litestream

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 Go to latest Published: Jul 16, 2021 License: Apache-2.0 Imports: 26 Imported by: 9

README

Litestream GitHub release (latest by date) Status GitHub Docker Pulls test

Litestream is a standalone streaming replication tool for SQLite. It runs as a background process and safely replicates changes incrementally to another file or S3. Litestream only communicates with SQLite through the SQLite API so it will not corrupt your database.

If you need support or have ideas for improving Litestream, please join the Litestream Slack or visit the GitHub Discussions. Please visit the Litestream web site for installation instructions and documentation.

If you find this project interesting, please consider starring the project on GitHub.

Acknowledgements

While the Litestream project does not accept external code patches, many of the most valuable contributions are in the forms of testing, feedback, and documentation. These help harden software and streamline usage for other users.

I want to give special thanks to individuals who invest much of their time and energy into the project to help make it better:

Open-source, not open-contribution

Similar to SQLite, Litestream is open source but closed to code contributions. This keeps the code base free of proprietary or licensed code but it also helps me continue to maintain and build Litestream.

As the author of BoltDB, I found that accepting and maintaining third party patches contributed to my burn out and I eventually archived the project. Writing databases & low-level replication tools involves nuance and simple one line changes can have profound and unexpected changes in correctness and performance. Small contributions typically required hours of my time to properly test and validate them.

I am grateful for community involvement, bug reports, & feature requests. I do not wish to come off as anything but welcoming, however, I've made the decision to keep this project closed to contributions for my own mental health and long term viability of the project.

The documentation repository is MIT licensed and pull requests are welcome there.

Documentation

Index

Constants

View Source 
const (
	DefaultMonitorInterval    = 1 * time.Second
	DefaultCheckpointInterval = 1 * time.Minute
	DefaultMinCheckpointPageN = 1000
	DefaultMaxCheckpointPageN = 10000
)

Default DB settings.

View Source 
const (
	WALHeaderChecksumOffset      = 24
	WALFrameHeaderChecksumOffset = 16
)

SQLite WAL constants

View Source 
const (
	MetaDirSuffix = "-litestream"

	WALDirName    = "wal"
	WALExt        = ".wal"
	WALSegmentExt = ".wal.lz4"
	SnapshotExt   = ".snapshot.lz4"

	GenerationNameLen = 16
)

Naming constants.

View Source 
const (
	CheckpointModePassive  = "PASSIVE"
	CheckpointModeFull     = "FULL"
	CheckpointModeRestart  = "RESTART"
	CheckpointModeTruncate = "TRUNCATE"
)

SQLite checkpoint modes.

View Source 
const (
	// WALHeaderSize is the size of the WAL header, in bytes.
	WALHeaderSize = 32

	// WALFrameHeaderSize is the size of the WAL frame header, in bytes.
	WALFrameHeaderSize = 24
)
View Source 
const (
	DefaultSyncInterval           = 1 * time.Second
	DefaultRetention              = 24 * time.Hour
	DefaultRetentionCheckInterval = 1 * time.Hour
)

Default replica settings.

View Source 
const BusyTimeout = 1 * time.Second

BusyTimeout is the timeout to wait for EBUSY from SQLite.

View Source 
const DefaultRestoreParallelism = 8

DefaultRestoreParallelism is the default parallelism when downloading WAL files.

View Source 
const MaxIndex = 0x7FFFFFFF

MaxIndex is the maximum possible WAL index. If this index is reached then a new generation will be started.

Variables

View Source 
var (
	ErrNoGeneration     = errors.New("no generation available")
	ErrNoSnapshots      = errors.New("no snapshots available")
	ErrChecksumMismatch = errors.New("invalid replica, checksum mismatch")
)

Litestream errors.

View Source 
var (
	// LogWriter is the destination writer for all logging.
	LogWriter = os.Stderr

	// LogFlags are the flags passed to log.New().
	LogFlags = 0
)
View Source 
var Tracef = func(format string, a ...interface{}) {}

Tracef is used for low-level tracing.

