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replica.go
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replica.go
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package litestream
import (
"context"
"encoding/binary"
"fmt"
"hash/crc64"
"io"
"log/slog"
"math"
"os"
"path/filepath"
"sort"
"sync"
"time"
"filippo.io/age"
"github.com/benbjohnson/litestream/internal"
"github.com/pierrec/lz4/v4"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promauto"
"golang.org/x/sync/errgroup"
)
// Default replica settings.
const (
DefaultSyncInterval = 1 * time.Second
DefaultRetention = 24 * time.Hour
DefaultRetentionCheckInterval = 1 * time.Hour
)
// Replica connects a database to a replication destination via a ReplicaClient.
// The replica manages periodic synchronization and maintaining the current
// replica position.
type Replica struct {
db *DB
name string
mu sync.RWMutex
pos Pos // current replicated position
muf sync.Mutex
f *os.File // long-running file descriptor to avoid non-OFD lock issues
wg sync.WaitGroup
cancel func()
// 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
// Encryption identities and recipients
AgeIdentities []age.Identity
AgeRecipients []age.Recipient
}
func NewReplica(db *DB, name string) *Replica {
r := &Replica{
db: db,
name: name,
cancel: func() {},
SyncInterval: DefaultSyncInterval,
Retention: DefaultRetention,
RetentionCheckInterval: DefaultRetentionCheckInterval,
MonitorEnabled: true,
}
return r
}
// Name returns the name of the replica.
func (r *Replica) Name() string {
if r.name == "" && r.Client != nil {
return r.Client.Type()
}
return r.name
}
// Logger returns the DB sub-logger for this replica.
func (r *Replica) Logger() *slog.Logger {
logger := slog.Default()
if r.db != nil {
logger = r.db.Logger
}
return logger.With("replica", r.Name())
}
// DB returns a reference to the database the replica is attached to, if any.
func (r *Replica) DB() *DB { return r.db }
// Starts replicating in a background goroutine.
func (r *Replica) Start(ctx context.Context) error {
// Ignore if replica is being used sychronously.
if !r.MonitorEnabled {
return nil
}
// Stop previous replication.
r.Stop(false)
// Wrap context with cancelation.
ctx, r.cancel = context.WithCancel(ctx)
// Start goroutine to replicate data.
r.wg.Add(4)
go func() { defer r.wg.Done(); r.monitor(ctx) }()
go func() { defer r.wg.Done(); r.retainer(ctx) }()
go func() { defer r.wg.Done(); r.snapshotter(ctx) }()
go func() { defer r.wg.Done(); r.validator(ctx) }()
return nil
}
// 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 (r *Replica) Stop(hard bool) (err error) {
r.cancel()
r.wg.Wait()
r.muf.Lock()
defer r.muf.Unlock()
if hard && r.f != nil {
if e := r.f.Close(); e != nil && err == nil {
err = e
}
}
return err
}
// Sync copies new WAL frames from the shadow WAL to the replica client.
func (r *Replica) Sync(ctx context.Context) (err error) {
// Clear last position if if an error occurs during sync.
defer func() {
if err != nil {
r.mu.Lock()
r.pos = Pos{}
r.mu.Unlock()
}
}()
// Find current position of database.
dpos, err := r.db.Pos()
if err != nil {
return fmt.Errorf("cannot determine current generation: %w", err)
} else if dpos.IsZero() {
return fmt.Errorf("no generation, waiting for data")
}
generation := dpos.Generation
r.Logger().Debug("replica sync", "position", dpos.String())
// Create a new snapshot and update the current replica position if
// the generation on the database has changed.
if r.Pos().Generation != generation {
// Create snapshot if no snapshots exist for generation.
snapshotN, err := r.snapshotN(ctx, generation)
if err != nil {
return err
} else if snapshotN == 0 {
if info, err := r.Snapshot(ctx); err != nil {
return err
} else if info.Generation != generation {
return fmt.Errorf("generation changed during snapshot, exiting sync")
}
}
pos, err := r.calcPos(ctx, generation)
if err != nil {
return fmt.Errorf("cannot determine replica position: %s", err)
}
r.Logger().Debug("replica sync: calc new pos", "position", pos.String())
r.mu.Lock()
r.pos = pos
r.mu.Unlock()
}
// Read all WAL files since the last position.
for {
if err = r.syncWAL(ctx); err == io.EOF {
break
} else if err != nil {
return err
}
}
return nil
}
func (r *Replica) syncWAL(ctx context.Context) (err error) {
rd, err := r.db.ShadowWALReader(r.Pos())
if err == io.EOF {
return err
} else if err != nil {
return fmt.Errorf("replica wal reader: %w", err)
}
defer rd.Close()
// Copy shadow WAL to client write via io.Pipe().
pr, pw := io.Pipe()
defer func() { _ = pw.CloseWithError(err) }()
// Obtain initial position from shadow reader.
