syncthing/lib/db/backend/leveldb_open.go

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// Copyright (C) 2018 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.
package backend
import (
"fmt"
"os"
"strconv"
"strings"
"github.com/syndtr/goleveldb/leveldb"
"github.com/syndtr/goleveldb/leveldb/errors"
"github.com/syndtr/goleveldb/leveldb/opt"
"github.com/syndtr/goleveldb/leveldb/storage"
"github.com/syndtr/goleveldb/leveldb/util"
)
const (
dbMaxOpenFiles = 100
// A large database is > 200 MiB. It's a mostly arbitrary value, but
// it's also the case that each file is 2 MiB by default and when we
// have dbMaxOpenFiles of them we will need to start thrashing fd:s.
// Switching to large database settings causes larger files to be used
// when compacting, reducing the number.
dbLargeThreshold = dbMaxOpenFiles * (2 << MiB)
KiB = 10
MiB = 20
)
// OpenLevelDB attempts to open the database at the given location, and runs
// recovery on it if opening fails. Worst case, if recovery is not possible,
// the database is erased and created from scratch.
func OpenLevelDB(location string, tuning Tuning) (Backend, error) {
opts := optsFor(location, tuning)
ldb, err := open(location, opts)
if err != nil {
return nil, err
}
return newLeveldbBackend(ldb, location), nil
}
// OpenLevelDBAuto is OpenLevelDB with TuningAuto tuning.
func OpenLevelDBAuto(location string) (Backend, error) {
return OpenLevelDB(location, TuningAuto)
}
// OpenLevelDBRO attempts to open the database at the given location, read
// only.
func OpenLevelDBRO(location string) (Backend, error) {
opts := &opt.Options{
OpenFilesCacheCapacity: dbMaxOpenFiles,
ReadOnly: true,
}
ldb, err := open(location, opts)
if err != nil {
return nil, err
}
return newLeveldbBackend(ldb, location), nil
}
// OpenMemory returns a new Backend referencing an in-memory database.
func OpenLevelDBMemory() Backend {
ldb, _ := leveldb.Open(storage.NewMemStorage(), nil)
return newLeveldbBackend(ldb, "")
}
// optsFor returns the database options to use when opening a database with
// the given location and tuning. Settings can be overridden by debug
// environment variables.
func optsFor(location string, tuning Tuning) *opt.Options {
large := false
switch tuning {
case TuningLarge:
large = true
case TuningAuto:
large = dbIsLarge(location)
}
var (
// Set defaults used for small databases.
defaultBlockCacheCapacity = 0 // 0 means let leveldb use default
defaultBlockSize = 0
defaultCompactionTableSize = 0
defaultCompactionTableSizeMultiplier = 0
defaultWriteBuffer = 16 << MiB // increased from leveldb default of 4 MiB
defaultCompactionL0Trigger = opt.DefaultCompactionL0Trigger // explicit because we use it as base for other stuff
)
if large {
// Change the parameters for better throughput at the price of some
// RAM and larger files. This results in larger batches of writes
// and compaction at a lower frequency.
