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db.go
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/*
* Copyright 2017 Dgraph Labs, Inc. and Contributors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package badger
import (
"encoding/binary"
"expvar"
"log"
"math"
"os"
"path/filepath"
"strconv"
"sync"
"time"
"github.com/dgraph-io/badger/options"
"golang.org/x/net/trace"
"github.com/dgraph-io/badger/skl"
"github.com/dgraph-io/badger/table"
"github.com/dgraph-io/badger/y"
"github.com/pkg/errors"
)
var (
badgerPrefix = []byte("!badger!") // Prefix for internal keys used by badger.
head = []byte("!badger!head") // For storing value offset for replay.
txnKey = []byte("!badger!txn") // For indicating end of entries in txn.
badgerMove = []byte("!badger!move") // For key-value pairs which got moved during GC.
)
type closers struct {
updateSize *y.Closer
compactors *y.Closer
memtable *y.Closer
writes *y.Closer
valueGC *y.Closer
}
// DB provides the various functions required to interact with Badger.
// DB is thread-safe.
type DB struct {
sync.RWMutex // Guards list of inmemory tables, not individual reads and writes.
dirLockGuard *directoryLockGuard
// nil if Dir and ValueDir are the same
valueDirGuard *directoryLockGuard
closers closers
elog trace.EventLog
mt *skl.Skiplist // Our latest (actively written) in-memory table
imm []*skl.Skiplist // Add here only AFTER pushing to flushChan.
opt Options
manifest *manifestFile
lc *levelsController
vlog valueLog
vptr valuePointer // less than or equal to a pointer to the last vlog value put into mt
writeCh chan *request
flushChan chan flushTask // For flushing memtables.
orc *oracle
}
const (
kvWriteChCapacity = 1000
)
func replayFunction(out *DB) func(Entry, valuePointer) error {
type txnEntry struct {
nk []byte
v y.ValueStruct
}
var txn []txnEntry
var lastCommit uint64
toLSM := func(nk []byte, vs y.ValueStruct) {
for err := out.ensureRoomForWrite(); err != nil; err = out.ensureRoomForWrite() {
out.elog.Printf("Replay: Making room for writes")
time.Sleep(10 * time.Millisecond)
}
out.mt.Put(nk, vs)
}
first := true
return func(e Entry, vp valuePointer) error { // Function for replaying.
if first {
out.elog.Printf("First key=%q\n", e.Key)
}
first = false
if out.orc.curRead < y.ParseTs(e.Key) {
out.orc.curRead = y.ParseTs(e.Key)
}
nk := make([]byte, len(e.Key))
copy(nk, e.Key)
var nv []byte
meta := e.meta
if out.shouldWriteValueToLSM(e) {
nv = make([]byte, len(e.Value))
copy(nv, e.Value)
} else {
nv = make([]byte, vptrSize)
vp.Encode(nv)
meta = meta | bitValuePointer
}
v := y.ValueStruct{
Value: nv,
Meta: meta,
UserMeta: e.UserMeta,
}
if e.meta&bitFinTxn > 0 {
txnTs, err := strconv.ParseUint(string(e.Value), 10, 64)
if err != nil {
return errors.Wrapf(err, "Unable to parse txn fin: %q", e.Value)
}
y.AssertTrue(lastCommit == txnTs)
y.AssertTrue(len(txn) > 0)
// Got the end of txn. Now we can store them.
for _, t := range txn {
toLSM(t.nk, t.v)
}
txn = txn[:0]
lastCommit = 0
} else if e.meta&bitTxn == 0 {
// This entry is from a rewrite.
toLSM(nk, v)
// We shouldn't get this entry in the middle of a transaction.
y.AssertTrue(lastCommit == 0)
y.AssertTrue(len(txn) == 0)
} else {
txnTs := y.ParseTs(nk)
if lastCommit == 0 {
lastCommit = txnTs
}
y.AssertTrue(lastCommit == txnTs)
te := txnEntry{nk: nk, v: v}
txn = append(txn, te)
}
return nil
}
}
// Open returns a new DB object.
