Merge pull request #3189 from fjl/leveldb-update

Update goleveldb, add debug.chaindbCompact

27 files changed, 806 insertions, 493 deletions

diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/batch.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/batch.go
index 501006717..225920002 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/batch.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/batch.go
@@ -9,13 +9,15 @@ package leveldb
 import (
 	"encoding/binary"
 	"fmt"
+	"io"
 
 	"github.com/syndtr/goleveldb/leveldb/errors"
 	"github.com/syndtr/goleveldb/leveldb/memdb"
 	"github.com/syndtr/goleveldb/leveldb/storage"
 )
 
-// ErrBatchCorrupted records reason of batch corruption.
+// ErrBatchCorrupted records reason of batch corruption. This error will be
+// wrapped with errors.ErrCorrupted.
 type ErrBatchCorrupted struct {
 	Reason string
 }
@@ -29,8 +31,9 @@ func newErrBatchCorrupted(reason string) error {
 }
 
 const (
-	batchHdrLen  = 8 + 4
-	batchGrowRec = 3000
+	batchHeaderLen = 8 + 4
+	batchGrowRec   = 3000
+	batchBufioSize = 16
 )
 
 // BatchReplay wraps basic batch operations.
@@ -39,34 +42,46 @@ type BatchReplay interface {
 	Delete(key []byte)
 }
 
+type batchIndex struct {
+	keyType            keyType
+	keyPos, keyLen     int
+	valuePos, valueLen int
+}
+
+func (index batchIndex) k(data []byte) []byte {
+	return data[index.keyPos : index.keyPos+index.keyLen]
+}
+
+func (index batchIndex) v(data []byte) []byte {
+	if index.valueLen != 0 {
+		return data[index.valuePos : index.valuePos+index.valueLen]
+	}
+	return nil
+}
+
+func (index batchIndex) kv(data []byte) (key, value []byte) {
+	return index.k(data), index.v(data)
+}
+
 // Batch is a write batch.
 type Batch struct {
-	data       []byte
-	rLen, bLen int
-	seq        uint64
-	sync       bool
+	data  []byte
+	index []batchIndex
+
+	// internalLen is sums of key/value pair length plus 8-bytes internal key.
+	internalLen int
 }
 
 func (b *Batch) grow(n int) {
-	off := len(b.data)
-	if off == 0 {
-		off = batchHdrLen
-		if b.data != nil {
-			b.data = b.data[:off]
-		}
-	}
-	if cap(b.data)-off < n {
-		if b.data == nil {
-			b.data = make([]byte, off, off+n)
-		} else {
-			odata := b.data
-			div := 1
-			if b.rLen > batchGrowRec {
-				div = b.rLen / batchGrowRec
-			}
-			b.data = make([]byte, off, off+n+(off-batchHdrLen)/div)
-			copy(b.data, odata)
+	o := len(b.data)
+	if cap(b.data)-o < n {
+		div := 1
+		if len(b.index) > batchGrowRec {
+			div = len(b.index) / batchGrowRec
 		}
+		ndata := make([]byte, o, o+n+o/div)
+		copy(ndata, b.data)
+		b.data = ndata
 	}
 }
 
@@ -76,32 +91,36 @@ func (b *Batch) appendRec(kt keyType, key, value []byte) {
 		n += binary.MaxVarintLen32 + len(value)
 	}
 	b.grow(n)
-	off := len(b.data)
-	data := b.data[:off+n]
-	data[off] = byte(kt)
-	off++
-	off += binary.PutUvarint(data[off:], uint64(len(key)))
-	copy(data[off:], key)
-	off += len(key)
+	index := batchIndex{keyType: kt}
+	o := len(b.data)
+	data := b.data[:o+n]
+	data[o] = byte(kt)
+	o++
+	o += binary.PutUvarint(data[o:], uint64(len(key)))
+	index.keyPos = o
+	index.keyLen = len(key)
+	o += copy(data[o:], key)
 	if kt == keyTypeVal {
-		off += binary.PutUvarint(data[off:], uint64(len(value)))
-		copy(data[off:], value)
-		off += len(value)
+		o += binary.PutUvarint(data[o:], uint64(len(value)))
+		index.valuePos = o
+		index.valueLen = len(value)
+		o += copy(data[o:], value)
 	}
-	b.data = data[:off]
-	b.rLen++
-	//  Include 8-byte ikey header
-	b.bLen += len(key) + len(value) + 8
+	b.data = data[:o]
+	b.index = append(b.index, index)
+	b.internalLen += index.keyLen + index.valueLen + 8
 }
 
 // Put appends 'put operation' of the given key/value pair to the batch.
-// It is safe to modify the contents of the argument after Put returns.
+// It is safe to modify the contents of the argument after Put returns but not
+// before.
 func (b *Batch) Put(key, value []byte) {
 	b.appendRec(keyTypeVal, key, value)
 }
 
 // Delete appends 'delete operation' of the given key to the batch.
-// It is safe to modify the contents of the argument after Delete returns.
+// It is safe to modify the contents of the argument after Delete returns but
+// not before.
 func (b *Batch) Delete(key []byte) {
 	b.appendRec(keyTypeDel, key, nil)
 }
@@ -111,7 +130,7 @@ func (b *Batch) Delete(key []byte) {
 // The returned slice is not its own copy, so the contents should not be
 // modified.
 func (b *Batch) Dump() []byte {
-	return b.encode()
+	return b.data
 }
 
 // Load loads given slice into the batch. Previous contents of the batch
@@ -119,144 +138,212 @@ func (b *Batch) Dump() []byte {
 // The given slice will not be copied and will be used as batch buffer, so
 // it is not safe to modify the contents of the slice.
 func (b *Batch) Load(data []byte) error {
-	return b.decode(0, data)
+	return b.decode(data, -1)
 }
 
 // Replay replays batch contents.
 func (b *Batch) Replay(r BatchReplay) error {
-	return b.decodeRec(func(i int, kt keyType, key, value []byte) error {
-		switch kt {
+	for _, index := range b.index {
+		switch index.keyType {
 		case keyTypeVal:
-			r.Put(key, value)
+			r.Put(index.k(b.data), index.v(b.data))
 		case keyTypeDel:
-			r.Delete(key)
+			r.Delete(index.k(b.data))
 		}
-		return nil
-	})
+	}
+	return nil
 }
 
 // Len returns number of records in the batch.
 func (b *Batch) Len() int {
-	return b.rLen
+	return len(b.index)
 }
 
 // Reset resets the batch.
 func (b *Batch) Reset() {
 	b.data = b.data[:0]
-	b.seq = 0
-	b.rLen = 0
-	b.bLen = 0
-	b.sync = false
+	b.index = b.index[:0]
+	b.internalLen = 0
 }
 
-func (b *Batch) init(sync bool) {
-	b.sync = sync
+func (b *Batch) replayInternal(fn func(i int, kt keyType, k, v []byte) error) error {
+	for i, index := range b.index {
+		if err := fn(i, index.keyType, index.k(b.data), index.v(b.data)); err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 func (b *Batch) append(p *Batch) {
-	if p.rLen > 0 {
-		b.grow(len(p.data) - batchHdrLen)
-		b.data = append(b.data, p.data[batchHdrLen:]...)
-		b.rLen += p.rLen
-		b.bLen += p.bLen
-	}
-	if p.sync {
-		b.sync = true
+	ob := len(b.data)
+	oi := len(b.index)
+	b.data = append(b.data, p.data...)
+	b.index = append(b.index, p.index...)
+	b.internalLen += p.internalLen
+
+	// Updating index offset.
+	if ob != 0 {
+		for ; oi < len(b.index); oi++ {
+			index := &b.index[oi]
+			index.keyPos += ob
+			if index.valueLen != 0 {
+				index.valuePos += ob
+			}
+		}
 	}
 }
 
