lnd.xprv/channeldb/kvdb/backend.go
2020-11-13 10:19:51 +01:00

249 lines
8.0 KiB
Go

package kvdb
import (
"encoding/binary"
"fmt"
"io/ioutil"
"os"
"path/filepath"
"time"
_ "github.com/btcsuite/btcwallet/walletdb/bdb" // Import to register backend.
)
const (
// DefaultTempDBFileName is the default name of the temporary bolt DB
// file that we'll use to atomically compact the primary DB file on
// startup.
DefaultTempDBFileName = "temp-dont-use.db"
// LastCompactionFileNameSuffix is the suffix we append to the file name
// of a database file to record the timestamp when the last compaction
// occurred.
LastCompactionFileNameSuffix = ".last-compacted"
)
var (
byteOrder = binary.BigEndian
)
// fileExists returns true if the file exists, and false otherwise.
func fileExists(path string) bool {
if _, err := os.Stat(path); err != nil {
if os.IsNotExist(err) {
return false
}
}
return true
}
// BoltBackendConfig is a struct that holds settings specific to the bolt
// database backend.
type BoltBackendConfig struct {
// DBPath is the directory path in which the database file should be
// stored.
DBPath string
// DBFileName is the name of the database file.
DBFileName string
// NoFreelistSync, if true, prevents the database from syncing its
// freelist to disk, resulting in improved performance at the expense of
// increased startup time.
NoFreelistSync bool
// AutoCompact specifies if a Bolt based database backend should be
// automatically compacted on startup (if the minimum age of the
// database file is reached). This will require additional disk space
// for the compacted copy of the database but will result in an overall
// lower database size after the compaction.
AutoCompact bool
// AutoCompactMinAge specifies the minimum time that must have passed
// since a bolt database file was last compacted for the compaction to
// be considered again.
AutoCompactMinAge time.Duration
}
// GetBoltBackend opens (or creates if doesn't exits) a bbolt backed database
// and returns a kvdb.Backend wrapping it.
func GetBoltBackend(cfg *BoltBackendConfig) (Backend, error) {
dbFilePath := filepath.Join(cfg.DBPath, cfg.DBFileName)
// Is this a new database?
if !fileExists(dbFilePath) {
if !fileExists(cfg.DBPath) {
if err := os.MkdirAll(cfg.DBPath, 0700); err != nil {
return nil, err
}
}
return Create(BoltBackendName, dbFilePath, cfg.NoFreelistSync)
}
// This is an existing database. We might want to compact it on startup
// to free up some space.
if cfg.AutoCompact {
if err := compactAndSwap(cfg); err != nil {
return nil, err
}
}
return Open(BoltBackendName, dbFilePath, cfg.NoFreelistSync)
}
// compactAndSwap will attempt to write a new temporary DB file to disk with
// the compacted database content, then atomically swap (via rename) the old
// file for the new file by updating the name of the new file to the old.
func compactAndSwap(cfg *BoltBackendConfig) error {
sourceName := cfg.DBFileName
// If the main DB file isn't set, then we can't proceed.
if sourceName == "" {
return fmt.Errorf("cannot compact DB with empty name")
}
sourceFilePath := filepath.Join(cfg.DBPath, sourceName)
tempDestFilePath := filepath.Join(cfg.DBPath, DefaultTempDBFileName)
// Let's find out how long ago the last compaction of the source file
// occurred and possibly skip compacting it again now.
lastCompactionDate, err := lastCompactionDate(sourceFilePath)
if err != nil {
return fmt.Errorf("cannot determine last compaction date of "+
"source DB file: %v", err)
}
compactAge := time.Since(lastCompactionDate)
if cfg.AutoCompactMinAge != 0 && compactAge <= cfg.AutoCompactMinAge {
log.Infof("Not compacting database file at %v, it was last "+
"compacted at %v (%v ago), min age is set to %v",
sourceFilePath, lastCompactionDate,
compactAge.Truncate(time.Second), cfg.AutoCompactMinAge)
return nil
}
log.Infof("Compacting database file at %v", sourceFilePath)
// If the old temporary DB file still exists, then we'll delete it
// before proceeding.