func Open(opt Options) (db *DB, err error) {
opt.maxBatchSize = (15 * opt.MaxTableSize) / 100
opt.maxBatchCount = opt.maxBatchSize / int64(skl.MaxNodeSize)
if opt.ValueThreshold > math.MaxUint16-16 {
return nil, ErrValueThreshold
}
if opt.ReadOnly {
// Can't truncate if the DB is read only.
opt.Truncate = false
}
for _, path := range []string{opt.Dir, opt.ValueDir} {
dirExists, err := exists(path)
if err != nil {
return nil, y.Wrapf(err, "Invalid Dir: %q", path)
}
if !dirExists {
if opt.ReadOnly {
return nil, y.Wrapf(err, "Cannot find Dir for read-only open: %q", path)
}
// Try to create the directory
err = os.Mkdir(path, 0700)
if err != nil {
return nil, y.Wrapf(err, "Error Creating Dir: %q", path)
}
}
}
absDir, err := filepath.Abs(opt.Dir)
if err != nil {
return nil, err
}
absValueDir, err := filepath.Abs(opt.ValueDir)
if err != nil {
return nil, err
}
var dirLockGuard, valueDirLockGuard *directoryLockGuard
dirLockGuard, err = acquireDirectoryLock(opt.Dir, lockFile, opt.ReadOnly)
if err != nil {
return nil, err
}
defer func() {
if dirLockGuard != nil {
_ = dirLockGuard.release()
}
}()
if absValueDir != absDir {
valueDirLockGuard, err = acquireDirectoryLock(opt.ValueDir, lockFile, opt.ReadOnly)
if err != nil {
return nil, err
}
}
defer func() {
if valueDirLockGuard != nil {
_ = valueDirLockGuard.release()
}
}()
if !(opt.ValueLogFileSize <= 2<<30 && opt.ValueLogFileSize >= 1<<20) {
return nil, ErrValueLogSize
}
if !(opt.ValueLogLoadingMode == options.FileIO ||
opt.ValueLogLoadingMode == options.MemoryMap) {
return nil, ErrInvalidLoadingMode
}
manifestFile, manifest, err := openOrCreateManifestFile(opt.Dir, opt.ReadOnly)
if err != nil {
return nil, err
}
defer func() {
if manifestFile != nil {
_ = manifestFile.close()
}
}()
orc := &oracle{
isManaged: opt.managedTxns,
nextCommit: 1,
commits: make(map[uint64]uint64),
readMark: y.WaterMark{},
}
orc.readMark.Init()
db = &DB{
imm: make([]*skl.Skiplist, 0, opt.NumMemtables),
flushChan: make(chan flushTask, opt.NumMemtables),
writeCh: make(chan *request, kvWriteChCapacity),
opt: opt,
manifest: manifestFile,
elog: trace.NewEventLog("Badger", "DB"),
dirLockGuard: dirLockGuard,
valueDirGuard: valueDirLockGuard,
orc: orc,
}
// Calculate initial size.
db.calculateSize()
db.closers.updateSize = y.NewCloser(1)
go db.updateSize(db.closers.updateSize)
db.mt = skl.NewSkiplist(arenaSize(opt))
// newLevelsController potentially loads files in directory.
if db.lc, err = newLevelsController(db, &manifest); err != nil {
return nil, err
}
if !opt.ReadOnly {
db.closers.compactors = y.NewCloser(1)
db.lc.startCompact(db.closers.compactors)
db.closers.memtable = y.NewCloser(1)
go db.flushMemtable(db.closers.memtable) // Need levels controller to be up.
}
if err = db.vlog.Open(db, opt); err != nil {
return nil, err
}
headKey := y.KeyWithTs(head, math.MaxUint64)
// Need to pass with timestamp, lsm get removes the last 8 bytes and compares key
vs, err := db.get(headKey)
if err != nil {
return nil, errors.Wrap(err, "Retrieving head")
}
db.orc.curRead = vs.Version
var vptr valuePointer
if len(vs.Value) > 0 {
vptr.Decode(vs.Value)
}
// lastUsedCasCounter will either be the value stored in !badger!head, or some subsequently
// written value log entry that we replay. (Subsequent value log entries might be _less_
// than lastUsedCasCounter, if there was value log gc so we have to max() values while
// replaying.)