-// size returns sums of key/value pair length plus 8-bytes ikey.
-func (b *Batch) size() int {
-	return b.bLen
-}
-
-func (b *Batch) encode() []byte {
-	b.grow(0)
-	binary.LittleEndian.PutUint64(b.data, b.seq)
-	binary.LittleEndian.PutUint32(b.data[8:], uint32(b.rLen))
-
-	return b.data
+func (b *Batch) decode(data []byte, expectedLen int) error {
+	b.data = data
+	b.index = b.index[:0]
+	b.internalLen = 0
+	err := decodeBatch(data, func(i int, index batchIndex) error {
+		b.index = append(b.index, index)
+		b.internalLen += index.keyLen + index.valueLen + 8
+		return nil
+	})
+	if err != nil {
+		return err
+	}
+	if expectedLen >= 0 && len(b.index) != expectedLen {
+		return newErrBatchCorrupted(fmt.Sprintf("invalid records length: %d vs %d", expectedLen, len(b.index)))
+	}
+	return nil
 }
 
-func (b *Batch) decode(prevSeq uint64, data []byte) error {
-	if len(data) < batchHdrLen {
-		return newErrBatchCorrupted("too short")
+func (b *Batch) putMem(seq uint64, mdb *memdb.DB) error {
+	var ik []byte
+	for i, index := range b.index {
+		ik = makeInternalKey(ik, index.k(b.data), seq+uint64(i), index.keyType)
+		if err := mdb.Put(ik, index.v(b.data)); err != nil {
+			return err
+		}
 	}
+	return nil
+}
 
-	b.seq = binary.LittleEndian.Uint64(data)
-	if b.seq < prevSeq {
-		return newErrBatchCorrupted("invalid sequence number")
-	}
-	b.rLen = int(binary.LittleEndian.Uint32(data[8:]))
-	if b.rLen < 0 {
-		return newErrBatchCorrupted("invalid records length")
+func (b *Batch) revertMem(seq uint64, mdb *memdb.DB) error {
+	var ik []byte
+	for i, index := range b.index {
+		ik = makeInternalKey(ik, index.k(b.data), seq+uint64(i), index.keyType)
+		if err := mdb.Delete(ik); err != nil {
+			return err
+		}
 	}
-	// No need to be precise at this point, it won't be used anyway
-	b.bLen = len(data) - batchHdrLen
-	b.data = data
-
 	return nil
 }
 
-func (b *Batch) decodeRec(f func(i int, kt keyType, key, value []byte) error) error {
-	off := batchHdrLen
-	for i := 0; i < b.rLen; i++ {
-		if off >= len(b.data) {
-			return newErrBatchCorrupted("invalid records length")
-		}
+func newBatch() interface{} {
+	return &Batch{}
+}
 
-		kt := keyType(b.data[off])
-		if kt > keyTypeVal {
-			panic(kt)
-			return newErrBatchCorrupted("bad record: invalid type")
+func decodeBatch(data []byte, fn func(i int, index batchIndex) error) error {
+	var index batchIndex
+	for i, o := 0, 0; o < len(data); i++ {
+		// Key type.
+		index.keyType = keyType(data[o])
+		if index.keyType > keyTypeVal {
+			return newErrBatchCorrupted(fmt.Sprintf("bad record: invalid type %#x", uint(index.keyType)))
 		}
-		off++
+		o++
 
-		x, n := binary.Uvarint(b.data[off:])
-		off += n
-		if n <= 0 || off+int(x) > len(b.data) {
+		// Key.
+		x, n := binary.Uvarint(data[o:])
+		o += n
+		if n <= 0 || o+int(x) > len(data) {
 			return newErrBatchCorrupted("bad record: invalid key length")
 		}
-		key := b.data[off : off+int(x)]
-		off += int(x)
-		var value []byte
-		if kt == keyTypeVal {
-			x, n := binary.Uvarint(b.data[off:])
-			off += n
-			if n <= 0 || off+int(x) > len(b.data) {
+		index.keyPos = o
+		index.keyLen = int(x)
+		o += index.keyLen
+
+		// Value.
+		if index.keyType == keyTypeVal {
+			x, n = binary.Uvarint(data[o:])
+			o += n
+			if n <= 0 || o+int(x) > len(data) {
 				return newErrBatchCorrupted("bad record: invalid value length")
 			}
-			value = b.data[off : off+int(x)]
-			off += int(x)
+			index.valuePos = o
+			index.valueLen = int(x)
+			o += index.valueLen
+		} else {
+			index.valuePos = 0
+			index.valueLen = 0
 		}
 
-		if err := f(i, kt, key, value); err != nil {
+		if err := fn(i, index); err != nil {
 			return err
 		}
 	}
-
 	return nil
 }
 
-func (b *Batch) memReplay(to *memdb.DB) error {
-	var ikScratch []byte
-	return b.decodeRec(func(i int, kt keyType, key, value []byte) error {
-		ikScratch = makeInternalKey(ikScratch, key, b.seq+uint64(i), kt)
-		return to.Put(ikScratch, value)
+func decodeBatchToMem(data []byte, expectSeq uint64, mdb *memdb.DB) (seq uint64, batchLen int, err error) {
+	seq, batchLen, err = decodeBatchHeader(data)
+	if err != nil {
+		return 0, 0, err
+	}
+	if seq < expectSeq {
+		return 0, 0, newErrBatchCorrupted("invalid sequence number")
+	}
+	data = data[batchHeaderLen:]
+	var ik []byte
+	var decodedLen int
+	err = decodeBatch(data, func(i int, index batchIndex) error {
+		if i >= batchLen {
+			return newErrBatchCorrupted("invalid records length")
+		}
+		ik = makeInternalKey(ik, index.k(data), seq+uint64(i), index.keyType)
+		if err := mdb.Put(ik, index.v(data)); err != nil {
+			return err
+		}
+		decodedLen++
+		return nil
 	})
+	if err == nil && decodedLen != batchLen {
+		err = newErrBatchCorrupted(fmt.Sprintf("invalid records length: %d vs %d", batchLen, decodedLen))
+	}
+	return
 }
 
-func (b *Batch) memDecodeAndReplay(prevSeq uint64, data []byte, to *memdb.DB) error {
-	if err := b.decode(prevSeq, data); err != nil {
-		return err
+func encodeBatchHeader(dst []byte, seq uint64, batchLen int) []byte {
+	dst = ensureBuffer(dst, batchHeaderLen)
+	binary.LittleEndian.PutUint64(dst, seq)
+	binary.LittleEndian.PutUint32(dst[8:], uint32(batchLen))
+	return dst
+}
+
+func decodeBatchHeader(data []byte) (seq uint64, batchLen int, err error) {
+	if len(data) < batchHeaderLen {
+		return 0, 0, newErrBatchCorrupted("too short")
+	}
+
+	seq = binary.LittleEndian.Uint64(data)
+	batchLen = int(binary.LittleEndian.Uint32(data[8:]))
+	if batchLen < 0 {
+		return 0, 0, newErrBatchCorrupted("invalid records length")
 	}
-	return b.memReplay(to)
+	return
 }
 
-func (b *Batch) revertMemReplay(to *memdb.DB) error {
-	var ikScratch []byte
-	return b.decodeRec(func(i int, kt keyType, key, value []byte) error {
-		ikScratch := makeInternalKey(ikScratch, key, b.seq+uint64(i), kt)
-		return to.Delete(ikScratch)
-	})
+func batchesLen(batches []*Batch) int {
+	batchLen := 0
+	for _, batch := range batches {
+		batchLen += batch.Len()
+	}
+	return batchLen
+}
+
+func writeBatchesWithHeader(wr io.Writer, batches []*Batch, seq uint64) error {
+	if _, err := wr.Write(encodeBatchHeader(nil, seq, batchesLen(batches))); err != nil {
+		return err
+	}
+	for _, batch := range batches {
+		if _, err := wr.Write(batch.data); err != nil {
+			return err
+		}
+	}
+	return nil
 }
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/cache/cache.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/cache/cache.go
index a287d0e5e..c5940b232 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/cache/cache.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/cache/cache.go
@@ -16,7 +16,7 @@ import (
 )
 