Functions

func Checksum 

func Checksum(bo binary.ByteOrder, s0, s1 uint32, b []byte) (uint32, uint32)

Checksum computes a running SQLite checksum over a byte slice.

func ComparePos 

func ComparePos(a, b Pos) (int, error)

ComparePos returns -1 if a is less than b, 1 if a is greater than b, and returns 0 if a and b are equal. Only index & offset are compared. Returns an error if generations are not equal.

func FormatIndex 

func FormatIndex(index int) string

FormatIndex formats an index as an 8-character hex value.

func FormatOffset 

func FormatOffset(offset int64) string

FormatOffset formats an offset as an 8-character hex value.

func IsGenerationName 

func IsGenerationName(s string) bool

IsGenerationName returns true if s is the correct length and is only lowercase hex characters.

func ParseIndex 

func ParseIndex(s string) (int, error)

ParseIndex parses a hex-formatted index into an integer.

func ParseOffset 

func ParseOffset(s string) (int64, error)

ParseOffset parses a hex-formatted offset into an integer.

Types

type DB 

type DB struct {

	// Minimum threshold of WAL size, in pages, before a passive checkpoint.
	// A passive checkpoint will attempt a checkpoint but fail if there are
	// active transactions occurring at the same time.
	MinCheckpointPageN int

	// Maximum threshold of WAL size, in pages, before a forced checkpoint.
	// A forced checkpoint will block new transactions and wait for existing
	// transactions to finish before issuing a checkpoint and resetting the WAL.
	//
	// If zero, no checkpoints are forced. This can cause the WAL to grow
	// unbounded if there are always read transactions occurring.
	MaxCheckpointPageN int

	// Time between automatic checkpoints in the WAL. This is done to allow
	// more fine-grained WAL files so that restores can be performed with
	// better precision.
	CheckpointInterval time.Duration

	// Frequency at which to perform db sync.
	MonitorInterval time.Duration

	// List of replicas for the database.
	// Must be set before calling Open().
	Replicas []*Replica

	Logger *log.Logger
	// contains filtered or unexported fields
}

DB represents a managed instance of a SQLite database in the file system.

func NewDB 

func NewDB(path string) *DB

NewDB returns a new instance of DB for a given path.

func (*DB) CRC64 added in v0.3.0 

func (db *DB) CRC64(ctx context.Context) (uint64, Pos, error)

CRC64 returns a CRC-64 ISO checksum of the database and its current position.

This function obtains a read lock so it prevents syncs from occurring until the operation is complete. The database will still be usable but it will be unable to checkpoint during this time.

If dst is set, the database file is copied to that location before checksum.

func (*DB) CalcRestoreTarget added in v0.3.1 

func (db *DB) CalcRestoreTarget(ctx context.Context, opt RestoreOptions) (*Replica, string, error)

CalcRestoreTarget returns a replica & generation to restore from based on opt criteria.

func (*DB) Checkpoint added in v0.3.0 

func (db *DB) Checkpoint(ctx context.Context, mode string) (err error)

Checkpoint performs a checkpoint on the WAL file.

func (*DB) Close 

func (db *DB) Close() (err error)

Close releases the read lock & closes the database. This method should only be called by tests as it causes the underlying database to be checkpointed.

func (*DB) CurrentGeneration 

func (db *DB) CurrentGeneration() (string, error)

CurrentGeneration returns the name of the generation saved to the "generation" file in the meta data directory. Returns empty string if none exists.

func (*DB) DeleteWALSegments 

func (db *DB) DeleteWALSegments(ctx context.Context, a []Pos) error

DeleteWALSegments deletes WAL segments at the given positions.

func (*DB) DirInfo added in v0.3.5 

func (db *DB) DirInfo() os.FileInfo

DirInfo returns the cached file stats for the parent directory of the database file when it was initialized.

func (*DB) FileInfo added in v0.3.5 

func (db *DB) FileInfo() os.FileInfo

FileInfo returns the cached file stats for the database file when it was initialized.

func (*DB) GenerationNamePath 

func (db *DB) GenerationNamePath() string

GenerationNamePath returns the path of the name of the current generation.

func (*DB) GenerationPath 

func (db *DB) GenerationPath(generation string) string

GenerationPath returns the path of a single generation. Panics if generation is blank.

func (*DB) MetaPath 

func (db *DB) MetaPath() string

MetaPath returns the path to the database metadata.

func (*DB) Notify 

func (db *DB) Notify() <-chan struct{}

Notify returns a channel that closes when the shadow WAL changes.

func (*DB) Open 

func (db *DB) Open() (err error)

Open initializes the background monitoring goroutine.