// out.lastUsedCasCounter = item.casCounter
// TODO: Figure this out. This would update the read timestamp, and set nextCommitTs.
replayCloser := y.NewCloser(1)
go db.doWrites(replayCloser)
if err = db.vlog.Replay(vptr, replayFunction(db)); err != nil {
return db, err
}
replayCloser.SignalAndWait() // Wait for replay to be applied first.
// Now that we have the curRead, we can update the nextCommit.
db.orc.nextCommit = db.orc.curRead + 1
// Mmap writable log
lf := db.vlog.filesMap[db.vlog.maxFid]
if err = lf.mmap(2 * db.vlog.opt.ValueLogFileSize); err != nil {
return db, errors.Wrapf(err, "Unable to mmap RDWR log file")
}
db.writeCh = make(chan *request, kvWriteChCapacity)
db.closers.writes = y.NewCloser(1)
go db.doWrites(db.closers.writes)
db.closers.valueGC = y.NewCloser(1)
go db.vlog.waitOnGC(db.closers.valueGC)
valueDirLockGuard = nil
dirLockGuard = nil
manifestFile = nil
return db, nil
}
// Close closes a DB. It's crucial to call it to ensure all the pending updates
// make their way to disk. Calling DB.Close() multiple times is not safe and would
// cause panic.
func (db *DB) Close() (err error) {
db.elog.Printf("Closing database")
// Stop value GC first.
db.closers.valueGC.SignalAndWait()
// Stop writes next.
db.closers.writes.SignalAndWait()
// Now close the value log.
if vlogErr := db.vlog.Close(); err == nil {
err = errors.Wrap(vlogErr, "DB.Close")
}
// Make sure that block writer is done pushing stuff into memtable!
// Otherwise, you will have a race condition: we are trying to flush memtables
// and remove them completely, while the block / memtable writer is still
// trying to push stuff into the memtable. This will also resolve the value
// offset problem: as we push into memtable, we update value offsets there.
if !db.mt.Empty() {
db.elog.Printf("Flushing memtable")
for {
pushedFlushTask := func() bool {
db.Lock()
defer db.Unlock()
y.AssertTrue(db.mt != nil)
select {
case db.flushChan <- flushTask{db.mt, db.vptr}:
db.imm = append(db.imm, db.mt) // Flusher will attempt to remove this from s.imm.
db.mt = nil // Will segfault if we try writing!
db.elog.Printf("pushed to flush chan\n")
return true
default:
// If we fail to push, we need to unlock and wait for a short while.
// The flushing operation needs to update s.imm. Otherwise, we have a deadlock.
// TODO: Think about how to do this more cleanly, maybe without any locks.
}
return false
}()
if pushedFlushTask {
break
}
time.Sleep(10 * time.Millisecond)
}
}
db.flushChan <- flushTask{nil, valuePointer{}} // Tell flusher to quit.
if db.closers.memtable != nil {
db.closers.memtable.Wait()
db.elog.Printf("Memtable flushed")
}
if db.closers.compactors != nil {
db.closers.compactors.SignalAndWait()
db.elog.Printf("Compaction finished")
}
// Force Compact L0
// We don't need to care about cstatus since no parallel compaction is running.
cd := compactDef{
elog: trace.New("Badger", "Compact"),
thisLevel: db.lc.levels[0],
nextLevel: db.lc.levels[1],
}
cd.elog.SetMaxEvents(100)
defer cd.elog.Finish()
if db.lc.fillTablesL0(&cd) {
if err := db.lc.runCompactDef(0, cd); err != nil {
cd.elog.LazyPrintf("\tLOG Compact FAILED with error: %+v: %+v", err, cd)
}
} else {
cd.elog.LazyPrintf("fillTables failed for level zero. No compaction required")
}
if lcErr := db.lc.close(); err == nil {
err = errors.Wrap(lcErr, "DB.Close")
}
db.elog.Printf("Waiting for closer")
db.closers.updateSize.SignalAndWait()
db.elog.Finish()
if db.dirLockGuard != nil {
if guardErr := db.dirLockGuard.release(); err == nil {
err = errors.Wrap(guardErr, "DB.Close")
}
}
if db.valueDirGuard != nil {
if guardErr := db.valueDirGuard.release(); err == nil {
err = errors.Wrap(guardErr, "DB.Close")
}
}
if manifestErr := db.manifest.close(); err == nil {
err = errors.Wrap(manifestErr, "DB.Close")
}
// Fsync directories to ensure that lock file, and any other removed files whose directory
// we haven't specifically fsynced, are guaranteed to have their directory entry removal
// persisted to disk.