// It may have moved to the next index if previous position was at the end.
pos := rd.Pos()
initialPos := pos
startTime := time.Now()
var bytesWritten int
logger := r.Logger()
logger.Info("write wal segment", "position", initialPos.String())
// Copy through pipe into client from the starting position.
var g errgroup.Group
g.Go(func() error {
_, err := r.Client.WriteWALSegment(ctx, pos, pr)
// Always close pipe reader to signal writers.
if e := pr.CloseWithError(err); err == nil {
return e
}
return err
})
var ew io.WriteCloser = pw
// Add encryption if we have recipients.
if len(r.AgeRecipients) > 0 {
var err error
ew, err = age.Encrypt(pw, r.AgeRecipients...)
if err != nil {
return err
}
defer ew.Close()
}
// Wrap writer to LZ4 compress.
zw := lz4.NewWriter(ew)
// Track total WAL bytes written to replica client.
walBytesCounter := replicaWALBytesCounterVec.WithLabelValues(r.db.Path(), r.Name())
// Copy header if at offset zero.
var psalt uint64 // previous salt value
if pos := rd.Pos(); pos.Offset == 0 {
buf := make([]byte, WALHeaderSize)
if _, err := io.ReadFull(rd, buf); err != nil {
return err
}
psalt = binary.BigEndian.Uint64(buf[16:24])
n, err := zw.Write(buf)
if err != nil {
return err
}
walBytesCounter.Add(float64(n))
bytesWritten += n
}
// Copy frames.
for {
pos := rd.Pos()
assert(pos.Offset == frameAlign(pos.Offset, r.db.pageSize), "shadow wal reader not frame aligned")
buf := make([]byte, WALFrameHeaderSize+r.db.pageSize)
if _, err := io.ReadFull(rd, buf); err == io.EOF {
break
} else if err != nil {
return err
}
// Verify salt matches the previous frame/header read.
salt := binary.BigEndian.Uint64(buf[8:16])
if psalt != 0 && psalt != salt {
return fmt.Errorf("replica salt mismatch: %s", pos.String())
}
psalt = salt
n, err := zw.Write(buf)
if err != nil {
return err
}
walBytesCounter.Add(float64(n))
bytesWritten += n
}
// Flush LZ4 writer, encryption writer and close pipe.
if err := zw.Close(); err != nil {
return err
} else if err := ew.Close(); err != nil {
return err
} else if err := pw.Close(); err != nil {
return err
}
// Wait for client to finish write.
if err := g.Wait(); err != nil {
return fmt.Errorf("client write: %w", err)
}
// Save last replicated position.
r.mu.Lock()
r.pos = rd.Pos()
r.mu.Unlock()
// Track current position
replicaWALIndexGaugeVec.WithLabelValues(r.db.Path(), r.Name()).Set(float64(rd.Pos().Index))
replicaWALOffsetGaugeVec.WithLabelValues(r.db.Path(), r.Name()).Set(float64(rd.Pos().Offset))
logger.Info("wal segment written", "position", initialPos.String(), "elapsed", time.Since(startTime).String(), "sz", bytesWritten)
return nil
}
// snapshotN returns the number of snapshots for a generation.
func (r *Replica) snapshotN(ctx context.Context, generation string) (int, error) {
itr, err := r.Client.Snapshots(ctx, generation)
if err != nil {
return 0, err
}
defer itr.Close()
var n int
for itr.Next() {
n++
}
return n, itr.Close()
}
// calcPos returns the last position for the given generation.
func (r *Replica) calcPos(ctx context.Context, generation string) (pos Pos, err error) {
// Fetch last snapshot. Return error if no snapshots exist.
snapshot, err := r.maxSnapshot(ctx, generation)
if err != nil {
return pos, fmt.Errorf("max snapshot: %w", err)
} else if snapshot == nil {
return pos, fmt.Errorf("no snapshot available: generation=%s", generation)
}
// Determine last WAL segment available. Use snapshot if none exist.