func (*DB) PageSize 

func (db *DB) PageSize() int

PageSize returns the page size of the underlying database. Only valid after database exists & Init() has successfully run.

func (*DB) Path 

func (db *DB) Path() string

Path returns the path to the database.

func (*DB) Pos added in v0.2.0 

func (db *DB) Pos() Pos

Pos returns the cached position of the database. Returns a zero position if no position has been calculated or if there is no generation.

func (*DB) Replica added in v0.2.0 

func (db *DB) Replica(name string) *Replica

Replica returns a replica by name.

func (*DB) SQLDB added in v0.3.0 

func (db *DB) SQLDB() *sql.DB

SQLDB returns a reference to the underlying sql.DB connection.

func (*DB) ShadowWALDir added in v0.2.0 

func (db *DB) ShadowWALDir(generation string) string

ShadowWALDir returns the path of the shadow wal directory. Panics if generation is blank.

func (*DB) SoftClose 

func (db *DB) SoftClose() (err error)

SoftClose closes everything but the underlying db connection. This method is available because the binary needs to avoid closing the database on exit to prevent autocheckpointing.

func (*DB) Sync 

func (db *DB) Sync(ctx context.Context) (err error)

Sync copies pending data from the WAL to the shadow WAL.

func (*DB) UpdatedAt 

func (db *DB) UpdatedAt() (time.Time, error)

UpdatedAt returns the last modified time of the database or WAL file.

func (*DB) WALPath 

func (db *DB) WALPath() string

WALPath returns the path to the database's WAL file.

func (*DB) WALReader 

func (db *DB) WALReader(ctx context.Context, generation string, index int) (_ io.ReadCloser, err error)

WALReader returns the entire uncompressed WAL file for a given index.

func (*DB) WALSegmentReader 

func (db *DB) WALSegmentReader(ctx context.Context, pos Pos) (io.ReadCloser, error)

WALSegmentReader returns a reader for a section of WAL data at the given position. Returns os.ErrNotExist if no matching index/offset is found.

func (*DB) WALSegments 

func (db *DB) WALSegments(ctx context.Context, generation string) (WALSegmentIterator, error)

WALSegments returns an iterator over all available WAL files for a generation.

type Pos 

type Pos struct {
	Generation string // generation name
	Index      int    // wal file index
	Offset     int64  // offset within wal file
}

Pos is a position in the WAL for a generation.

func (Pos) IsZero 

func (p Pos) IsZero() bool

IsZero returns true if p is the zero value.

func (Pos) String 

func (p Pos) String() string

String returns a string representation.

func (Pos) Truncate added in v0.3.5 

func (p Pos) Truncate() Pos

Truncate returns p with the offset truncated to zero.

type Replica 

type Replica struct {

	// Client used to connect to the remote replica.
	Client ReplicaClient

	// Time between syncs with the shadow WAL.
	SyncInterval time.Duration

	// Frequency to create new snapshots.
	SnapshotInterval time.Duration

	// Time to keep snapshots and related WAL files.
	// Database is snapshotted after interval, if needed, and older WAL files are discarded.
	Retention time.Duration

	// Time between checks for retention.
	RetentionCheckInterval time.Duration

	// Time between validation checks.
	ValidationInterval time.Duration

	// If true, replica monitors database for changes automatically.
	// Set to false if replica is being used synchronously (such as in tests).
	MonitorEnabled bool

	Logger *log.Logger
	// contains filtered or unexported fields
}

Replica connects a database to a replication destination via a ReplicaClient. The replica manages periodic synchronization and maintaining the current replica position.

func NewReplica added in v0.3.5 

func NewReplica(db *DB, name string) *Replica

func (*Replica) CalcRestoreTarget added in v0.3.5 

func (r *Replica) CalcRestoreTarget(ctx context.Context, opt RestoreOptions) (generation string, updatedAt time.Time, err error)

CalcRestoreTarget returns a generation to restore from.

func (*Replica) DB added in v0.3.0 

func (r *Replica) DB() *DB

DB returns a reference to the database the replica is attached to, if any.

func (*Replica) EnforceRetention added in v0.3.5 

func (r *Replica) EnforceRetention(ctx context.Context) (err error)

EnforceRetention forces a new snapshot once the retention interval has passed. Older snapshots and WAL files are then removed.