if syncErr := syncDir(db.opt.Dir); err == nil {
err = errors.Wrap(syncErr, "DB.Close")
}
if syncErr := syncDir(db.opt.ValueDir); err == nil {
err = errors.Wrap(syncErr, "DB.Close")
}
return err
}
const (
lockFile = "LOCK"
)
// When you create or delete a file, you have to ensure the directory entry for the file is synced
// in order to guarantee the file is visible (if the system crashes). (See the man page for fsync,
// or see https://github.com/coreos/etcd/issues/6368 for an example.)
func syncDir(dir string) error {
f, err := openDir(dir)
if err != nil {
return errors.Wrapf(err, "While opening directory: %s.", dir)
}
err = f.Sync()
closeErr := f.Close()
if err != nil {
return errors.Wrapf(err, "While syncing directory: %s.", dir)
}
return errors.Wrapf(closeErr, "While closing directory: %s.", dir)
}
// getMemtables returns the current memtables and get references.
func (db *DB) getMemTables() ([]*skl.Skiplist, func()) {
db.RLock()
defer db.RUnlock()
tables := make([]*skl.Skiplist, len(db.imm)+1)
// Get mutable memtable.
tables[0] = db.mt
tables[0].IncrRef()
// Get immutable memtables.
last := len(db.imm) - 1
for i := range db.imm {
tables[i+1] = db.imm[last-i]
tables[i+1].IncrRef()
}
return tables, func() {
for _, tbl := range tables {
tbl.DecrRef()
}
}
}
// get returns the value in memtable or disk for given key.
// Note that value will include meta byte.
//
// IMPORTANT: We should never write an entry with an older timestamp for the same key, We need to
// maintain this invariant to search for the latest value of a key, or else we need to search in all
// tables and find the max version among them. To maintain this invariant, we also need to ensure
// that all versions of a key are always present in the same table from level 1, because compaction
// can push any table down.
func (db *DB) get(key []byte) (y.ValueStruct, error) {
tables, decr := db.getMemTables() // Lock should be released.
defer decr()
y.NumGets.Add(1)
for i := 0; i < len(tables); i++ {
vs := tables[i].Get(key)
y.NumMemtableGets.Add(1)
if vs.Meta != 0 || vs.Value != nil {
return vs, nil
}
}
return db.lc.get(key)
}
func (db *DB) updateOffset(ptrs []valuePointer) {
var ptr valuePointer
for i := len(ptrs) - 1; i >= 0; i-- {
p := ptrs[i]
if !p.IsZero() {
ptr = p
break
}
}
if ptr.IsZero() {
return
}
db.Lock()
defer db.Unlock()
y.AssertTrue(!ptr.Less(db.vptr))
db.vptr = ptr
}
var requestPool = sync.Pool{
New: func() interface{} {
return new(request)
},
}
func (db *DB) shouldWriteValueToLSM(e Entry) bool {
return len(e.Value) < db.opt.ValueThreshold
}
func (db *DB) writeToLSM(b *request) error {
if len(b.Ptrs) != len(b.Entries) {
return errors.Errorf("Ptrs and Entries don't match: %+v", b)
}
for i, entry := range b.Entries {
if entry.meta&bitFinTxn != 0 {
continue
}
if db.shouldWriteValueToLSM(*entry) { // Will include deletion / tombstone case.
db.mt.Put(entry.Key,
y.ValueStruct{
Value: entry.Value,
Meta: entry.meta,
UserMeta: entry.UserMeta,
ExpiresAt: entry.ExpiresAt,
})
} else {
var offsetBuf [vptrSize]byte
db.mt.Put(entry.Key,
y.ValueStruct{
Value: b.Ptrs[i].Encode(offsetBuf[:]),
Meta: entry.meta | bitValuePointer,
UserMeta: entry.UserMeta,
ExpiresAt: entry.ExpiresAt,
})
}
}
return nil
}
// writeRequests is called serially by only one goroutine.