segment, err := r.maxWALSegment(ctx, generation)
if err != nil {
return pos, fmt.Errorf("max wal segment: %w", err)
} else if segment == nil {
return Pos{Generation: snapshot.Generation, Index: snapshot.Index}, nil
}
// Read segment to determine size to add to offset.
rd, err := r.Client.WALSegmentReader(ctx, segment.Pos())
if err != nil {
return pos, fmt.Errorf("wal segment reader: %w", err)
}
defer rd.Close()
if len(r.AgeIdentities) > 0 {
drd, err := age.Decrypt(rd, r.AgeIdentities...)
if err != nil {
return pos, err
}
rd = io.NopCloser(drd)
}
n, err := io.Copy(io.Discard, lz4.NewReader(rd))
if err != nil {
return pos, err
}
// Return the position at the end of the last WAL segment.
return Pos{
Generation: segment.Generation,
Index: segment.Index,
Offset: segment.Offset + n,
}, nil
}
// maxSnapshot returns the last snapshot in a generation.
func (r *Replica) maxSnapshot(ctx context.Context, generation string) (*SnapshotInfo, error) {
itr, err := r.Client.Snapshots(ctx, generation)
if err != nil {
return nil, err
}
defer itr.Close()
var max *SnapshotInfo
for itr.Next() {
if info := itr.Snapshot(); max == nil || info.Index > max.Index {
max = &info
}
}
return max, itr.Close()
}
// maxWALSegment returns the highest WAL segment in a generation.
func (r *Replica) maxWALSegment(ctx context.Context, generation string) (*WALSegmentInfo, error) {
itr, err := r.Client.WALSegments(ctx, generation)
if err != nil {
return nil, err
}
defer itr.Close()
var max *WALSegmentInfo
for itr.Next() {
if info := itr.WALSegment(); max == nil || info.Index > max.Index || (info.Index == max.Index && info.Offset > max.Offset) {
max = &info
}
}
return max, itr.Close()
}
// Pos returns the current replicated position.
// Returns a zero value if the current position cannot be determined.
func (r *Replica) Pos() Pos {
r.mu.RLock()
defer r.mu.RUnlock()
return r.pos
}
// Snapshots returns a list of all snapshots across all generations.
func (r *Replica) Snapshots(ctx context.Context) ([]SnapshotInfo, error) {
generations, err := r.Client.Generations(ctx)
if err != nil {
return nil, fmt.Errorf("cannot fetch generations: %w", err)
}
var a []SnapshotInfo
for _, generation := range generations {
if err := func() error {
itr, err := r.Client.Snapshots(ctx, generation)
if err != nil {
return err
}
defer itr.Close()
other, err := SliceSnapshotIterator(itr)
if err != nil {
return err
}
a = append(a, other...)
return itr.Close()
}(); err != nil {
return a, err
}
}
sort.Sort(SnapshotInfoSlice(a))
return a, nil
}
// Snapshot copies the entire database to the replica path.
func (r *Replica) Snapshot(ctx context.Context) (info SnapshotInfo, err error) {
if r.db == nil || r.db.db == nil {
return info, fmt.Errorf("no database available")
}
r.muf.Lock()
defer r.muf.Unlock()
// Issue a passive checkpoint to flush any pages to disk before snapshotting.
if err := r.db.Checkpoint(ctx, CheckpointModePassive); err != nil {
return info, fmt.Errorf("pre-snapshot checkpoint: %w", err)
}
// Prevent internal checkpoints during snapshot.
r.db.BeginSnapshot()
defer r.db.EndSnapshot()
// Acquire a read lock on the database during snapshot to prevent external checkpoints.
tx, err := r.db.db.Begin()
if err != nil {
return info, err
} else if _, err := tx.ExecContext(ctx, `SELECT COUNT(1) FROM _litestream_seq;`); err != nil {
_ = tx.Rollback()
return info, err
}
defer func() { _ = tx.Rollback() }()
// Obtain current position.
pos, err := r.db.Pos()
if err != nil {
return info, fmt.Errorf("cannot determine db position: %w", err)
} else if pos.IsZero() {
return info, ErrNoGeneration
}
// Open db file descriptor, if not already open, & position at beginning.
if r.f == nil {
if r.f, err = os.Open(r.db.Path()); err != nil {
return info, err
}
}
if _, err := r.f.Seek(0, io.SeekStart); err != nil {
return info, err
}
// Use a pipe to convert the LZ4 writer to a reader.
pr, pw := io.Pipe()
// Copy the database file to the LZ4 writer in a separate goroutine.