 // Cacher provides interface to implements a caching functionality.
-// An implementation must be goroutine-safe.
+// An implementation must be safe for concurrent use.
 type Cacher interface {
 	// Capacity returns cache capacity.
 	Capacity() int
@@ -511,18 +511,12 @@ func (r *Cache) EvictAll() {
 	}
 }
 
-// Close closes the 'cache map' and releases all 'cache node'.
+// Close closes the 'cache map' and forcefully releases all 'cache node'.
 func (r *Cache) Close() error {
 	r.mu.Lock()
 	if !r.closed {
 		r.closed = true
 
-		if r.cacher != nil {
-			if err := r.cacher.Close(); err != nil {
-				return err
-			}
-		}
-
 		h := (*mNode)(r.mHead)
 		h.initBuckets()
 
@@ -541,10 +535,37 @@ func (r *Cache) Close() error {
 				for _, f := range n.onDel {
 					f()
 				}
+				n.onDel = nil
 			}
 		}
 	}
 	r.mu.Unlock()
+
+	// Avoid deadlock.
+	if r.cacher != nil {
+		if err := r.cacher.Close(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// CloseWeak closes the 'cache map' and evict all 'cache node' from cacher, but
+// unlike Close it doesn't forcefully releases 'cache node'.
+func (r *Cache) CloseWeak() error {
+	r.mu.Lock()
+	if !r.closed {
+		r.closed = true
+	}
+	r.mu.Unlock()
+
+	// Avoid deadlock.
+	if r.cacher != nil {
+		r.cacher.EvictAll()
+		if err := r.cacher.Close(); err != nil {
+			return err
+		}
+	}
 	return nil
 }
 
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/comparer.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/comparer.go
index 248bf7c21..448402b82 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/comparer.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/comparer.go
@@ -6,7 +6,9 @@
 
 package leveldb
 
-import "github.com/syndtr/goleveldb/leveldb/comparer"
+import (
+	"github.com/syndtr/goleveldb/leveldb/comparer"
+)
 
 type iComparer struct {
 	ucmp comparer.Comparer
@@ -33,12 +35,12 @@ func (icmp *iComparer) Name() string {
 }
 
 func (icmp *iComparer) Compare(a, b []byte) int {
-	x := icmp.ucmp.Compare(internalKey(a).ukey(), internalKey(b).ukey())
+	x := icmp.uCompare(internalKey(a).ukey(), internalKey(b).ukey())
 	if x == 0 {
 		if m, n := internalKey(a).num(), internalKey(b).num(); m > n {
-			x = -1
+			return -1
 		} else if m < n {
-			x = 1
+			return 1
 		}
 	}
 	return x
@@ -46,30 +48,20 @@ func (icmp *iComparer) Compare(a, b []byte) int {
 
 func (icmp *iComparer) Separator(dst, a, b []byte) []byte {
 	ua, ub := internalKey(a).ukey(), internalKey(b).ukey()
-	dst = icmp.ucmp.Separator(dst, ua, ub)
-	if dst == nil {
-		return nil
+	dst = icmp.uSeparator(dst, ua, ub)
+	if dst != nil && len(dst) < len(ua) && icmp.uCompare(ua, dst) < 0 {
+		// Append earliest possible number.
+		return append(dst, keyMaxNumBytes...)
 	}
-	if len(dst) < len(ua) && icmp.uCompare(ua, dst) < 0 {
-		dst = append(dst, keyMaxNumBytes...)
-	} else {
-		// Did not close possibilities that n maybe longer than len(ub).
-		dst = append(dst, a[len(a)-8:]...)
-	}
-	return dst
+	return nil
 }
 
 func (icmp *iComparer) Successor(dst, b []byte) []byte {
 	ub := internalKey(b).ukey()
-	dst = icmp.ucmp.Successor(dst, ub)
-	if dst == nil {
-		return nil
-	}
-	if len(dst) < len(ub) && icmp.uCompare(ub, dst) < 0 {
-		dst = append(dst, keyMaxNumBytes...)
-	} else {
-		// Did not close possibilities that n maybe longer than len(ub).
-		dst = append(dst, b[len(b)-8:]...)
+	dst = icmp.uSuccessor(dst, ub)
+	if dst != nil && len(dst) < len(ub) && icmp.uCompare(ub, dst) < 0 {
+		// Append earliest possible number.
+		return append(dst, keyMaxNumBytes...)
 	}
-	return dst
+	return nil
 }
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db.go
index eb6abd0fb..a02cb2c50 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db.go
@@ -53,14 +53,13 @@ type DB struct {
 	aliveSnaps, aliveIters int32
 
 	// Write.
-	writeC       chan *Batch
+	batchPool    sync.Pool
+	writeMergeC  chan writeMerge
 	writeMergedC chan bool
 	writeLockC   chan struct{}
 	writeAckC    chan error
 	writeDelay   time.Duration
 	writeDelayN  int
-	journalC     chan *Batch
-	journalAckC  chan error
 	tr           *Transaction
 
 	// Compaction.
@@ -94,12 +93,11 @@ func openDB(s *session) (*DB, error) {
 		// Snapshot
 		snapsList: list.New(),
 		// Write
-		writeC:       make(chan *Batch),
+		batchPool:    sync.Pool{New: newBatch},
+		writeMergeC:  make(chan writeMerge),
 		writeMergedC: make(chan bool),
 		writeLockC:   make(chan struct{}, 1),
 		writeAckC:    make(chan error),
-		journalC:     make(chan *Batch),
-		journalAckC:  make(chan error),
 		// Compaction
 		tcompCmdC:   make(chan cCmd),
 		tcompPauseC: make(chan chan<- struct{}),
@@ -144,10 +142,10 @@ func openDB(s *session) (*DB, error) {
 	if readOnly {
 		db.SetReadOnly()
 	} else {
-		db.closeW.Add(3)
+		db.closeW.Add(2)
 		go db.tCompaction()
 		go db.mCompaction()
-		go db.jWriter()
+		// go db.jWriter()
 	}
 