func (*Replica) GenerationCreatedAt added in v0.3.5 

func (r *Replica) GenerationCreatedAt(ctx context.Context, generation string) (time.Time, error)

GenerationCreatedAt returns the earliest creation time of any snapshot. Returns zero time if no snapshots exist.

func (*Replica) GenerationTimeBounds added in v0.3.5 

func (r *Replica) GenerationTimeBounds(ctx context.Context, generation string) (createdAt, updatedAt time.Time, err error)

GenerationTimeBounds returns the creation time & last updated time of a generation. Returns zero time if no snapshots or WAL segments exist.

func (*Replica) Name 

func (r *Replica) Name() string

Name returns the name of the replica.

func (*Replica) Pos added in v0.3.5 

func (r *Replica) Pos() Pos

Pos returns the current replicated position. Returns a zero value if the current position cannot be determined.

func (*Replica) Restore added in v0.3.5 

func (r *Replica) Restore(ctx context.Context, opt RestoreOptions) (err error)

Replica restores the database from a replica based on the options given. This method will restore into opt.OutputPath, if specified, or into the DB's original database path. It can optionally restore from a specific replica or generation or it will automatically choose the best one. Finally, a timestamp can be specified to restore the database to a specific point-in-time.

func (*Replica) Snapshot added in v0.3.5 

func (r *Replica) Snapshot(ctx context.Context) (info SnapshotInfo, err error)

Snapshot copies the entire database to the replica path.

func (*Replica) SnapshotIndexAt 

func (r *Replica) SnapshotIndexAt(ctx context.Context, generation string, timestamp time.Time) (int, error)

SnapshotIndexAt returns the highest index for a snapshot within a generation that occurs before timestamp. If timestamp is zero, returns the latest snapshot.

func (*Replica) SnapshotIndexByIndex added in v0.3.5 

func (r *Replica) SnapshotIndexByIndex(ctx context.Context, generation string, index int) (int, error)

SnapshotIndexbyIndex returns the highest index for a snapshot within a generation that occurs before a given index. If index is MaxInt32, returns the latest snapshot.

func (*Replica) Snapshots added in v0.2.0 

func (r *Replica) Snapshots(ctx context.Context) ([]SnapshotInfo, error)

Snapshots returns a list of all snapshots across all generations.

func (*Replica) Start 

func (r *Replica) Start(ctx context.Context) error

Starts replicating in a background goroutine.

func (*Replica) Stop 

func (r *Replica) Stop(hard bool) (err error)

Stop cancels any outstanding replication and blocks until finished.

Performing a hard stop will close the DB file descriptor which could release locks on per-process locks. Hard stops should only be performed when stopping the entire process.

func (*Replica) Sync added in v0.3.4 

func (r *Replica) Sync(ctx context.Context) (err error)

Sync copies new WAL frames from the shadow WAL to the replica client.

func (*Replica) Validate added in v0.3.5 

func (r *Replica) Validate(ctx context.Context) error

Validate restores the most recent data from a replica and validates that the resulting database matches the current database.

type ReplicaClient added in v0.3.5 

type ReplicaClient interface {
	// Returns the type of client.
	Type() string

	// Returns a list of available generations.
	Generations(ctx context.Context) ([]string, error)

	// Deletes all snapshots & WAL segments within a generation.
	DeleteGeneration(ctx context.Context, generation string) error

	// Returns an iterator of all snapshots within a generation on the replica.
	Snapshots(ctx context.Context, generation string) (SnapshotIterator, error)

	// Writes LZ4 compressed snapshot data to the replica at a given index
	// within a generation. Returns metadata for the snapshot.
	WriteSnapshot(ctx context.Context, generation string, index int, r io.Reader) (SnapshotInfo, error)

	// Deletes a snapshot with the given generation & index.
	DeleteSnapshot(ctx context.Context, generation string, index int) error

	// Returns a reader that contains LZ4 compressed snapshot data for a
	// given index within a generation. Returns an os.ErrNotFound error if
	// the snapshot does not exist.
	SnapshotReader(ctx context.Context, generation string, index int) (io.ReadCloser, error)

	// Returns an iterator of all WAL segments within a generation on the replica.
	WALSegments(ctx context.Context, generation string) (WALSegmentIterator, error)