var g errgroup.Group
g.Go(func() error {
// We need to ensure the pipe is closed.
defer pw.Close()
var wc io.WriteCloser = pw
// Add encryption if we have recipients.
if len(r.AgeRecipients) > 0 {
var err error
wc, err = age.Encrypt(pw, r.AgeRecipients...)
if err != nil {
pw.CloseWithError(err)
return err
}
defer wc.Close()
}
zr := lz4.NewWriter(wc)
defer zr.Close()
if _, err := io.Copy(zr, r.f); err != nil {
pw.CloseWithError(err)
return err
} else if err := zr.Close(); err != nil {
pw.CloseWithError(err)
return err
}
return wc.Close()
})
logger := r.Logger()
logger.Info("write snapshot", "position", pos.String())
startTime := time.Now()
// Delegate write to client & wait for writer goroutine to finish.
if info, err = r.Client.WriteSnapshot(ctx, pos.Generation, pos.Index, pr); err != nil {
return info, err
} else if err := g.Wait(); err != nil {
return info, err
}
logger.Info("snapshot written", "position", pos.String(), "elapsed", time.Since(startTime).String(), "sz", info.Size)
return info, nil
}
// EnforceRetention forces a new snapshot once the retention interval has passed.
// Older snapshots and WAL files are then removed.
func (r *Replica) EnforceRetention(ctx context.Context) (err error) {
// Obtain list of snapshots that are within the retention period.
snapshots, err := r.Snapshots(ctx)
if err != nil {
return fmt.Errorf("snapshots: %w", err)
}
retained := FilterSnapshotsAfter(snapshots, time.Now().Add(-r.Retention))
// If no retained snapshots exist, create a new snapshot.
if len(retained) == 0 {
snapshot, err := r.Snapshot(ctx)
if err != nil {
return fmt.Errorf("snapshot: %w", err)
}
retained = append(retained, snapshot)
}
// Loop over generations and delete unretained snapshots & WAL files.
generations, err := r.Client.Generations(ctx)
if err != nil {
return fmt.Errorf("generations: %w", err)
}
for _, generation := range generations {
// Find earliest retained snapshot for this generation.
snapshot := FindMinSnapshotByGeneration(retained, generation)
// Delete entire generation if no snapshots are being retained.
if snapshot == nil {
if err := r.Client.DeleteGeneration(ctx, generation); err != nil {
return fmt.Errorf("delete generation: %w", err)
}
continue
}
// Otherwise remove all earlier snapshots & WAL segments.
if err := r.deleteSnapshotsBeforeIndex(ctx, generation, snapshot.Index); err != nil {
return fmt.Errorf("delete snapshots before index: %w", err)
} else if err := r.deleteWALSegmentsBeforeIndex(ctx, generation, snapshot.Index); err != nil {
return fmt.Errorf("delete wal segments before index: %w", err)
}
}
return nil
}
func (r *Replica) deleteSnapshotsBeforeIndex(ctx context.Context, generation string, index int) error {
itr, err := r.Client.Snapshots(ctx, generation)
if err != nil {
return fmt.Errorf("fetch snapshots: %w", err)
}
defer itr.Close()
for itr.Next() {
info := itr.Snapshot()
if info.Index >= index {
continue
}
if err := r.Client.DeleteSnapshot(ctx, info.Generation, info.Index); err != nil {
return fmt.Errorf("delete snapshot %s/%08x: %w", info.Generation, info.Index, err)
}
r.Logger().Info("snapshot deleted", "generation", generation, "index", index)
}
return itr.Close()
}
func (r *Replica) deleteWALSegmentsBeforeIndex(ctx context.Context, generation string, index int) error {
itr, err := r.Client.WALSegments(ctx, generation)
if err != nil {
return fmt.Errorf("fetch wal segments: %w", err)
}
defer itr.Close()
var a []Pos
for itr.Next() {
info := itr.WALSegment()
if info.Index >= index {
continue
}
a = append(a, info.Pos())
}
if err := itr.Close(); err != nil {
return err
}
if len(a) == 0 {
return nil
}
if err := r.Client.DeleteWALSegments(ctx, a); err != nil {
return fmt.Errorf("delete wal segments: %w", err)
}
r.Logger().Info("wal segmented deleted before", "generation", generation, "index", index, "n", len(a))
return nil
}
// monitor runs in a separate goroutine and continuously replicates the DB.