func (db *DB) writeRequests(reqs []*request) error {
if len(reqs) == 0 {
return nil
}
done := func(err error) {
for _, r := range reqs {
r.Err = err
r.Wg.Done()
}
}
db.elog.Printf("writeRequests called. Writing to value log")
err := db.vlog.write(reqs)
if err != nil {
done(err)
return err
}
db.elog.Printf("Writing to memtable")
var count int
for _, b := range reqs {
if len(b.Entries) == 0 {
continue
}
count += len(b.Entries)
var i uint64
for err := db.ensureRoomForWrite(); err == errNoRoom; err = db.ensureRoomForWrite() {
i++
if i%100 == 0 {
db.elog.Printf("Making room for writes")
}
// We need to poll a bit because both hasRoomForWrite and the flusher need access to s.imm.
// When flushChan is full and you are blocked there, and the flusher is trying to update s.imm,
// you will get a deadlock.
time.Sleep(10 * time.Millisecond)
}
if err != nil {
done(err)
return errors.Wrap(err, "writeRequests")
}
if err := db.writeToLSM(b); err != nil {
done(err)
return errors.Wrap(err, "writeRequests")
}
db.updateOffset(b.Ptrs)
}
done(nil)
db.elog.Printf("%d entries written", count)
return nil
}
func (db *DB) sendToWriteCh(entries []*Entry) (*request, error) {
var count, size int64
for _, e := range entries {
size += int64(e.estimateSize(db.opt.ValueThreshold))
count++
}
if count >= db.opt.maxBatchCount || size >= db.opt.maxBatchSize {
return nil, ErrTxnTooBig
}
// We can only service one request because we need each txn to be stored in a contigous section.
// Txns should not interleave among other txns or rewrites.
req := requestPool.Get().(*request)
req.Entries = entries
req.Wg = sync.WaitGroup{}
req.Wg.Add(1)
db.writeCh <- req // Handled in doWrites.
y.NumPuts.Add(int64(len(entries)))
return req, nil
}
func (db *DB) doWrites(lc *y.Closer) {
defer lc.Done()
pendingCh := make(chan struct{}, 1)
writeRequests := func(reqs []*request) {
if err := db.writeRequests(reqs); err != nil {
log.Printf("ERROR in Badger::writeRequests: %v", err)
}
<-pendingCh
}
// This variable tracks the number of pending writes.
reqLen := new(expvar.Int)
y.PendingWrites.Set(db.opt.Dir, reqLen)
reqs := make([]*request, 0, 10)
for {
var r *request
select {
case r = <-db.writeCh:
case <-lc.HasBeenClosed():
goto closedCase
}
for {
reqs = append(reqs, r)
reqLen.Set(int64(len(reqs)))
if len(reqs) >= 3*kvWriteChCapacity {
pendingCh <- struct{}{} // blocking.
goto writeCase
}
select {
// Either push to pending, or continue to pick from writeCh.
case r = <-db.writeCh:
case pendingCh <- struct{}{}:
goto writeCase
case <-lc.HasBeenClosed():
goto closedCase
}
}
closedCase:
close(db.writeCh)
for r := range db.writeCh { // Flush the channel.
reqs = append(reqs, r)
}
pendingCh <- struct{}{} // Push to pending before doing a write.
writeRequests(reqs)
return
writeCase:
go writeRequests(reqs)
reqs = make([]*request, 0, 10)
reqLen.Set(0)
}
}
// batchSet applies a list of badger.Entry. If a request level error occurs it
// will be returned.
// Check(kv.BatchSet(entries))
func (db *DB) batchSet(entries []*Entry) error {
req, err := db.sendToWriteCh(entries)
if err != nil {
return err
}
return req.Wait()
}
// batchSetAsync is the asynchronous version of batchSet. It accepts a callback
// function which is called when all the sets are complete. If a request level
// error occurs, it will be passed back via the callback.
