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// Copyright (c) 2016, Suryandaru Triandana <syndtr@gmail.com>
// All rights reserved.
//
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
package leveldb
import (
"errors"
"sync"
"time"
"github.com/syndtr/goleveldb/leveldb/iterator"
"github.com/syndtr/goleveldb/leveldb/opt"
"github.com/syndtr/goleveldb/leveldb/util"
)
var errTransactionDone = errors.New("leveldb: transaction already closed")
// Transaction is the transaction handle.
type Transaction struct {
db *DB
lk sync.RWMutex
seq uint64
mem *memDB
tables tFiles
ikScratch []byte
rec sessionRecord
stats cStatStaging
closed bool
}
// Get gets the value for the given key. It returns ErrNotFound if the
// DB does not contains the key.
//
// The returned slice is its own copy, it is safe to modify the contents
// of the returned slice.
// It is safe to modify the contents of the argument after Get returns.
func (tr *Transaction) Get(key []byte, ro *opt.ReadOptions) ([]byte, error) {
tr.lk.RLock()
defer tr.lk.RUnlock()
if tr.closed {
return nil, errTransactionDone
}
return tr.db.get(tr.mem.DB, tr.tables, key, tr.seq, ro)
}
// Has returns true if the DB does contains the given key.
//
// It is safe to modify the contents of the argument after Has returns.
func (tr *Transaction) Has(key []byte, ro *opt.ReadOptions) (bool, error) {
tr.lk.RLock()
defer tr.lk.RUnlock()
if tr.closed {
return false, errTransactionDone
}
return tr.db.has(tr.mem.DB, tr.tables, key, tr.seq, ro)
}
// NewIterator returns an iterator for the latest snapshot of the transaction.
// The returned iterator is not safe for concurrent use, but it is safe to use
// multiple iterators concurrently, with each in a dedicated goroutine.
// It is also safe to use an iterator concurrently while writes to the
// transaction. The resultant key/value pairs are guaranteed to be consistent.
//
// Slice allows slicing the iterator to only contains keys in the given
// range. A nil Range.Start is treated as a key before all keys in the
// DB. And a nil Range.Limit is treated as a key after all keys in
// the DB.
//
// WARNING: Any slice returned by interator (e.g. slice returned by calling
// Iterator.Key() or Iterator.Key() methods), its content should not be modified
// unless noted otherwise.
//
// The iterator must be released after use, by calling Release method.
//
// Also read Iterator documentation of the leveldb/iterator package.
func (tr *Transaction) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator {
tr.lk.RLock()
defer tr.lk.RUnlock()
if tr.closed {
return iterator.NewEmptyIterator(errTransactionDone)
}
tr.mem.incref()
return tr.db.newIterator(tr.mem, tr.tables, tr.seq, slice, ro)
}
func (tr *Transaction) flush() error {
// Flush memdb.
if tr.mem.Len() != 0 {
tr.stats.startTimer()
iter := tr.mem.NewIterator(nil)
t, n, err := tr.db.s.tops.createFrom(iter)
iter.Release()
tr.stats.stopTimer()
if err != nil {
return err
}
if tr.mem.getref() == 1 {
tr.mem.Reset()
} else {
tr.mem.decref()
tr.mem = tr.db.mpoolGet(0)
tr.mem.incref()
}
tr.tables = append(tr.tables, t)
tr.rec.addTableFile(0, t)
tr.stats.write += t.size
tr.db.logf("transaction@flush created L0@%d N·%d S·%s %q:%q", t.fd.Num, n, shortenb(int(t.size)), t.imin, t.imax)
}
return nil
}
func (tr *Transaction) put(kt keyType, key, value []byte) error {
tr.ikScratch = makeInternalKey(tr.ikScratch, key, tr.seq+1, kt)
if tr.mem.Free() < len(tr.ikScratch)+len(value) {
if err := tr.flush(); err != nil {
return err
}
}
if err := tr.mem.Put(tr.ikScratch, value); err != nil {
return err
}
tr.seq++
return nil
}
// Put sets the value for the given key. It overwrites any previous value
// for that key; a DB is not a multi-map.
// Please note that the transaction is not compacted until committed, so if you
// writes 10 same keys, then those 10 same keys are in the transaction.
//
// It is safe to modify the contents of the arguments after Put returns.
func (tr *Transaction) Put(key, value []byte, wo *opt.WriteOptions) error {
tr.lk.Lock()
defer tr.lk.Unlock()
if tr.closed {
return errTransactionDone
}
return tr.put(keyTypeVal, key, value)
}
// Delete deletes the value for the given key.
// Please note that the transaction is not compacted until committed, so if you
// writes 10 same keys, then those 10 same keys are in the transaction.