 	s.logf("db@open done T·%v", time.Since(start))
@@ -162,10 +160,10 @@ func openDB(s *session) (*DB, error) {
 // os.ErrExist error.
 //
 // Open will return an error with type of ErrCorrupted if corruption
-// detected in the DB. Corrupted DB can be recovered with Recover
-// function.
+// detected in the DB. Use errors.IsCorrupted to test whether an error is
+// due to corruption. Corrupted DB can be recovered with Recover function.
 //
-// The returned DB instance is goroutine-safe.
+// The returned DB instance is safe for concurrent use.
 // The DB must be closed after use, by calling Close method.
 func Open(stor storage.Storage, o *opt.Options) (db *DB, err error) {
 	s, err := newSession(stor, o)
@@ -202,13 +200,13 @@ func Open(stor storage.Storage, o *opt.Options) (db *DB, err error) {
 // os.ErrExist error.
 //
 // OpenFile uses standard file-system backed storage implementation as
-// desribed in the leveldb/storage package.
+// described in the leveldb/storage package.
 //
 // OpenFile will return an error with type of ErrCorrupted if corruption
-// detected in the DB. Corrupted DB can be recovered with Recover
-// function.
+// detected in the DB. Use errors.IsCorrupted to test whether an error is
+// due to corruption. Corrupted DB can be recovered with Recover function.
 //
-// The returned DB instance is goroutine-safe.
+// The returned DB instance is safe for concurrent use.
 // The DB must be closed after use, by calling Close method.
 func OpenFile(path string, o *opt.Options) (db *DB, err error) {
 	stor, err := storage.OpenFile(path, o.GetReadOnly())
@@ -229,7 +227,7 @@ func OpenFile(path string, o *opt.Options) (db *DB, err error) {
 // The DB must already exist or it will returns an error.
 // Also, Recover will ignore ErrorIfMissing and ErrorIfExist options.
 //
-// The returned DB instance is goroutine-safe.
+// The returned DB instance is safe for concurrent use.
 // The DB must be closed after use, by calling Close method.
 func Recover(stor storage.Storage, o *opt.Options) (db *DB, err error) {
 	s, err := newSession(stor, o)
@@ -255,10 +253,10 @@ func Recover(stor storage.Storage, o *opt.Options) (db *DB, err error) {
 // The DB must already exist or it will returns an error.
 // Also, Recover will ignore ErrorIfMissing and ErrorIfExist options.
 //
-// RecoverFile uses standard file-system backed storage implementation as desribed
+// RecoverFile uses standard file-system backed storage implementation as described
 // in the leveldb/storage package.
 //
-// The returned DB instance is goroutine-safe.
+// The returned DB instance is safe for concurrent use.
 // The DB must be closed after use, by calling Close method.
 func RecoverFile(path string, o *opt.Options) (db *DB, err error) {
 	stor, err := storage.OpenFile(path, false)
@@ -504,10 +502,11 @@ func (db *DB) recoverJournal() error {
 			checksum    = db.s.o.GetStrict(opt.StrictJournalChecksum)
 			writeBuffer = db.s.o.GetWriteBuffer()
 
-			jr    *journal.Reader
-			mdb   = memdb.New(db.s.icmp, writeBuffer)
-			buf   = &util.Buffer{}
-			batch = &Batch{}
+			jr       *journal.Reader
+			mdb      = memdb.New(db.s.icmp, writeBuffer)
+			buf      = &util.Buffer{}
+			batchSeq uint64
+			batchLen int
 		)
 
 		for _, fd := range fds {
@@ -526,7 +525,7 @@ func (db *DB) recoverJournal() error {
 			}
 
 			// Flush memdb and remove obsolete journal file.
-			if !ofd.Nil() {
+			if !ofd.Zero() {
 				if mdb.Len() > 0 {
 					if _, err := db.s.flushMemdb(rec, mdb, 0); err != nil {
 						fr.Close()
@@ -569,7 +568,8 @@ func (db *DB) recoverJournal() error {
 					fr.Close()
 					return errors.SetFd(err, fd)
 				}
-				if err := batch.memDecodeAndReplay(db.seq, buf.Bytes(), mdb); err != nil {
+				batchSeq, batchLen, err = decodeBatchToMem(buf.Bytes(), db.seq, mdb)
+				if err != nil {
 					if !strict && errors.IsCorrupted(err) {
 						db.s.logf("journal error: %v (skipped)", err)
 						// We won't apply sequence number as it might be corrupted.
@@ -581,7 +581,7 @@ func (db *DB) recoverJournal() error {
 				}
 
 				// Save sequence number.
-				db.seq = batch.seq + uint64(batch.Len())
+				db.seq = batchSeq + uint64(batchLen)
 
 				// Flush it if large enough.
 				if mdb.Size() >= writeBuffer {
@@ -624,7 +624,7 @@ func (db *DB) recoverJournal() error {
 	}
 
 	// Remove the last obsolete journal file.
-	if !ofd.Nil() {
+	if !ofd.Zero() {
 		db.s.stor.Remove(ofd)
 	}
 
@@ -661,9 +661,10 @@ func (db *DB) recoverJournalRO() error {
 		db.logf("journal@recovery RO·Mode F·%d", len(fds))
 
 		var (
-			jr    *journal.Reader
-			buf   = &util.Buffer{}
-			batch = &Batch{}
+			jr       *journal.Reader
+			buf      = &util.Buffer{}
+			batchSeq uint64
+			batchLen int
 		)
 
 		for _, fd := range fds {
@@ -703,7 +704,8 @@ func (db *DB) recoverJournalRO() error {
 					fr.Close()
 					return errors.SetFd(err, fd)
 				}
-				if err := batch.memDecodeAndReplay(db.seq, buf.Bytes(), mdb); err != nil {
+				batchSeq, batchLen, err = decodeBatchToMem(buf.Bytes(), db.seq, mdb)
+				if err != nil {
 					if !strict && errors.IsCorrupted(err) {
 						db.s.logf("journal error: %v (skipped)", err)
 						// We won't apply sequence number as it might be corrupted.
@@ -715,7 +717,7 @@ func (db *DB) recoverJournalRO() error {
 				}
 
 				// Save sequence number.
-				db.seq = batch.seq + uint64(batch.Len())
+				db.seq = batchSeq + uint64(batchLen)
 			}
 
 			fr.Close()
@@ -856,7 +858,7 @@ func (db *DB) Has(key []byte, ro *opt.ReadOptions) (ret bool, err error) {
 
 // NewIterator returns an iterator for the latest snapshot of the
 // underlying DB.
-// The returned iterator is not goroutine-safe, but it is safe to use
+// 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 with modifying its
 // underlying DB. The resultant key/value pairs are guaranteed to be
@@ -1062,6 +1064,8 @@ func (db *DB) Close() error {
 	if db.journal != nil {
 		db.journal.Close()
 		db.journalWriter.Close()
+		db.journal = nil
+		db.journalWriter = nil
 	}
 
 	if db.writeDelayN > 0 {
@@ -1077,15 +1081,11 @@ func (db *DB) Close() error {
 		if err1 := db.closer.Close(); err == nil {
 			err = err1
 		}
+		db.closer = nil
 	}
 
-	// NIL'ing pointers.
-	db.s = nil
-	db.mem = nil
-	db.frozenMem = nil
-	db.journal = nil
-	db.journalWriter = nil
-	db.closer = nil
+	// Clear memdbs.
+	db.clearMems()
 
 	return err
 }
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_compaction.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_compaction.go
index 659f00dc6..2d0ad0753 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_compaction.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_compaction.go
@@ -96,7 +96,7 @@ noerr:
 			default:
 				goto haserr
 			}
-		case _, _ = <-db.closeC:
+		case <-db.closeC:
 			return
 		}
 	}
@@ -113,7 +113,7 @@ haserr:
 				goto hasperr
 			default:
 			}
-		case _, _ = <-db.closeC:
+		case <-db.closeC:
 			return
 		}
 	}
@@ -126,7 +126,7 @@ hasperr:
 		case db.writeLockC <- struct{}{}:
 			// Hold write lock, so that write won't pass-through.
 			db.compWriteLocking = true
-		case _, _ = <-db.closeC:
+		case <-db.closeC:
 			if db.compWriteLocking {
 				// We should release the lock or Close will hang.
 				<-db.writeLockC
@@ -195,7 +195,7 @@ func (db *DB) compactionTransact(name string, t compactionTransactInterface) {
 				db.logf("%s exiting (persistent error %q)", name, perr)
 				db.compactionExitTransact()
 			}
-		case _, _ = <-db.closeC:
+		case <-db.closeC:
 			db.logf("%s exiting", name)
 			db.compactionExitTransact()
 		}
@@ -224,7 +224,7 @@ func (db *DB) compactionTransact(name string, t compactionTransactInterface) {
 			}
 			select {
 			case <-backoffT.C:
-			case _, _ = <-db.closeC:
+			case <-db.closeC:
 				db.logf("%s exiting", name)
 				db.compactionExitTransact()
 			}
@@ -288,7 +288,7 @@ func (db *DB) memCompaction() {
 	case <-db.compPerErrC:
 		close(resumeC)
 		resumeC = nil
-	case _, _ = <-db.closeC:
+	case <-db.closeC:
 		return
 	}
 