// err := kv.BatchSetAsync(entries, func(err error)) {
// Check(err)
// }
func (db *DB) batchSetAsync(entries []*Entry, f func(error)) error {
req, err := db.sendToWriteCh(entries)
if err != nil {
return err
}
go func() {
err := req.Wait()
// Write is complete. Let's call the callback function now.
f(err)
}()
return nil
}
var errNoRoom = errors.New("No room for write")
// ensureRoomForWrite is always called serially.
func (db *DB) ensureRoomForWrite() error {
var err error
db.Lock()
defer db.Unlock()
if db.mt.MemSize() < db.opt.MaxTableSize {
return nil
}
y.AssertTrue(db.mt != nil) // A nil mt indicates that DB is being closed.
select {
case db.flushChan <- flushTask{db.mt, db.vptr}:
db.elog.Printf("Flushing value log to disk if async mode.")
// Ensure value log is synced to disk so this memtable's contents wouldn't be lost.
err = db.vlog.sync()
if err != nil {
return err
}
db.elog.Printf("Flushing memtable, mt.size=%d size of flushChan: %d\n",
db.mt.MemSize(), len(db.flushChan))
// We manage to push this task. Let's modify imm.
db.imm = append(db.imm, db.mt)
db.mt = skl.NewSkiplist(arenaSize(db.opt))
// New memtable is empty. We certainly have room.
return nil
default:
// We need to do this to unlock and allow the flusher to modify imm.
return errNoRoom
}
}
func arenaSize(opt Options) int64 {
return opt.MaxTableSize + opt.maxBatchSize + opt.maxBatchCount*int64(skl.MaxNodeSize)
}
// WriteLevel0Table flushes memtable.
func writeLevel0Table(s *skl.Skiplist, f *os.File) error {
iter := s.NewIterator()
defer iter.Close()
b := table.NewTableBuilder()
defer b.Close()
for iter.SeekToFirst(); iter.Valid(); iter.Next() {
if err := b.Add(iter.Key(), iter.Value()); err != nil {
return err
}
}
_, err := f.Write(b.Finish())
return err
}
type flushTask struct {
mt *skl.Skiplist
vptr valuePointer
}
// TODO: Ensure that this function doesn't return, or is handled by another wrapper function.
// Otherwise, we would have no goroutine which can flush memtables.
func (db *DB) flushMemtable(lc *y.Closer) error {
defer lc.Done()
for ft := range db.flushChan {
if ft.mt == nil {
return nil
}
if !ft.mt.Empty() {
// Store badger head even if vptr is zero, need it for readTs
db.elog.Printf("Storing offset: %+v\n", ft.vptr)
offset := make([]byte, vptrSize)
ft.vptr.Encode(offset)
// Pick the max commit ts, so in case of crash, our read ts would be higher than all the
// commits.
headTs := y.KeyWithTs(head, db.orc.commitTs())
ft.mt.Put(headTs, y.ValueStruct{Value: offset})
}
fileID := db.lc.reserveFileID()
fd, err := y.CreateSyncedFile(table.NewFilename(fileID, db.opt.Dir), true)
if err != nil {
return y.Wrap(err)
}
// Don't block just to sync the directory entry.
dirSyncCh := make(chan error)
go func() { dirSyncCh <- syncDir(db.opt.Dir) }()
err = writeLevel0Table(ft.mt, fd)
dirSyncErr := <-dirSyncCh
if err != nil {
db.elog.Errorf("ERROR while writing to level 0: %v", err)
return err
}
if dirSyncErr != nil {
db.elog.Errorf("ERROR while syncing level directory: %v", dirSyncErr)
return err
}
tbl, err := table.OpenTable(fd, db.opt.TableLoadingMode)
if err != nil {
db.elog.Printf("ERROR while opening table: %v", err)
return err
}
// We own a ref on tbl.
err = db.lc.addLevel0Table(tbl) // This will incrRef (if we don't error, sure)
tbl.DecrRef() // Releases our ref.
if err != nil {
return err
}
// Update s.imm. Need a lock.
db.Lock()
y.AssertTrue(ft.mt == db.imm[0]) //For now, single threaded.
db.imm = db.imm[1:]
ft.mt.DecrRef() // Return memory.
