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Add retention policy, remove WAL subdir

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This commit is contained in:
Ben Johnson
2021-01-11 16:49:51 -07:00
parent 1fa1313b0b
commit faa5765745
4 changed files with 240 additions and 152 deletions
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10
cmd/litestream/main.go
View File

@@ -10,6 +10,7 @@ import (
"os/user"
"path/filepath"
"strings"
"time"
"github.com/benbjohnson/litestream"
"gopkg.in/yaml.v2"
@@ -157,7 +158,8 @@ type DBConfig struct {
type ReplicaConfig struct {
Type string `yaml:"type"` // "file", "s3"
Name string `yaml:"name"` // name of replica, optional.
Path string `yaml:"path"` // used for file replicas
Path string `yaml:"path"`
Retention time.Duration `yaml:"retention"`
}
func registerConfigFlag(fs *flag.FlagSet, p *string) {
@@ -196,5 +198,9 @@ func newFileReplicaFromConfig(db *litestream.DB, config *ReplicaConfig) (*litest
if config.Path == "" {
return nil, fmt.Errorf("file replica path require for db %q", db.Path())
}
return litestream.NewFileReplica(db, config.Name, config.Path), nil
r := litestream.NewFileReplica(db, config.Name, config.Path)
if v := config.Retention; v > 0 {
r.RetentionInterval = v
}
return r, nil
}

2
db.go
View File

@@ -31,6 +31,7 @@ const (
DefaultCheckpointInterval = 1 * time.Minute
DefaultMinCheckpointPageN = 1000
DefaultMaxCheckpointPageN = 10000
DefaultRetentionInterval = 24 * time.Hour
)
// DB represents a managed instance of a SQLite database in the file system.
@@ -41,6 +42,7 @@ type DB struct {
rtx *sql.Tx // long running read transaction
pageSize int // page size, in bytes
notify chan struct{} // closes on WAL change
uid, gid int // db user/group obtained on init
ctx context.Context

32
litestream.go
View File

@@ -52,6 +52,30 @@ type SnapshotInfo struct {
CreatedAt time.Time
}
// filterSnapshotsAfter returns all snapshots that were created on or after t.
func filterSnapshotsAfter(a []*SnapshotInfo, t time.Time) []*SnapshotInfo {
other := make([]*SnapshotInfo, 0, len(a))
for _, snapshot := range a {
if !snapshot.CreatedAt.Before(t) {
other = append(other, snapshot)
}
}
return other
}
// findMinSnapshotByGeneration finds the snapshot with the lowest index in a generation.
func findMinSnapshotByGeneration(a []*SnapshotInfo, generation string) *SnapshotInfo {
var min *SnapshotInfo
for _, snapshot := range a {
if snapshot.Generation != generation {
continue
} else if min == nil || snapshot.Index < min.Index {
min = snapshot
}
}
return min
}
// WALInfo represents file information about a WAL file.
type WALInfo struct {
Name string
@@ -184,19 +208,19 @@ func IsSnapshotPath(s string) bool {
// ParseSnapshotPath returns the index for the snapshot.
// Returns an error if the path is not a valid snapshot path.
func ParseSnapshotPath(s string) (index int, typ, ext string, err error) {
func ParseSnapshotPath(s string) (index int, ext string, err error) {
s = filepath.Base(s)
a := snapshotPathRegex.FindStringSubmatch(s)
if a == nil {
return 0, "", "", fmt.Errorf("invalid snapshot path: %s", s)
return 0, "", fmt.Errorf("invalid snapshot path: %s", s)
}
i64, _ := strconv.ParseUint(a[1], 16, 64)
return int(i64), a[2], a[3], nil
return int(i64), a[2], nil
}
var snapshotPathRegex = regexp.MustCompile(`^([0-9a-f]{16})(?:-(\w+))?(.snapshot(?:.gz)?)$`)
var snapshotPathRegex = regexp.MustCompile(`^([0-9a-f]{16})(.snapshot(?:.gz)?)$`)
// IsWALPath returns true if s is a path to a WAL file.
func IsWALPath(s string) bool {