@@ -337,7 +337,7 @@ func (db *DB) memCompaction() {
 		select {
 		case <-resumeC:
 			close(resumeC)
-		case _, _ = <-db.closeC:
+		case <-db.closeC:
 			return
 		}
 	}
@@ -378,7 +378,7 @@ func (b *tableCompactionBuilder) appendKV(key, value []byte) error {
 			select {
 			case ch := <-b.db.tcompPauseC:
 				b.db.pauseCompaction(ch)
-			case _, _ = <-b.db.closeC:
+			case <-b.db.closeC:
 				b.db.compactionExitTransact()
 			default:
 			}
@@ -643,7 +643,7 @@ func (db *DB) tableNeedCompaction() bool {
 func (db *DB) pauseCompaction(ch chan<- struct{}) {
 	select {
 	case ch <- struct{}{}:
-	case _, _ = <-db.closeC:
+	case <-db.closeC:
 		db.compactionExitTransact()
 	}
 }
@@ -697,14 +697,14 @@ func (db *DB) compTriggerWait(compC chan<- cCmd) (err error) {
 	case compC <- cAuto{ch}:
 	case err = <-db.compErrC:
 		return
-	case _, _ = <-db.closeC:
+	case <-db.closeC:
 		return ErrClosed
 	}
 	// Wait cmd.
 	select {
 	case err = <-ch:
 	case err = <-db.compErrC:
-	case _, _ = <-db.closeC:
+	case <-db.closeC:
 		return ErrClosed
 	}
 	return err
@@ -719,14 +719,14 @@ func (db *DB) compTriggerRange(compC chan<- cCmd, level int, min, max []byte) (e
 	case compC <- cRange{level, min, max, ch}:
 	case err := <-db.compErrC:
 		return err
-	case _, _ = <-db.closeC:
+	case <-db.closeC:
 		return ErrClosed
 	}
 	// Wait cmd.
 	select {
 	case err = <-ch:
 	case err = <-db.compErrC:
-	case _, _ = <-db.closeC:
+	case <-db.closeC:
 		return ErrClosed
 	}
 	return err
@@ -758,7 +758,7 @@ func (db *DB) mCompaction() {
 			default:
 				panic("leveldb: unknown command")
 			}
-		case _, _ = <-db.closeC:
+		case <-db.closeC:
 			return
 		}
 	}
@@ -791,7 +791,7 @@ func (db *DB) tCompaction() {
 			case ch := <-db.tcompPauseC:
 				db.pauseCompaction(ch)
 				continue
-			case _, _ = <-db.closeC:
+			case <-db.closeC:
 				return
 			default:
 			}
@@ -806,7 +806,7 @@ func (db *DB) tCompaction() {
 			case ch := <-db.tcompPauseC:
 				db.pauseCompaction(ch)
 				continue
-			case _, _ = <-db.closeC:
+			case <-db.closeC:
 				return
 			}
 		}
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_snapshot.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_snapshot.go
index 977f65ba5..2c69d2e53 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_snapshot.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_snapshot.go
@@ -59,7 +59,7 @@ func (db *DB) releaseSnapshot(se *snapshotElement) {
 	}
 }
 
-// Gets minimum sequence that not being snapshoted.
+// Gets minimum sequence that not being snapshotted.
 func (db *DB) minSeq() uint64 {
 	db.snapsMu.Lock()
 	defer db.snapsMu.Unlock()
@@ -131,7 +131,7 @@ func (snap *Snapshot) Has(key []byte, ro *opt.ReadOptions) (ret bool, err error)
 }
 
 // NewIterator returns an iterator for the snapshot of the underlying DB.
-// The returned iterator is not goroutine-safe, but it is safe to use
+// 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 with modifying its
 // underlying DB. The resultant key/value pairs are guaranteed to be
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_state.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_state.go
index 40f454da1..85b02d24b 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_state.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_state.go
@@ -67,12 +67,11 @@ func (db *DB) sampleSeek(ikey internalKey) {
 }
 
 func (db *DB) mpoolPut(mem *memdb.DB) {
-	defer func() {
-		recover()
-	}()
-	select {
-	case db.memPool <- mem:
-	default:
+	if !db.isClosed() {
+		select {
+		case db.memPool <- mem:
+		default:
+		}
 	}
 }
 
@@ -100,7 +99,13 @@ func (db *DB) mpoolDrain() {
 			case <-db.memPool:
 			default:
 			}
-		case _, _ = <-db.closeC:
+		case <-db.closeC:
+			ticker.Stop()
+			// Make sure the pool is drained.
+			select {
+			case <-db.memPool:
+			case <-time.After(time.Second):
+			}
 			close(db.memPool)
 			return
 		}
@@ -148,24 +153,26 @@ func (db *DB) newMem(n int) (mem *memDB, err error) {
 func (db *DB) getMems() (e, f *memDB) {
 	db.memMu.RLock()
 	defer db.memMu.RUnlock()
-	if db.mem == nil {
+	if db.mem != nil {
+		db.mem.incref()
+	} else if !db.isClosed() {
 		panic("nil effective mem")
 	}
-	db.mem.incref()
 	if db.frozenMem != nil {
 		db.frozenMem.incref()
 	}
 	return db.mem, db.frozenMem
 }
 
-// Get frozen memdb.
+// Get effective memdb.
 func (db *DB) getEffectiveMem() *memDB {
 	db.memMu.RLock()
 	defer db.memMu.RUnlock()
-	if db.mem == nil {
+	if db.mem != nil {
+		db.mem.incref()
+	} else if !db.isClosed() {
 		panic("nil effective mem")
 	}
-	db.mem.incref()
 	return db.mem
 }
 
@@ -200,6 +207,14 @@ func (db *DB) dropFrozenMem() {
 	db.memMu.Unlock()
 }
 
+// Clear mems ptr; used by DB.Close().
+func (db *DB) clearMems() {
+	db.memMu.Lock()
+	db.mem = nil
+	db.frozenMem = nil
+	db.memMu.Unlock()
+}
+
 // Set closed flag; return true if not already closed.
 func (db *DB) setClosed() bool {
 	return atomic.CompareAndSwapUint32(&db.closed, 0, 1)
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_transaction.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_transaction.go
index fca88037b..b8f7e7d21 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_transaction.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_transaction.go
@@ -59,8 +59,8 @@ func (tr *Transaction) Has(key []byte, ro *opt.ReadOptions) (bool, error) {
 }
 
 // NewIterator returns an iterator for the latest snapshot of the transaction.
-// The returned iterator is not goroutine-safe, but it is safe to use multiple
-// iterators concurrently, with each in a dedicated goroutine.
+// 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.
 //
@@ -167,8 +167,8 @@ func (tr *Transaction) Write(b *Batch, wo *opt.WriteOptions) error {
 	if tr.closed {
 		return errTransactionDone
 	}
-	return b.decodeRec(func(i int, kt keyType, key, value []byte) error {
-		return tr.put(kt, key, value)
+	return b.replayInternal(func(i int, kt keyType, k, v []byte) error {
+		return tr.put(kt, k, v)
 	})
 }
 