	// Writes an LZ4 compressed WAL segment at a given position.
	// Returns metadata for the written segment.
	WriteWALSegment(ctx context.Context, pos Pos, r io.Reader) (WALSegmentInfo, error)

	// Deletes one or more WAL segments at the given positions.
	DeleteWALSegments(ctx context.Context, a []Pos) error

	// Returns a reader that contains an LZ4 compressed WAL segment at a given
	// index/offset within a generation. Returns an os.ErrNotFound error if the
	// WAL segment does not exist.
	WALSegmentReader(ctx context.Context, pos Pos) (io.ReadCloser, error)
}

ReplicaClient represents client to connect to a Replica.

type RestoreOptions 

type RestoreOptions struct {
	// Target path to restore into.
	// If blank, the original DB path is used.
	OutputPath string

	// Specific replica to restore from.
	// If blank, all replicas are considered.
	ReplicaName string

	// Specific generation to restore from.
	// If blank, all generations considered.
	Generation string

	// Specific index to restore from.
	// Set to math.MaxInt32 to ignore index.
	Index int

	// Point-in-time to restore database.
	// If zero, database restore to most recent state available.
	Timestamp time.Time

	// Specifies how many WAL files are downloaded in parallel during restore.
	Parallelism int

	// Logging settings.
	Logger  *log.Logger
	Verbose bool
}

RestoreOptions represents options for DB.Restore().

func NewRestoreOptions added in v0.2.0 

func NewRestoreOptions() RestoreOptions

NewRestoreOptions returns a new instance of RestoreOptions with defaults.

type SnapshotInfo added in v0.2.0 

type SnapshotInfo struct {
	Generation string
	Index      int
	Size       int64
	CreatedAt  time.Time
}

SnapshotInfo represents file information about a snapshot.

func FilterSnapshotsAfter added in v0.3.0 

func FilterSnapshotsAfter(a []SnapshotInfo, t time.Time) []SnapshotInfo

FilterSnapshotsAfter returns all snapshots that were created on or after t.

func FindMinSnapshotByGeneration added in v0.3.0 

func FindMinSnapshotByGeneration(a []SnapshotInfo, generation string) *SnapshotInfo

FindMinSnapshotByGeneration finds the snapshot with the lowest index in a generation.

func SliceSnapshotIterator added in v0.3.5 

func SliceSnapshotIterator(itr SnapshotIterator) ([]SnapshotInfo, error)

SliceSnapshotIterator returns all snapshots from an iterator as a slice.

func (*SnapshotInfo) Pos added in v0.3.5 

func (info *SnapshotInfo) Pos() Pos

Pos returns the WAL position when the snapshot was made.

type SnapshotInfoSlice added in v0.3.5 

type SnapshotInfoSlice []SnapshotInfo

SnapshotInfoSlice represents a slice of snapshot metadata.

func (SnapshotInfoSlice) Len added in v0.3.5 

func (a SnapshotInfoSlice) Len() int

func (SnapshotInfoSlice) Less added in v0.3.5 

func (a SnapshotInfoSlice) Less(i, j int) bool

func (SnapshotInfoSlice) Swap added in v0.3.5 

func (a SnapshotInfoSlice) Swap(i, j int)

type SnapshotInfoSliceIterator added in v0.3.5 

type SnapshotInfoSliceIterator struct {
	// contains filtered or unexported fields
}

SnapshotInfoSliceIterator represents an iterator for iterating over a slice of snapshots.

func NewSnapshotInfoSliceIterator added in v0.3.5 

func NewSnapshotInfoSliceIterator(a []SnapshotInfo) *SnapshotInfoSliceIterator

NewSnapshotInfoSliceIterator returns a new instance of SnapshotInfoSliceIterator.

func (*SnapshotInfoSliceIterator) Close added in v0.3.5 

func (itr *SnapshotInfoSliceIterator) Close() error

Close always returns nil.

func (*SnapshotInfoSliceIterator) Err added in v0.3.5 

func (itr *SnapshotInfoSliceIterator) Err() error

Err always returns nil.

func (*SnapshotInfoSliceIterator) Next added in v0.3.5 

func (itr *SnapshotInfoSliceIterator) Next() bool

Next moves to the next snapshot. Returns true if another snapshot is available.

func (*SnapshotInfoSliceIterator) Snapshot added in v0.3.5 

func (itr *SnapshotInfoSliceIterator) Snapshot() SnapshotInfo

Snapshot returns the metadata from the currently positioned snapshot.