256
replica.go
View File

@@ -11,7 +11,6 @@ import (
"os"
"path/filepath"
"sort"
"strconv"
"sync"
"time"
)
@@ -90,6 +89,10 @@ type FileReplica struct {
ctx context.Context
cancel func()
// Time to keep snapshots and related WAL files.
// Database is snapshotted after interval and older WAL files are discarded.
RetentionInterval 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
@@ -103,6 +106,7 @@ func NewFileReplica(db *DB, name, dst string) *FileReplica {
dst: dst,
cancel: func() {},
RetentionInterval: DefaultRetentionInterval,
MonitorEnabled: true,
}
}
@@ -127,9 +131,14 @@ func (r *FileReplica) LastPos() Pos {
return r.pos
}
// GenerationDir returns the path to a generation's root directory.
func (r *FileReplica) GenerationDir(generation string) string {
return filepath.Join(r.dst, "generations", generation)
}
// SnapshotDir returns the path to a generation's snapshot directory.
func (r *FileReplica) SnapshotDir(generation string) string {
return filepath.Join(r.dst, "generations", generation, "snapshots")
return filepath.Join(r.GenerationDir(generation), "snapshots")
}
// SnapshotPath returns the path to a snapshot file.
@@ -146,7 +155,7 @@ func (r *FileReplica) MaxSnapshotIndex(generation string) (int, error) {
index := -1
for _, fi := range fis {
if idx, _, _, err := ParseSnapshotPath(fi.Name()); err != nil {
if idx, _, err := ParseSnapshotPath(fi.Name()); err != nil {
continue
} else if index == -1 || idx > index {
index = idx
@@ -160,55 +169,12 @@ func (r *FileReplica) MaxSnapshotIndex(generation string) (int, error) {
// WALDir returns the path to a generation's WAL directory
func (r *FileReplica) WALDir(generation string) string {
return filepath.Join(r.dst, "generations", generation, "wal")
}
// WALSubdir returns the directory used for grouping WAL files.
func (r *FileReplica) WALSubdir(generation string, index int) string {
return filepath.Join(r.WALDir(generation), fmt.Sprintf("%016x", uint64(index)&walDirMask))
}
// WALSubdirNames returns a list of all WAL subdirectory group names.
func (r *FileReplica) WALSubdirNames(generation string) ([]string, error) {
fis, err := ioutil.ReadDir(r.WALDir(generation))
if err != nil && !os.IsNotExist(err) {
return nil, err
}
var names []string
for _, fi := range fis {
if _, err := strconv.ParseUint(fi.Name(), 16, 64); err != nil {
continue
}
names = append(names, fi.Name())
}
return names, nil
}
// MaxWALSubdirName returns the highest WAL subdirectory group name.
func (r *FileReplica) MaxWALSubdirName(generation string) (string, error) {
fis, err := ioutil.ReadDir(r.WALDir(generation))
if err != nil {
return "", err
}
var name string
for _, fi := range fis {
if _, err := strconv.ParseUint(fi.Name(), 16, 64); err != nil {
continue
} else if name == "" || fi.Name() > name {
name = fi.Name()
}
}
if name == "" {
return "", os.ErrNotExist
}
return name, nil
return filepath.Join(r.GenerationDir(generation), "wal")
}
// WALPath returns the path to a WAL file.
func (r *FileReplica) WALPath(generation string, index int) string {
return filepath.Join(r.WALSubdir(generation, index), fmt.Sprintf("%016x.wal", index))
return filepath.Join(r.WALDir(generation), fmt.Sprintf("%016x.wal", index))
}
// Generations returns a list of available generation names.
@@ -286,13 +252,7 @@ func (r *FileReplica) snapshotStats(generation string) (n int, min, max time.Tim
}
func (r *FileReplica) walStats(generation string) (n int, min, max time.Time, err error) {
names, err := r.WALSubdirNames(generation)
if err != nil {
return n, min, max, err
}
for _, name := range names {
fis, err := ioutil.ReadDir(filepath.Join(r.WALDir(generation), name))
fis, err := ioutil.ReadDir(r.WALDir(generation))
if os.IsNotExist(err) {
return n, min, max, nil
} else if err != nil {
@@ -313,7 +273,6 @@ func (r *FileReplica) walStats(generation string) (n int, min, max time.Time, er
max = modTime
}
}
}
return n, min, max, nil
}
@@ -334,7 +293,7 @@ func (r *FileReplica) Snapshots(ctx context.Context) ([]*SnapshotInfo, error) {
}
for _, fi := range fis {
index, _, _, err := ParseSnapshotPath(fi.Name())
index, _, err := ParseSnapshotPath(fi.Name())
if err != nil {
continue
}