l.Infoln("Using large-database tuning")
defaultBlockCacheCapacity = 64 << MiB
defaultBlockSize = 64 << KiB
defaultCompactionTableSize = 16 << MiB
defaultCompactionTableSizeMultiplier = 20 // 2.0 after division by ten
defaultWriteBuffer = 64 << MiB
defaultCompactionL0Trigger = 8 // number of l0 files
}
opts := &opt.Options{
BlockCacheCapacity: debugEnvValue("BlockCacheCapacity", defaultBlockCacheCapacity),
BlockCacheEvictRemoved: debugEnvValue("BlockCacheEvictRemoved", 0) != 0,
BlockRestartInterval: debugEnvValue("BlockRestartInterval", 0),
BlockSize: debugEnvValue("BlockSize", defaultBlockSize),
CompactionExpandLimitFactor: debugEnvValue("CompactionExpandLimitFactor", 0),
CompactionGPOverlapsFactor: debugEnvValue("CompactionGPOverlapsFactor", 0),
CompactionL0Trigger: debugEnvValue("CompactionL0Trigger", defaultCompactionL0Trigger),
CompactionSourceLimitFactor: debugEnvValue("CompactionSourceLimitFactor", 0),
CompactionTableSize: debugEnvValue("CompactionTableSize", defaultCompactionTableSize),
CompactionTableSizeMultiplier: float64(debugEnvValue("CompactionTableSizeMultiplier", defaultCompactionTableSizeMultiplier)) / 10.0,
CompactionTotalSize: debugEnvValue("CompactionTotalSize", 0),
CompactionTotalSizeMultiplier: float64(debugEnvValue("CompactionTotalSizeMultiplier", 0)) / 10.0,
DisableBufferPool: debugEnvValue("DisableBufferPool", 0) != 0,
DisableBlockCache: debugEnvValue("DisableBlockCache", 0) != 0,
DisableCompactionBackoff: debugEnvValue("DisableCompactionBackoff", 0) != 0,
DisableLargeBatchTransaction: debugEnvValue("DisableLargeBatchTransaction", 0) != 0,
NoSync: debugEnvValue("NoSync", 0) != 0,
NoWriteMerge: debugEnvValue("NoWriteMerge", 0) != 0,
OpenFilesCacheCapacity: debugEnvValue("OpenFilesCacheCapacity", dbMaxOpenFiles),
WriteBuffer: debugEnvValue("WriteBuffer", defaultWriteBuffer),
// The write slowdown and pause can be overridden, but even if they
// are not and the compaction trigger is overridden we need to
// adjust so that we don't pause writes for L0 compaction before we
// even *start* L0 compaction...
WriteL0SlowdownTrigger: debugEnvValue("WriteL0SlowdownTrigger", 2*debugEnvValue("CompactionL0Trigger", defaultCompactionL0Trigger)),
WriteL0PauseTrigger: debugEnvValue("WriteL0SlowdownTrigger", 3*debugEnvValue("CompactionL0Trigger", defaultCompactionL0Trigger)),
}
return opts
}
func open(location string, opts *opt.Options) (*leveldb.DB, error) {
db, err := leveldb.OpenFile(location, opts)
if leveldbIsCorrupted(err) {
db, err = leveldb.RecoverFile(location, opts)
}
if leveldbIsCorrupted(err) {
// The database is corrupted, and we've tried to recover it but it
// didn't work. At this point there isn't much to do beyond dropping
// the database and reindexing...
l.Infoln("Database corruption detected, unable to recover. Reinitializing...")
if err := os.RemoveAll(location); err != nil {
return nil, &errorSuggestion{err, "failed to delete corrupted database"}
}
db, err = leveldb.OpenFile(location, opts)
}
if err != nil {
return nil, &errorSuggestion{err, "is another instance of Syncthing running?"}
}
if debugEnvValue("CompactEverything", 0) != 0 {
if err := db.CompactRange(util.Range{}); err != nil {
l.Warnln("Compacting database:", err)
}
}
return db, nil
}
func debugEnvValue(key string, def int) int {
v, err := strconv.ParseInt(os.Getenv("STDEBUG_"+key), 10, 63)
if err != nil {
return def
}
return int(v)
}
// A "better" version of leveldb's errors.IsCorrupted.
func leveldbIsCorrupted(err error) bool {
switch {
case err == nil:
return false
case errors.IsCorrupted(err):
return true
case strings.Contains(err.Error(), "corrupted"):
return true
}
return false
}
// dbIsLarge returns whether the estimated size of the database at location
// is large enough to warrant optimization for large databases.
func dbIsLarge(location string) bool {
if ^uint(0)>>63 == 0 {
// We're compiled for a 32 bit architecture. We've seen trouble with
// large settings there.
// (https://forum.syncthing.net/t/many-small-ldb-files-with-database-tuning/13842)
return false
}
entries, err := os.ReadDir(location)
if err != nil {
return false
}
var size int64
for _, entry := range entries {
if entry.Name() == "LOG" {
// don't count the size
continue
}
fi, err := entry.Info()
if err != nil {
continue
}
size += fi.Size()
}
return size > dbLargeThreshold
}
type errorSuggestion struct {
inner error
suggestion string
}
func (e *errorSuggestion) Error() string {
return fmt.Sprintf("%s (%s)", e.inner.Error(), e.suggestion)
}