@@ -179,7 +179,8 @@ func (tr *Transaction) setDone() {
 	<-tr.db.writeLockC
 }
 
-// Commit commits the transaction.
+// 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 {
@@ -192,24 +193,27 @@ func (tr *Transaction) Commit() error {
 	if tr.closed {
 		return errTransactionDone
 	}
-	defer tr.setDone()
 	if err := tr.flush(); err != nil {
-		tr.discard()
+		// 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()
-		defer tr.db.compCommitLk.Unlock()
+		tr.stats.startTimer()
+		var cerr error
 		for retry := 0; retry < 3; retry++ {
-			if err := tr.db.s.commit(&tr.rec); err != nil {
-				tr.db.logf("transaction@commit error R·%d %q", retry, err)
+			cerr = tr.db.s.commit(&tr.rec)
+			if cerr != nil {
+				tr.db.logf("transaction@commit error R·%d %q", retry, cerr)
 				select {
 				case <-time.After(time.Second):
-				case _, _ = <-tr.db.closeC:
+				case <-tr.db.closeC:
 					tr.db.logf("transaction@commit exiting")
-					return err
+					tr.db.compCommitLk.Unlock()
+					return cerr
 				}
 			} else {
 				// Success. Set db.seq.
@@ -217,9 +221,26 @@ func (tr *Transaction) Commit() error {
 				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
 }
 
@@ -245,10 +266,20 @@ func (tr *Transaction) Discard() {
 	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. Write will be blocked until the transaction is committed or
-// discarded.
-// The returned transaction handle is goroutine-safe.
+// 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.
@@ -263,7 +294,7 @@ func (db *DB) OpenTransaction() (*Transaction, error) {
 	case db.writeLockC <- struct{}{}:
 	case err := <-db.compPerErrC:
 		return nil, err
-	case _, _ = <-db.closeC:
+	case <-db.closeC:
 		return nil, ErrClosed
 	}
 
@@ -278,6 +309,11 @@ func (db *DB) OpenTransaction() (*Transaction, error) {
 		}
 	}
 
+	// Wait compaction when certain threshold reached.
+	if err := db.waitCompaction(); err != nil {
+		return nil, err
+	}
+
 	tr := &Transaction{
 		db:  db,
 		seq: db.seq,
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_util.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_util.go
index 7fd386ca4..7ecd960d2 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_util.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_util.go
@@ -62,7 +62,7 @@ func (db *DB) checkAndCleanFiles() error {
 		case storage.TypeManifest:
 			keep = fd.Num >= db.s.manifestFd.Num
 		case storage.TypeJournal:
-			if !db.frozenJournalFd.Nil() {
+			if !db.frozenJournalFd.Zero() {
 				keep = fd.Num >= db.frozenJournalFd.Num
 			} else {
 				keep = fd.Num >= db.journalFd.Num
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_write.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_write.go
index 5576761fe..cc428b695 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_write.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_write.go
@@ -14,37 +14,23 @@ import (
 	"github.com/syndtr/goleveldb/leveldb/util"
 )
 
-func (db *DB) writeJournal(b *Batch) error {
-	w, err := db.journal.Next()
+func (db *DB) writeJournal(batches []*Batch, seq uint64, sync bool) error {
+	wr, err := db.journal.Next()
 	if err != nil {
 		return err
 	}
-	if _, err := w.Write(b.encode()); err != nil {
+	if err := writeBatchesWithHeader(wr, batches, seq); err != nil {
 		return err
 	}
 	if err := db.journal.Flush(); err != nil {
 		return err
 	}
-	if b.sync {
+	if sync {
 		return db.journalWriter.Sync()
 	}
 	return nil
 }
 
-func (db *DB) jWriter() {
-	defer db.closeW.Done()
-	for {
-		select {
-		case b := <-db.journalC:
-			if b != nil {
-				db.journalAckC <- db.writeJournal(b)
-			}
-		case _, _ = <-db.closeC:
-			return
-		}
-	}
-}
-
 func (db *DB) rotateMem(n int, wait bool) (mem *memDB, err error) {
 	// Wait for pending memdb compaction.
 	err = db.compTriggerWait(db.mcompCmdC)
@@ -69,24 +55,29 @@ func (db *DB) rotateMem(n int, wait bool) (mem *memDB, err error) {
 
 func (db *DB) flush(n int) (mdb *memDB, mdbFree int, err error) {
 	delayed := false
+	slowdownTrigger := db.s.o.GetWriteL0SlowdownTrigger()
+	pauseTrigger := db.s.o.GetWriteL0PauseTrigger()
 	flush := func() (retry bool) {
-		v := db.s.version()
-		defer v.release()
 		mdb = db.getEffectiveMem()
+		if mdb == nil {
+			err = ErrClosed
+			return false
+		}
 		defer func() {
 			if retry {
 				mdb.decref()
 				mdb = nil
 			}
 		}()
+		tLen := db.s.tLen(0)
 		mdbFree = mdb.Free()
 		switch {
-		case v.tLen(0) >= db.s.o.GetWriteL0SlowdownTrigger() && !delayed:
+		case tLen >= slowdownTrigger && !delayed:
 			delayed = true
 			time.Sleep(time.Millisecond)
 		case mdbFree >= n:
 			return false
-		case v.tLen(0) >= db.s.o.GetWriteL0PauseTrigger():
+		case tLen >= pauseTrigger:
 			delayed = true
 			err = db.compTriggerWait(db.tcompCmdC)
 			if err != nil {
@@ -123,159 +114,250 @@ func (db *DB) flush(n int) (mdb *memDB, mdbFree int, err error) {
 	return
 }
 
-// Write apply the given batch to the DB. The batch will be applied
-// sequentially.
-//
-// It is safe to modify the contents of the arguments after Write returns.
-func (db *DB) Write(b *Batch, wo *opt.WriteOptions) (err error) {
-	err = db.ok()
-	if err != nil || b == nil || b.Len() == 0 {
-		return
+type writeMerge struct {
+	sync       bool
+	batch      *Batch
+	keyType    keyType
+	key, value []byte
+}
+
+func (db *DB) unlockWrite(overflow bool, merged int, err error) {
+	for i := 0; i < merged; i++ {
+		db.writeAckC <- err
+	}
+	if overflow {
+		// Pass lock to the next write (that failed to merge).
+		db.writeMergedC <- false
+	} else {
+		// Release lock.
+		<-db.writeLockC
 	}
+}
 
-	b.init(wo.GetSync() && !db.s.o.GetNoSync())
+// ourBatch if defined should equal with batch.
+func (db *DB) writeLocked(batch, ourBatch *Batch, merge, sync bool) error {
+	// Try to flush memdb. This method would also trying to throttle writes
+	// if it is too fast and compaction cannot catch-up.
+	mdb, mdbFree, err := db.flush(batch.internalLen)
+	if err != nil {
+		db.unlockWrite(false, 0, err)
+		return err
+	}
+	defer mdb.decref()
 
-	if b.size() > db.s.o.GetWriteBuffer() && !db.s.o.GetDisableLargeBatchTransaction() {
-		// Writes using transaction.
-		tr, err1 := db.OpenTransaction()
-		if err1 != nil {
-			return err1
+	var (
+		overflow bool
+		merged   int
+		batches  = []*Batch{batch}
+	)
+
+	if merge {
+		// Merge limit.
+		var mergeLimit int
+		if batch.internalLen > 128<<10 {
+			mergeLimit = (1 << 20) - batch.internalLen
+		} else {
+			mergeLimit = 128 << 10
 		}
-		if err1 := tr.Write(b, wo); err1 != nil {
-			tr.Discard()
-			return err1
+		mergeCap := mdbFree - batch.internalLen
+		if mergeLimit > mergeCap {
+			mergeLimit = mergeCap
 		}
-		return tr.Commit()
-	}
 