func (r *Replica) monitor(ctx context.Context) {
ticker := time.NewTicker(r.SyncInterval)
defer ticker.Stop()
// Continuously check for new data to replicate.
ch := make(chan struct{})
close(ch)
var notify <-chan struct{} = ch
for initial := true; ; initial = false {
// Enforce a minimum time between synchronization.
if !initial {
select {
case <-ctx.Done():
return
case <-ticker.C:
}
}
// Wait for changes to the database.
select {
case <-ctx.Done():
return
case <-notify:
}
// Fetch new notify channel before replicating data.
notify = r.db.Notify()
// Synchronize the shadow wal into the replication directory.
if err := r.Sync(ctx); err != nil {
r.Logger().Error("monitor error", "error", err)
continue
}
}
}
// retainer runs in a separate goroutine and handles retention.
func (r *Replica) retainer(ctx context.Context) {
// Disable retention enforcement if retention period is non-positive.
if r.Retention <= 0 {
return
}
// Ensure check interval is not longer than retention period.
checkInterval := r.RetentionCheckInterval
if checkInterval > r.Retention {
checkInterval = r.Retention
}
ticker := time.NewTicker(checkInterval)
defer ticker.Stop()
for {
select {
case <-ctx.Done():
return
case <-ticker.C:
if err := r.EnforceRetention(ctx); err != nil {
r.Logger().Error("retainer error", "error", err)
continue
}
}
}
}
// snapshotter runs in a separate goroutine and handles snapshotting.
func (r *Replica) snapshotter(ctx context.Context) {
if r.SnapshotInterval <= 0 {
return
}
logger := r.Logger()
if pos, err := r.db.Pos(); err != nil {
logger.Error("snapshotter cannot determine generation", "error", err)
} else if !pos.IsZero() {
if snapshot, err := r.maxSnapshot(ctx, pos.Generation); err != nil {
logger.Error("snapshotter cannot determine latest snapshot", "error", err)
} else if snapshot != nil {
nextSnapshot := r.SnapshotInterval - time.Since(snapshot.CreatedAt)
if nextSnapshot < 0 {
nextSnapshot = 0
}
logger.Info("snapshot interval adjusted", "previous", snapshot.CreatedAt.Format(time.RFC3339), "next", nextSnapshot.String())
select {
case <-ctx.Done():
return
case <-time.After(nextSnapshot):
if _, err := r.Snapshot(ctx); err != nil && err != ErrNoGeneration {
logger.Error("snapshotter error", "error", err)
}
}
}
}
ticker := time.NewTicker(r.SnapshotInterval)
defer ticker.Stop()
for {
select {
case <-ctx.Done():
return
case <-ticker.C:
if _, err := r.Snapshot(ctx); err != nil && err != ErrNoGeneration {
r.Logger().Error("snapshotter error", "error", err)
continue
}
}
}
}
// validator runs in a separate goroutine and handles periodic validation.
func (r *Replica) validator(ctx context.Context) {
// Initialize counters since validation occurs infrequently.
for _, status := range []string{"ok", "error"} {
replicaValidationTotalCounterVec.WithLabelValues(r.db.Path(), r.Name(), status).Add(0)
}
// Exit validation if interval is not set.
if r.ValidationInterval <= 0 {
return
}
ticker := time.NewTicker(r.ValidationInterval)
defer ticker.Stop()
for {
select {
case <-ctx.Done():
return
case <-ticker.C:
if err := r.Validate(ctx); err != nil {
r.Logger().Error("validation error", "error", err)
continue
}
}
}
}
// Validate restores the most recent data from a replica and validates
// that the resulting database matches the current database.
func (r *Replica) Validate(ctx context.Context) error {
db := r.DB()
// Restore replica to a temporary directory.
tmpdir, err := os.MkdirTemp("", "*-litestream")
if err != nil {
return err
}
defer os.RemoveAll(tmpdir)
// Compute checksum of primary database under lock. This prevents a
// sync from occurring and the database will not be written.
chksum0, pos, err := db.CRC64(ctx)
if err != nil {
return fmt.Errorf("cannot compute checksum: %w", err)
}
// Wait until replica catches up to position.
if err := r.waitForReplica(ctx, pos); err != nil {
return fmt.Errorf("cannot wait for replica: %w", err)
}
restorePath := filepath.Join(tmpdir, "replica")
if err := r.Restore(ctx, RestoreOptions{
OutputPath: restorePath,
ReplicaName: r.Name(),
Generation: pos.Generation,
Index: pos.Index - 1,
}); err != nil {
return fmt.Errorf("cannot restore: %w", err)
}
// Open file handle for restored database.
