error
     510            0 :         )
     511            0 :         func() {
     512            0 :                 defer rs.unrefLocked()
     513            0 :                 // Note the unusual locking: unlock, defer Lock(). The scan of the files in
     514            0 :                 // the version does not need to block other operations that require the
     515            0 :                 // DB.mu. Drop it for the scan, before re-acquiring it.
     516            0 :                 d.mu.Unlock()
     517            0 :                 defer d.mu.Lock()
     518            0 :                 found, files, err = findFn(rs.current)
     519            0 :         }()
     520            0 :         if err != nil {
     521            0 :                 return err
     522            0 :         }
     523              : 
     524              :         // The database lock has been acquired again by the defer within the above
     525              :         // anonymous function.
     526            0 :         if !found {
     527            0 :                 // Nothing to do.
     528            0 :                 return nil
     529            0 :         }
     530              : 
     531              :         // After scanning, if we found files to mark, we fetch the current state of
     532              :         // the LSM (which may have changed) and set MarkedForCompaction on the files,
     533              :         // and update the version's Stats.MarkedForCompaction count, which are both
     534              :         // protected by d.mu.
     535              : 
     536              :         // Lock the manifest for a coherent view of the LSM. The database lock has
     537              :         // been re-acquired by the defer within the above anonymous function.
     538            0 :         d.mu.versions.logLock()
     539            0 :         vers := d.mu.versions.currentVersion()
     540            0 :         for l, filesToMark := range files {
     541            0 :                 if len(filesToMark) == 0 {
     542            0 :                         continue
     543              :                 }
     544            0 :                 for _, f := range filesToMark {
     545            0 :                         // Ignore files to be marked that have already been compacted or marked.
     546            0 :                         if f.CompactionState == manifest.CompactionStateCompacted ||
     547            0 :                                 f.MarkedForCompaction {
     548            0 :                                 continue
     549              :                         }
     550              :                         // Else, mark the file for compaction in this version.
     551            0 :                         vers.Stats.MarkedForCompaction++
     552            0 :                         f.MarkedForCompaction = true
     553              :                 }
     554              :                 // The compaction picker uses the markedForCompactionAnnotator to
     555              :                 // quickly find files marked for compaction, or to quickly determine
     556              :                 // that there are no such files marked for compaction within a level.
     557              :                 // A b-tree node may be annotated with an annotation recording that
     558              :                 // there are no files marked for compaction within the node's subtree,
     559              :                 // based on the assumption that it's static.
     560              :                 //
     561              :                 // Since we're marking files for compaction, these b-tree nodes'
     562              :                 // annotations will be out of date. Clear the compaction-picking
     563              :                 // annotation, so that it's recomputed the next time the compaction
     564              :                 // picker looks for a file marked for compaction.
     565            0 :                 markedForCompactionAnnotator.InvalidateLevelAnnotation(vers.Levels[l])
     566              :         }
     567              : 
     568              :         // The 'marked-for-compaction' bit is persisted in the MANIFEST file
     569              :         // metadata. We've already modified the in-memory file metadata, but the
     570              :         // manifest hasn't been updated. Force rotation to a new MANIFEST file,
     571              :         // which will write every file metadata to the new manifest file and ensure
     572              :         // that the now marked-for-compaction file metadata are persisted as marked.
     573              :         // NB: This call to logAndApply will unlockthe MANIFEST, which we locked up
     574              :         // above before obtaining `vers`.
     575            0 :         return d.mu.versions.logAndApply(
     576            0 :                 jobID,
     577            0 :                 &manifest.VersionEdit{},
     578            0 :                 map[int]*LevelMetrics{},
     579            0 :                 true, /* forceRotation */
     580            0 :                 func() []compactionInfo { return d.getInProgressCompactionInfoLocked(nil) })
     581              : }
        

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