if _, err := os.Stat(tempDestFilePath); err == nil {
log.Infof("Found old temp DB @ %v, removing before swap",
tempDestFilePath)
err = os.Remove(tempDestFilePath)
if err != nil {
return fmt.Errorf("unable to remove old temp DB file: "+
"%v", err)
}
}
// Now that we know the staging area is clear, we'll create the new
// temporary DB file and close it before we write the new DB to it.
tempFile, err := os.Create(tempDestFilePath)
if err != nil {
return fmt.Errorf("unable to create temp DB file: %v", err)
}
if err := tempFile.Close(); err != nil {
return fmt.Errorf("unable to close file: %v", err)
}
// With the file created, we'll start the compaction and remove the
// temporary file all together once this method exits.
defer func() {
// This will only succeed if the rename below fails. If the
// compaction is successful, the file won't exist on exit
// anymore so no need to log an error here.
_ = os.Remove(tempDestFilePath)
}()
c := &compacter{
srcPath: sourceFilePath,
dstPath: tempDestFilePath,
}
initialSize, newSize, err := c.execute()
if err != nil {
return fmt.Errorf("error during compact: %v", err)
}
log.Infof("DB compaction of %v successful, %d -> %d bytes (gain=%.2fx)",
sourceFilePath, initialSize, newSize,
float64(initialSize)/float64(newSize))
// We try to store the current timestamp in a file with the suffix
// .last-compacted so we can figure out how long ago the last compaction
// was. But since this shouldn't fail the compaction process itself, we
// only log the error. Worst case if this file cannot be written is that
// we compact on every startup.
err = updateLastCompactionDate(sourceFilePath)
if err != nil {
log.Warnf("Could not update last compaction timestamp in "+
"%s%s: %v", sourceFilePath,
LastCompactionFileNameSuffix, err)
}
log.Infof("Swapping old DB file from %v to %v", tempDestFilePath,
sourceFilePath)
// Finally, we'll attempt to atomically rename the temporary file to
// the main back up file. If this succeeds, then we'll only have a
// single file on disk once this method exits.
return os.Rename(tempDestFilePath, sourceFilePath)
}
// lastCompactionDate returns the date the given database file was last
// compacted or a zero time.Time if no compaction was recorded before. The
// compaction date is read from a file in the same directory and with the same
// name as the DB file, but with the suffix ".last-compacted".
func lastCompactionDate(dbFile string) (time.Time, error) {
zeroTime := time.Unix(0, 0)
tsFile := fmt.Sprintf("%s%s", dbFile, LastCompactionFileNameSuffix)
if !fileExists(tsFile) {
return zeroTime, nil
}
tsBytes, err := ioutil.ReadFile(tsFile)
if err != nil {
return zeroTime, err
}
tsNano := byteOrder.Uint64(tsBytes)
return time.Unix(0, int64(tsNano)), nil
}
// updateLastCompactionDate stores the current time as a timestamp in a file
// in the same directory and with the same name as the DB file, but with the
// suffix ".last-compacted".
func updateLastCompactionDate(dbFile string) error {
var tsBytes [8]byte
byteOrder.PutUint64(tsBytes[:], uint64(time.Now().UnixNano()))
tsFile := fmt.Sprintf("%s%s", dbFile, LastCompactionFileNameSuffix)
return ioutil.WriteFile(tsFile, tsBytes[:], 0600)
}
// GetTestBackend opens (or creates if doesn't exist) a bbolt or etcd
// backed database (for testing), and returns a kvdb.Backend and a cleanup
// func. Whether to create/open bbolt or embedded etcd database is based
// on the TestBackend constant which is conditionally compiled with build tag.
// The passed path is used to hold all db files, while the name is only used
// for bbolt.
func GetTestBackend(path, name string) (Backend, func(), error) {
empty := func() {}
if TestBackend == BoltBackendName {
db, err := GetBoltBackend(&BoltBackendConfig{
DBPath: path,
DBFileName: name,
NoFreelistSync: true,
})
if err != nil {
return nil, nil, err
}
return db, empty, nil
} else if TestBackend == EtcdBackendName {
return GetEtcdTestBackend(path, name)
}
return nil, nil, fmt.Errorf("unknown backend")
}