@@ -364,23 +323,8 @@ func (r *FileReplica) WALs(ctx context.Context) ([]*WALInfo, error) {
var infos []*WALInfo
for _, generation := range generations {
// Find a list of all directory groups.
dir := r.WALDir(generation)
subfis, err := ioutil.ReadDir(dir)
if os.IsNotExist(err) {
continue
} else if err != nil {
return nil, err
}
// Iterate over WAL group subdirectories.
for _, subfi := range subfis {
if !subfi.IsDir() {
continue
}
// Find a list of all WAL files in the group.
fis, err := ioutil.ReadDir(filepath.Join(dir, subfi.Name()))
// Find a list of all WAL files.
fis, err := ioutil.ReadDir(r.WALDir(generation))
if os.IsNotExist(err) {
continue
} else if err != nil {
@@ -405,7 +349,6 @@ func (r *FileReplica) WALs(ctx context.Context) ([]*WALInfo, error) {
})
}
}
}
return infos, nil
}
@@ -424,8 +367,9 @@ func (r *FileReplica) Start(ctx context.Context) {
ctx, r.cancel = context.WithCancel(ctx)
// Start goroutine to replicate data.
r.wg.Add(1)
r.wg.Add(2)
go func() { defer r.wg.Done(); r.monitor(ctx) }()
go func() { defer r.wg.Done(); r.retainer(ctx) }()
}
// Stop cancels any outstanding replication and blocks until finished.
@@ -464,6 +408,24 @@ func (r *FileReplica) monitor(ctx context.Context) {
}
}
// retainer runs in a separate goroutine and handles retention.
func (r *FileReplica) retainer(ctx context.Context) {
ticker := time.NewTicker(1 * time.Minute)
defer ticker.Stop()
for {
select {
case <-ctx.Done():
return
case <-ticker.C:
if err := r.EnforceRetention(ctx); err != nil {
log.Printf("%s(%s): retain error: %s", r.db.Path(), r.Name(), err)
continue
}
}
}
}
// CalcPos returns the position for the replica for the current generation.
// Returns a zero value if there is no active generation.
func (r *FileReplica) CalcPos(generation string) (pos Pos, err error) {
@@ -474,16 +436,8 @@ func (r *FileReplica) CalcPos(generation string) (pos Pos, err error) {
return Pos{}, err
}
// Find highest WAL subdirectory group.
subdir, err := r.MaxWALSubdirName(generation)
if os.IsNotExist(err) {
return pos, nil // no replicated wal, start at snapshot index
} else if err != nil {
return Pos{}, err
}
// Find the max WAL file within WAL group.
fis, err := ioutil.ReadDir(filepath.Join(r.WALDir(generation), subdir))
// Find the max WAL file within WAL.
fis, err := ioutil.ReadDir(r.WALDir(generation))
if os.IsNotExist(err) {
return pos, nil // no replicated wal, start at snapshot index.
} else if err != nil {
@@ -549,7 +503,7 @@ func (r *FileReplica) snapshotN(generation string) (int, error) {
var n int
for _, fi := range fis {
if _, _, _, err := ParseSnapshotPath(fi.Name()); err == nil {
if _, _, err := ParseSnapshotPath(fi.Name()); err == nil {
n++
}
}
@@ -693,7 +647,7 @@ func (r *FileReplica) SnapshotIndexAt(ctx context.Context, generation string, ti
var max time.Time
for _, fi := range fis {
// Read index from snapshot filename.
idx, _, _, err := ParseSnapshotPath(fi.Name())
idx, _, err := ParseSnapshotPath(fi.Name())
if err != nil {
continue // not a snapshot, skip
} else if !timestamp.IsZero() && fi.ModTime().After(timestamp) {
@@ -715,17 +669,8 @@ func (r *FileReplica) SnapshotIndexAt(ctx context.Context, generation string, ti
// Returns the highest index for a WAL file that occurs before maxIndex & timestamp.
// If timestamp is zero, returns the highest WAL index.
func (r *FileReplica) WALIndexAt(ctx context.Context, generation string, maxIndex int, timestamp time.Time) (int, error) {
names, err := r.WALSubdirNames(generation)
if err != nil {
return 0, err
}
// TODO: Optimize to only read the last group if no timestamp specified.
// TODO: Perform binary search to find correct timestamp.
var index int
for _, name := range names {
fis, err := ioutil.ReadDir(filepath.Join(r.WALDir(generation), name))
fis, err := ioutil.ReadDir(r.WALDir(generation))
if os.IsNotExist(err) {
return 0, nil
} else if err != nil {
@@ -747,7 +692,6 @@ func (r *FileReplica) WALIndexAt(ctx context.Context, generation string, maxInde
index = idx
}
}
// If max index is specified but not found, return an error.
if maxIndex != math.MaxInt64 && index != maxIndex {
@@ -768,7 +712,7 @@ func (r *FileReplica) SnapshotReader(ctx context.Context, generation string, ind