type SnapshotIterator added in v0.3.5 

type SnapshotIterator interface {
	io.Closer

	// Prepares the the next snapshot for reading with the Snapshot() method.
	// Returns true if another snapshot is available. Returns false if no more
	// snapshots are available or if an error occured.
	Next() bool

	// Returns an error that occurred during iteration.
	Err() error

	// Returns metadata for the currently positioned snapshot.
	Snapshot() SnapshotInfo
}

SnapshotIterator represents an iterator over a collection of snapshot metadata.

type WALInfo added in v0.2.0 

type WALInfo struct {
	Generation string
	Index      int
	CreatedAt  time.Time
}

WALInfo represents file information about a WAL file.

type WALInfoSlice added in v0.3.5 

type WALInfoSlice []WALInfo

WALInfoSlice represents a slice of WAL metadata.

func (WALInfoSlice) Len added in v0.3.5 

func (a WALInfoSlice) Len() int

func (WALInfoSlice) Less added in v0.3.5 

func (a WALInfoSlice) Less(i, j int) bool

func (WALInfoSlice) Swap added in v0.3.5 

func (a WALInfoSlice) Swap(i, j int)

type WALSegmentInfo added in v0.3.5 

type WALSegmentInfo struct {
	Generation string
	Index      int
	Offset     int64
	Size       int64
	CreatedAt  time.Time
}

WALSegmentInfo represents file information about a WAL segment file.

func SliceWALSegmentIterator added in v0.3.5 

func SliceWALSegmentIterator(itr WALSegmentIterator) ([]WALSegmentInfo, error)

SliceWALSegmentIterator returns all WAL segment files from an iterator as a slice.

func (*WALSegmentInfo) Pos added in v0.3.5 

func (info *WALSegmentInfo) Pos() Pos

Pos returns the WAL position when the segment was made.

type WALSegmentInfoSlice added in v0.3.5 

type WALSegmentInfoSlice []WALSegmentInfo

WALSegmentInfoSlice represents a slice of WAL segment metadata.

func (WALSegmentInfoSlice) Len added in v0.3.5 

func (a WALSegmentInfoSlice) Len() int

func (WALSegmentInfoSlice) Less added in v0.3.5 

func (a WALSegmentInfoSlice) Less(i, j int) bool

func (WALSegmentInfoSlice) Swap added in v0.3.5 

func (a WALSegmentInfoSlice) Swap(i, j int)

type WALSegmentInfoSliceIterator added in v0.3.5 

type WALSegmentInfoSliceIterator struct {
	// contains filtered or unexported fields
}

WALSegmentInfoSliceIterator represents an iterator for iterating over a slice of wal segments.

func NewWALSegmentInfoSliceIterator added in v0.3.5 

func NewWALSegmentInfoSliceIterator(a []WALSegmentInfo) *WALSegmentInfoSliceIterator

NewWALSegmentInfoSliceIterator returns a new instance of WALSegmentInfoSliceIterator.

func (*WALSegmentInfoSliceIterator) Close added in v0.3.5 

func (itr *WALSegmentInfoSliceIterator) Close() error

Close always returns nil.

func (*WALSegmentInfoSliceIterator) Err added in v0.3.5 

func (itr *WALSegmentInfoSliceIterator) Err() error

Err always returns nil.

func (*WALSegmentInfoSliceIterator) Next added in v0.3.5 

func (itr *WALSegmentInfoSliceIterator) Next() bool

Next moves to the next wal segment. Returns true if another segment is available.

func (*WALSegmentInfoSliceIterator) WALSegment added in v0.3.5 

func (itr *WALSegmentInfoSliceIterator) WALSegment() WALSegmentInfo

WALSegment returns the metadata from the currently positioned wal segment.

type WALSegmentIterator added in v0.3.5 

type WALSegmentIterator interface {
	io.Closer

	// Prepares the the next WAL for reading with the WAL() method.
	// Returns true if another WAL is available. Returns false if no more
	// WAL files are available or if an error occured.
	Next() bool

	// Returns an error that occurred during iteration.
	Err() error

	// Returns metadata for the currently positioned WAL segment file.
	WALSegment() WALSegmentInfo
}

WALSegmentIterator represents an iterator over a collection of WAL segments.

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