db.Unlock()
}
return nil
}
func exists(path string) (bool, error) {
_, err := os.Stat(path)
if err == nil {
return true, nil
}
if os.IsNotExist(err) {
return false, nil
}
return true, err
}
// This function does a filewalk, calculates the size of vlog and sst files and stores it in
// y.LSMSize and y.VlogSize.
func (db *DB) calculateSize() {
newInt := func(val int64) *expvar.Int {
v := new(expvar.Int)
v.Add(val)
return v
}
totalSize := func(dir string) (int64, int64) {
var lsmSize, vlogSize int64
err := filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
if err != nil {
return err
}
ext := filepath.Ext(path)
if ext == ".sst" {
lsmSize += info.Size()
} else if ext == ".vlog" {
vlogSize += info.Size()
}
return nil
})
if err != nil {
db.elog.Printf("Got error while calculating total size of directory: %s", dir)
}
return lsmSize, vlogSize
}
lsmSize, vlogSize := totalSize(db.opt.Dir)
y.LSMSize.Set(db.opt.Dir, newInt(lsmSize))
// If valueDir is different from dir, we'd have to do another walk.
if db.opt.ValueDir != db.opt.Dir {
_, vlogSize = totalSize(db.opt.ValueDir)
}
y.VlogSize.Set(db.opt.Dir, newInt(vlogSize))
}
func (db *DB) updateSize(lc *y.Closer) {
defer lc.Done()
metricsTicker := time.NewTicker(time.Minute)
defer metricsTicker.Stop()
for {
select {
case <-metricsTicker.C:
db.calculateSize()
case <-lc.HasBeenClosed():
return
}
}
}
// RunValueLogGC triggers a value log garbage collection.
//
// It picks value log files to perform GC based on statistics that are collected
// duing compactions. If no such statistics are available, then log files are
// picked in random order. The process stops as soon as the first log file is
// encountered which does not result in garbage collection.
//
// When a log file is picked, it is first sampled. If the sample shows that we
// can discard at least discardRatio space of that file, it would be rewritten.
//
// If a call to RunValueLogGC results in no rewrites, then an ErrNoRewrite is
// thrown indicating that the call resulted in no file rewrites.
//
// We recommend setting discardRatio to 0.5, thus indicating that a file be
// rewritten if half the space can be discarded. This results in a lifetime
// value log write amplification of 2 (1 from original write + 0.5 rewrite +
// 0.25 + 0.125 + ... = 2). Setting it to higher value would result in fewer
// space reclaims, while setting it to a lower value would result in more space
// reclaims at the cost of increased activity on the LSM tree. discardRatio
// must be in the range (0.0, 1.0), both endpoints excluded, otherwise an
// ErrInvalidRequest is returned.
//
// Only one GC is allowed at a time. If another value log GC is running, or DB
// has been closed, this would return an ErrRejected.
//
// Note: Every time GC is run, it would produce a spike of activity on the LSM
// tree.
func (db *DB) RunValueLogGC(discardRatio float64) error {
if discardRatio >= 1.0 || discardRatio <= 0.0 {
return ErrInvalidRequest
}
// Find head on disk
headKey := y.KeyWithTs(head, math.MaxUint64)
// Need to pass with timestamp, lsm get removes the last 8 bytes and compares key
val, err := db.lc.get(headKey)
if err != nil {
return errors.Wrap(err, "Retrieving head from on-disk LSM")
}
var head valuePointer
if len(val.Value) > 0 {
head.Decode(val.Value)
}
// Pick a log file and run GC
return db.vlog.runGC(discardRatio, head)
}
// Size returns the size of lsm and value log files in bytes. It can be used to decide how often to
// call RunValueLogGC.
func (db *DB) Size() (lsm int64, vlog int64) {
if y.LSMSize.Get(db.opt.Dir) == nil {
lsm, vlog = 0, 0
return
}
lsm = y.LSMSize.Get(db.opt.Dir).(*expvar.Int).Value()
vlog = y.VlogSize.Get(db.opt.Dir).(*expvar.Int).Value()
return
}
// Sequence represents a Badger sequence.
type Sequence struct {
sync.Mutex
db *DB
key []byte
next uint64
leased uint64
bandwidth uint64
}
// Next would return the next integer in the sequence, updating the lease by running a transaction
// if needed.
func (seq *Sequence) Next() (uint64, error) {