-	// The write happen synchronously.
-	select {
-	case db.writeC <- b:
-		if <-db.writeMergedC {
-			return <-db.writeAckC
+	merge:
+		for mergeLimit > 0 {
+			select {
+			case incoming := <-db.writeMergeC:
+				if incoming.batch != nil {
+					// Merge batch.
+					if incoming.batch.internalLen > mergeLimit {
+						overflow = true
+						break merge
+					}
+					batches = append(batches, incoming.batch)
+					mergeLimit -= incoming.batch.internalLen
+				} else {
+					// Merge put.
+					internalLen := len(incoming.key) + len(incoming.value) + 8
+					if internalLen > mergeLimit {
+						overflow = true
+						break merge
+					}
+					if ourBatch == nil {
+						ourBatch = db.batchPool.Get().(*Batch)
+						ourBatch.Reset()
+						batches = append(batches, ourBatch)
+					}
+					// We can use same batch since concurrent write doesn't
+					// guarantee write order.
+					ourBatch.appendRec(incoming.keyType, incoming.key, incoming.value)
+					mergeLimit -= internalLen
+				}
+				sync = sync || incoming.sync
+				merged++
+				db.writeMergedC <- true
+
+			default:
+				break merge
+			}
 		}
-		// Continue, the write lock already acquired by previous writer
-		// and handed out to us.
-	case db.writeLockC <- struct{}{}:
-	case err = <-db.compPerErrC:
-		return
-	case _, _ = <-db.closeC:
-		return ErrClosed
 	}
 
-	merged := 0
-	danglingMerge := false
-	defer func() {
-		for i := 0; i < merged; i++ {
-			db.writeAckC <- err
-		}
-		if danglingMerge {
-			// Only one dangling merge at most, so this is safe.
-			db.writeMergedC <- false
-		} else {
-			<-db.writeLockC
+	// Seq number.
+	seq := db.seq + 1
+
+	// Write journal.
+	if err := db.writeJournal(batches, seq, sync); err != nil {
+		db.unlockWrite(overflow, merged, err)
+		return err
+	}
+
+	// Put batches.
+	for _, batch := range batches {
+		if err := batch.putMem(seq, mdb.DB); err != nil {
+			panic(err)
 		}
-	}()
+		seq += uint64(batch.Len())
+	}
 
-	mdb, mdbFree, err := db.flush(b.size())
-	if err != nil {
-		return
+	// Incr seq number.
+	db.addSeq(uint64(batchesLen(batches)))
+
+	// Rotate memdb if it's reach the threshold.
+	if batch.internalLen >= mdbFree {
+		db.rotateMem(0, false)
 	}
-	defer mdb.decref()
 
-	// Calculate maximum size of the batch.
-	m := 1 << 20
-	if x := b.size(); x <= 128<<10 {
-		m = x + (128 << 10)
+	db.unlockWrite(overflow, merged, nil)
+	return nil
+}
+
+// Write apply the given batch to the DB. The batch records will be applied
+// sequentially. Write might be used concurrently, when used concurrently and
+// batch is small enough, write will try to merge the batches. Set NoWriteMerge
+// option to true to disable write merge.
+//
+// It is safe to modify the contents of the arguments after Write returns but
+// not before. Write will not modify content of the batch.
+func (db *DB) Write(batch *Batch, wo *opt.WriteOptions) error {
+	if err := db.ok(); err != nil || batch == nil || batch.Len() == 0 {
+		return err
 	}
-	m = minInt(m, mdbFree)
 
-	// Merge with other batch.
-drain:
-	for b.size() < m && !b.sync {
-		select {
-		case nb := <-db.writeC:
-			if b.size()+nb.size() <= m {
-				b.append(nb)
-				db.writeMergedC <- true
-				merged++
-			} else {
-				danglingMerge = true
-				break drain
-			}
-		default:
-			break drain
+	// If the batch size is larger than write buffer, it may justified to write
+	// using transaction instead. Using transaction the batch will be written
+	// into tables directly, skipping the journaling.
+	if batch.internalLen > db.s.o.GetWriteBuffer() && !db.s.o.GetDisableLargeBatchTransaction() {
+		tr, err := db.OpenTransaction()
+		if err != nil {
+			return err
+		}
+		if err := tr.Write(batch, wo); err != nil {
+			tr.Discard()
+			return err
 		}
+		return tr.Commit()
 	}
 
-	// Set batch first seq number relative from last seq.
-	b.seq = db.seq + 1
+	merge := !wo.GetNoWriteMerge() && !db.s.o.GetNoWriteMerge()
+	sync := wo.GetSync() && !db.s.o.GetNoSync()
 
-	// Write journal concurrently if it is large enough.
-	if b.size() >= (128 << 10) {
-		// Push the write batch to the journal writer
+	// Acquire write lock.
+	if merge {
 		select {
-		case db.journalC <- b:
-			// Write into memdb
-			if berr := b.memReplay(mdb.DB); berr != nil {
-				panic(berr)
+		case db.writeMergeC <- writeMerge{sync: sync, batch: batch}:
+			if <-db.writeMergedC {
+				// Write is merged.
+				return <-db.writeAckC
 			}
-		case err = <-db.compPerErrC:
-			return
-		case _, _ = <-db.closeC:
-			err = ErrClosed
-			return
+			// Write is not merged, the write lock is handed to us. Continue.
+		case db.writeLockC <- struct{}{}:
+			// Write lock acquired.
+		case err := <-db.compPerErrC:
+			// Compaction error.
+			return err
+		case <-db.closeC:
+			// Closed
+			return ErrClosed
 		}
-		// Wait for journal writer
+	} else {
 		select {
-		case err = <-db.journalAckC:
-			if err != nil {
-				// Revert memdb if error detected
-				if berr := b.revertMemReplay(mdb.DB); berr != nil {
-					panic(berr)
-				}
-				return
+		case db.writeLockC <- struct{}{}:
+			// Write lock acquired.
+		case err := <-db.compPerErrC:
+			// Compaction error.
+			return err
+		case <-db.closeC:
+			// Closed
+			return ErrClosed
+		}
+	}
+
+	return db.writeLocked(batch, nil, merge, sync)
+}
+
+func (db *DB) putRec(kt keyType, key, value []byte, wo *opt.WriteOptions) error {
+	if err := db.ok(); err != nil {
+		return err
+	}
+
+	merge := !wo.GetNoWriteMerge() && !db.s.o.GetNoWriteMerge()
+	sync := wo.GetSync() && !db.s.o.GetNoSync()
+
+	// Acquire write lock.
+	if merge {
+		select {
+		case db.writeMergeC <- writeMerge{sync: sync, keyType: kt, key: key, value: value}:
+			if <-db.writeMergedC {
+				// Write is merged.
+				return <-db.writeAckC
 			}
-		case _, _ = <-db.closeC:
-			err = ErrClosed
-			return
+			// Write is not merged, the write lock is handed to us. Continue.
+		case db.writeLockC <- struct{}{}:
+			// Write lock acquired.
+		case err := <-db.compPerErrC:
+			// Compaction error.
+			return err
+		case <-db.closeC:
+			// Closed
+			return ErrClosed
 		}
 	} else {
-		err = db.writeJournal(b)
-		if err != nil {
-			return
-		}
-		if berr := b.memReplay(mdb.DB); berr != nil {
-			panic(berr)
+		select {
+		case db.writeLockC <- struct{}{}:
+			// Write lock acquired.
+		case err := <-db.compPerErrC:
+			// Compaction error.
+			return err
+		case <-db.closeC:
+			// Closed
+			return ErrClosed
 		}
 	}
 
-	// Set last seq number.
-	db.addSeq(uint64(b.Len()))
-
-	if b.size() >= mdbFree {
-		db.rotateMem(0, false)
-	}
-	return
+	batch := db.batchPool.Get().(*Batch)
+	batch.Reset()
+	batch.appendRec(kt, key, value)
+	return db.writeLocked(batch, batch, merge, sync)
 }
 