// NOTE: This open is ok as the restored database is not managed by litestream.
f, err := os.Open(restorePath)
if err != nil {
return err
}
defer f.Close()
// Read entire file into checksum.
h := crc64.New(crc64.MakeTable(crc64.ISO))
if _, err := io.Copy(h, f); err != nil {
return err
}
chksum1 := h.Sum64()
status := "ok"
mismatch := chksum0 != chksum1
if mismatch {
status = "mismatch"
}
r.Logger().Info("validator", "status", status, "db", fmt.Sprintf("%016x", chksum0), "replica", fmt.Sprintf("%016x", chksum1), "position", pos.String())
// Validate checksums match.
if mismatch {
replicaValidationTotalCounterVec.WithLabelValues(r.db.Path(), r.Name(), "error").Inc()
return ErrChecksumMismatch
}
replicaValidationTotalCounterVec.WithLabelValues(r.db.Path(), r.Name(), "ok").Inc()
if err := os.RemoveAll(tmpdir); err != nil {
return fmt.Errorf("cannot remove temporary validation directory: %w", err)
}
return nil
}
// waitForReplica blocks until replica reaches at least the given position.
func (r *Replica) waitForReplica(ctx context.Context, pos Pos) error {
ticker := time.NewTicker(500 * time.Millisecond)
defer ticker.Stop()
timer := time.NewTicker(10 * time.Second)
defer ticker.Stop()
once := make(chan struct{}, 1)
once <- struct{}{}
for {
select {
case <-ctx.Done():
return ctx.Err()
case <-timer.C:
return fmt.Errorf("replica wait exceeded timeout")
case <-ticker.C:
case <-once: // immediate on first check
}
// Obtain current position of replica, check if past target position.
curr := r.Pos()
if curr.IsZero() {
r.Logger().Info("validator: no replica position available")
continue
}
// Exit if the generation has changed while waiting as there will be
// no further progress on the old generation.
if curr.Generation != pos.Generation {
return fmt.Errorf("generation changed")
}
ready := true
if curr.Index < pos.Index {
ready = false
} else if curr.Index == pos.Index && curr.Offset < pos.Offset {
ready = false
}
// If not ready, restart loop.
if !ready {
continue
}
// Current position at or after target position.
return nil
}
}
// GenerationCreatedAt returns the earliest creation time of any snapshot.
// Returns zero time if no snapshots exist.
func (r *Replica) GenerationCreatedAt(ctx context.Context, generation string) (time.Time, error) {
var min time.Time
itr, err := r.Client.Snapshots(ctx, generation)
if err != nil {
return min, err
}
defer itr.Close()
for itr.Next() {
if info := itr.Snapshot(); min.IsZero() || info.CreatedAt.Before(min) {
min = info.CreatedAt
}
}
return min, itr.Close()
}
// GenerationTimeBounds returns the creation time & last updated time of a generation.
// Returns zero time if no snapshots or WAL segments exist.
func (r *Replica) GenerationTimeBounds(ctx context.Context, generation string) (createdAt, updatedAt time.Time, err error) {
// Iterate over snapshots.
sitr, err := r.Client.Snapshots(ctx, generation)
if err != nil {
return createdAt, updatedAt, err
}
defer sitr.Close()
minIndex, maxIndex := -1, -1
for sitr.Next() {
info := sitr.Snapshot()
if createdAt.IsZero() || info.CreatedAt.Before(createdAt) {
createdAt = info.CreatedAt
}
if updatedAt.IsZero() || info.CreatedAt.After(updatedAt) {
updatedAt = info.CreatedAt
}
if minIndex == -1 || info.Index < minIndex {
minIndex = info.Index
}
if info.Index > maxIndex {
maxIndex = info.Index
}
}
if err := sitr.Close(); err != nil {
return createdAt, updatedAt, err
}
// Iterate over WAL segments.
witr, err := r.Client.WALSegments(ctx, generation)
if err != nil {
return createdAt, updatedAt, err
}
defer witr.Close()
for witr.Next() {
info := witr.WALSegment()
if info.Index < minIndex || info.Index > maxIndex {
continue
}
if createdAt.IsZero() || info.CreatedAt.Before(createdAt) {
createdAt = info.CreatedAt
}
if updatedAt.IsZero() || info.CreatedAt.After(updatedAt) {
updatedAt = info.CreatedAt