//
// It is safe to modify the contents of the arguments after Delete returns.
func (tr *Transaction) Delete(key []byte, wo *opt.WriteOptions) error {
tr.lk.Lock()
defer tr.lk.Unlock()
if tr.closed {
return errTransactionDone
}
return tr.put(keyTypeDel, key, nil)
}
// Write apply the given batch to the transaction. The batch will be applied
// sequentially.
// Please note that the transaction is not compacted until committed, so if you
// writes 10 same keys, then those 10 same keys are in the transaction.
//
// It is safe to modify the contents of the arguments after Write returns.
func (tr *Transaction) Write(b *Batch, wo *opt.WriteOptions) error {
if b == nil || b.Len() == 0 {
return nil
}
tr.lk.Lock()
defer tr.lk.Unlock()
if tr.closed {
return errTransactionDone
}
return b.replayInternal(func(i int, kt keyType, k, v []byte) error {
return tr.put(kt, k, v)
})
}
func (tr *Transaction) setDone() {
tr.closed = true
tr.db.tr = nil
tr.mem.decref()
<-tr.db.writeLockC
}
// Commit commits the transaction. If error is not nil, then the transaction is
// not committed, it can then either be retried or discarded.
//
// Other methods should not be called after transaction has been committed.
func (tr *Transaction) Commit() error {
if err := tr.db.ok(); err != nil {
return err
}
tr.lk.Lock()
defer tr.lk.Unlock()
if tr.closed {
return errTransactionDone
}
if err := tr.flush(); err != nil {
// Return error, lets user decide either to retry or discard
// transaction.
return err
}
if len(tr.tables) != 0 {
// Committing transaction.
tr.rec.setSeqNum(tr.seq)
tr.db.compCommitLk.Lock()
tr.stats.startTimer()
var cerr error
for retry := 0; retry < 3; retry++ {
cerr = tr.db.s.commit(&tr.rec, false)
if cerr != nil {
tr.db.logf("transaction@commit error R·%d %q", retry, cerr)
select {
case <-time.After(time.Second):
case <-tr.db.closeC:
tr.db.logf("transaction@commit exiting")
tr.db.compCommitLk.Unlock()
return cerr
}
} else {
// Success. Set db.seq.
tr.db.setSeq(tr.seq)
break
}
}
tr.stats.stopTimer()
if cerr != nil {
// Return error, lets user decide either to retry or discard
// transaction.
return cerr
}
// Update compaction stats. This is safe as long as we hold compCommitLk.
tr.db.compStats.addStat(0, &tr.stats)
// Trigger table auto-compaction.
tr.db.compTrigger(tr.db.tcompCmdC)
tr.db.compCommitLk.Unlock()
// Additionally, wait compaction when certain threshold reached.
// Ignore error, returns error only if transaction can't be committed.
tr.db.waitCompaction()
}
// Only mark as done if transaction committed successfully.
tr.setDone()
return nil
}
func (tr *Transaction) discard() {
// Discard transaction.
for _, t := range tr.tables {
tr.db.logf("transaction@discard @%d", t.fd.Num)
if err1 := tr.db.s.stor.Remove(t.fd); err1 == nil {
tr.db.s.reuseFileNum(t.fd.Num)
}
}
}
// Discard discards the transaction.
//
// Other methods should not be called after transaction has been discarded.
func (tr *Transaction) Discard() {
tr.lk.Lock()
if !tr.closed {
tr.discard()
tr.setDone()
}
tr.lk.Unlock()
}
func (db *DB) waitCompaction() error {
if db.s.tLen(0) >= db.s.o.GetWriteL0PauseTrigger() {
return db.compTriggerWait(db.tcompCmdC)
}
return nil
}
// OpenTransaction opens an atomic DB transaction. Only one transaction can be
// opened at a time. Subsequent call to Write and OpenTransaction will be blocked
// until in-flight transaction is committed or discarded.
// The returned transaction handle is safe for concurrent use.
//
// Transaction is expensive and can overwhelm compaction, especially if
// transaction size is small. Use with caution.
//
// The transaction must be closed once done, either by committing or discarding
// the transaction.
// Closing the DB will discard open transaction.
func (db *DB) OpenTransaction() (*Transaction, error) {
if err := db.ok(); err != nil {
return nil, err
}
// The write happen synchronously.
select {
case db.writeLockC <- struct{}{}:
case err := <-db.compPerErrC:
return nil, err
case <-db.closeC:
return nil, ErrClosed
}
if db.tr != nil {
panic("leveldb: has open transaction")
}
// Flush current memdb.
if db.mem != nil && db.mem.Len() != 0 {
if _, err := db.rotateMem(0, true); err != nil {
return nil, err
}
}
// Wait compaction when certain threshold reached.
if err := db.waitCompaction(); err != nil {
return nil, err
}
tr := &Transaction{
db: db,
seq: db.seq,
mem: db.mpoolGet(0),
}
tr.mem.incref()
db.tr = tr
return tr, nil
}
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