for _, fi := range fis {
// Parse index from snapshot filename. Skip if no match.
idx, _, ext, err := ParseSnapshotPath(fi.Name())
idx, ext, err := ParseSnapshotPath(fi.Name())
if err != nil || index != idx {
continue
}
@@ -823,6 +767,118 @@ func (r *FileReplica) WALReader(ctx context.Context, generation string, index in
return &gzipReadCloser{r: rd, closer: f}, nil
}
// EnforceRetention forces a new snapshot once the retention interval has passed.
// Older snapshots and WAL files are then removed.
func (r *FileReplica) EnforceRetention(ctx context.Context) (err error) {
// Find current position of database.
pos, err := r.db.Pos()
if err != nil {
return fmt.Errorf("cannot determine current generation: %w", err)
} else if pos.IsZero() {
return fmt.Errorf("no generation, waiting for data")
}
// Obtain list of snapshots that are within the retention period.
snapshots, err := r.Snapshots(ctx)
if err != nil {
return fmt.Errorf("cannot obtain snapshot list: %w", err)
}
snapshots = filterSnapshotsAfter(snapshots, time.Now().Add(-r.RetentionInterval))
// If no retained snapshots exist, create a new snapshot.
if len(snapshots) == 0 {
log.Printf("%s(%s): snapshots exceeds retention, creating new snapshot", r.db.Path(), r.Name())
if err := r.snapshot(ctx, pos.Generation, pos.Index); err != nil {
return fmt.Errorf("cannot snapshot: %w", err)
}
snapshots = append(snapshots, &SnapshotInfo{Generation: pos.Generation, Index: pos.Index})
}
// Loop over generations and delete unretained snapshots & WAL files.
generations, err := r.Generations(ctx)
if err != nil {
return fmt.Errorf("cannot obtain generations: %w", err)
}
for _, generation := range generations {
// Find earliest retained snapshot for this generation.
snapshot := findMinSnapshotByGeneration(snapshots, generation)
// Delete generations if it has no snapshots being retained.
if snapshot == nil {
log.Printf("%s(%s): generation %q has no retained snapshots, deleting", r.db.Path(), r.Name(), generation)
if err := os.RemoveAll(r.GenerationDir(generation)); err != nil {
return fmt.Errorf("cannot delete generation %q dir: %w", generation, err)
}
continue
}
// Otherwise delete all snapshots & WAL files before a lowest retained index.
if err := r.deleteGenerationSnapshotsBefore(ctx, generation, snapshot.Index); err != nil {
return fmt.Errorf("cannot delete generation %q snapshots before index %d: %w", generation, snapshot.Index, err)
} else if err := r.deleteGenerationWALBefore(ctx, generation, snapshot.Index); err != nil {
return fmt.Errorf("cannot delete generation %q wal before index %d: %w", generation, snapshot.Index, err)
}
}
return nil
}
// deleteGenerationSnapshotsBefore deletes snapshot before a given index.
func (r *FileReplica) deleteGenerationSnapshotsBefore(ctx context.Context, generation string, index int) (err error) {
dir := r.SnapshotDir(generation)
fis, err := ioutil.ReadDir(dir)
if os.IsNotExist(err) {
return nil
} else if err != nil {
return err
}
for _, fi := range fis {
idx, _, err := ParseSnapshotPath(fi.Name())
if err != nil {
continue
} else if idx >= index {
continue
}
log.Printf("%s(%s): generation %q snapshot no longer retained, deleting %s", r.db.Path(), r.Name(), generation, fi.Name())
if err := os.Remove(filepath.Join(dir, fi.Name())); err != nil {
return err
}
}
return nil
}
// deleteGenerationWALBefore deletes WAL files before a given index.
func (r *FileReplica) deleteGenerationWALBefore(ctx context.Context, generation string, index int) (err error) {
dir := r.WALDir(generation)
fis, err := ioutil.ReadDir(dir)
if os.IsNotExist(err) {
return nil
} else if err != nil {
return err
}
for _, fi := range fis {
idx, _, _, err := ParseWALPath(fi.Name())
if err != nil {
continue
} else if idx >= index {
continue
}
log.Printf("%s(%s): generation %q wal no longer retained, deleting %s", r.db.Path(), r.Name(), generation, fi.Name())
if err := os.Remove(filepath.Join(dir, fi.Name())); err != nil {
return err
}
}
return nil
}
// compressFile compresses a file and replaces it with a new file with a .gz extension.
func compressFile(src, dst string, uid, gid int) error {
r, err := os.Open(src)