 // Put sets the value for the given key. It overwrites any previous value
-// for that key; a DB is not a multi-map.
+// for that key; a DB is not a multi-map. Write merge also applies for Put, see
+// Write.
 //
-// It is safe to modify the contents of the arguments after Put returns.
+// It is safe to modify the contents of the arguments after Put returns but not
+// before.
 func (db *DB) Put(key, value []byte, wo *opt.WriteOptions) error {
-	b := new(Batch)
-	b.Put(key, value)
-	return db.Write(b, wo)
+	return db.putRec(keyTypeVal, key, value, wo)
 }
 
-// Delete deletes the value for the given key.
+// Delete deletes the value for the given key. Delete will not returns error if
+// key doesn't exist. Write merge also applies for Delete, see Write.
 //
-// It is safe to modify the contents of the arguments after Delete returns.
+// It is safe to modify the contents of the arguments after Delete returns but
+// not before.
 func (db *DB) Delete(key []byte, wo *opt.WriteOptions) error {
-	b := new(Batch)
-	b.Delete(key)
-	return db.Write(b, wo)
+	return db.putRec(keyTypeDel, key, nil, wo)
 }
 
 func isMemOverlaps(icmp *iComparer, mem *memdb.DB, min, max []byte) bool {
@@ -304,12 +386,15 @@ func (db *DB) CompactRange(r util.Range) error {
 	case db.writeLockC <- struct{}{}:
 	case err := <-db.compPerErrC:
 		return err
-	case _, _ = <-db.closeC:
+	case <-db.closeC:
 		return ErrClosed
 	}
 
 	// Check for overlaps in memdb.
 	mdb := db.getEffectiveMem()
+	if mdb == nil {
+		return ErrClosed
+	}
 	defer mdb.decref()
 	if isMemOverlaps(db.s.icmp, mdb.DB, r.Start, r.Limit) {
 		// Memdb compaction.
@@ -341,7 +426,7 @@ func (db *DB) SetReadOnly() error {
 		db.compWriteLocking = true
 	case err := <-db.compPerErrC:
 		return err
-	case _, _ = <-db.closeC:
+	case <-db.closeC:
 		return ErrClosed
 	}
 
@@ -350,7 +435,7 @@ func (db *DB) SetReadOnly() error {
 	case db.compErrSetC <- ErrReadOnly:
 	case perr := <-db.compPerErrC:
 		return perr
-	case _, _ = <-db.closeC:
+	case <-db.closeC:
 		return ErrClosed
 	}
 
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/errors.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/errors.go
index c8bd66a5a..de2649812 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/errors.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/errors.go
@@ -10,6 +10,7 @@ import (
 	"github.com/syndtr/goleveldb/leveldb/errors"
 )
 
+// Common errors.
 var (
 	ErrNotFound         = errors.ErrNotFound
 	ErrReadOnly         = errors.New("leveldb: read-only mode")
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/errors/errors.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/errors/errors.go
index 9a0f6e2c1..8d6146b6f 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/errors/errors.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/errors/errors.go
@@ -15,6 +15,7 @@ import (
 	"github.com/syndtr/goleveldb/leveldb/util"
 )
 
+// Common errors.
 var (
 	ErrNotFound    = New("leveldb: not found")
 	ErrReleased    = util.ErrReleased
@@ -34,11 +35,10 @@ type ErrCorrupted struct {
 }
 
 func (e *ErrCorrupted) Error() string {
-	if !e.Fd.Nil() {
+	if !e.Fd.Zero() {
 		return fmt.Sprintf("%v [file=%v]", e.Err, e.Fd)
-	} else {
-		return e.Err.Error()
 	}
+	return e.Err.Error()
 }
 
 // NewErrCorrupted creates new ErrCorrupted error.
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/iterator/iter.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/iterator/iter.go
index c2522860b..3b5553274 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/iterator/iter.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/iterator/iter.go
@@ -21,13 +21,13 @@ var (
 // IteratorSeeker is the interface that wraps the 'seeks method'.
 type IteratorSeeker interface {
 	// First moves the iterator to the first key/value pair. If the iterator
-	// only contains one key/value pair then First and Last whould moves
+	// only contains one key/value pair then First and Last would moves
 	// to the same key/value pair.
 	// It returns whether such pair exist.
 	First() bool
 
 	// Last moves the iterator to the last key/value pair. If the iterator
-	// only contains one key/value pair then First and Last whould moves
+	// only contains one key/value pair then First and Last would moves
 	// to the same key/value pair.
 	// It returns whether such pair exist.
 	Last() bool
@@ -48,7 +48,7 @@ type IteratorSeeker interface {
 	Prev() bool
 }
 
-// CommonIterator is the interface that wraps common interator methods.
+// CommonIterator is the interface that wraps common iterator methods.
 type CommonIterator interface {
 	IteratorSeeker
 
@@ -71,14 +71,15 @@ type CommonIterator interface {
 
 // Iterator iterates over a DB's key/value pairs in key order.
 //
-// When encouter an error any 'seeks method' will return false and will
+// When encounter an error any 'seeks method' will return false and will
 // yield no key/value pairs. The error can be queried by calling the Error
 // method. Calling Release is still necessary.
 //
 // An iterator must be released after use, but it is not necessary to read
 // an iterator until exhaustion.
-// Also, an iterator is not necessarily goroutine-safe, but it is safe to use
-// multiple iterators concurrently, with each in a dedicated goroutine.
+// Also, an iterator is not necessarily safe for concurrent use, but it is
+// safe to use multiple iterators concurrently, with each in a dedicated
+// goroutine.
 type Iterator interface {
 	CommonIterator
 
@@ -98,7 +99,7 @@ type Iterator interface {
 //
 // ErrorCallbackSetter implemented by indexed and merged iterator.
 type ErrorCallbackSetter interface {
-	// SetErrorCallback allows set an error callback of the coresponding
+	// SetErrorCallback allows set an error callback of the corresponding
 	// iterator. Use nil to clear the callback.
 	SetErrorCallback(f func(err error))
 }
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go
index 891098bb7..d094c3d0f 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go
@@ -180,34 +180,37 @@ func (r *Reader) nextChunk(first bool) error {
 			checksum := binary.LittleEndian.Uint32(r.buf[r.j+0 : r.j+4])
 			length := binary.LittleEndian.Uint16(r.buf[r.j+4 : r.j+6])
 			chunkType := r.buf[r.j+6]
-
+			unprocBlock := r.n - r.j
 			if checksum == 0 && length == 0 && chunkType == 0 {
 				// Drop entire block.
-				m := r.n - r.j
 				r.i = r.n
 				r.j = r.n
-				return r.corrupt(m, "zero header", false)
-			} else {
-				m := r.n - r.j
-				r.i = r.j + headerSize
-				r.j = r.j + headerSize + int(length)
-				if r.j > r.n {
-					// Drop entire block.
-					r.i = r.n
-					r.j = r.n
-					return r.corrupt(m, "chunk length overflows block", false)
-				} else if r.checksum && checksum != util.NewCRC(r.buf[r.i-1:r.j]).Value() {
-					// Drop entire block.
-					r.i = r.n
-					r.j = r.n
-					return r.corrupt(m, "checksum mismatch", false)
-				}
+				return r.corrupt(unprocBlock, "zero header", false)
+			}
+			if chunkType < fullChunkType || chunkType > lastChunkType {
+				// Drop entire block.
+				r.i = r.n
+				r.j = r.n
+				return r.corrupt(unprocBlock, fmt.Sprintf("invalid chunk type %#x", chunkType), false)
+			}
+			r.i = r.j + headerSize
+			r.j = r.j + headerSize + int(length)
+			if r.j > r.n {
+				// Drop entire block.
+				r.i = r.n
+				r.j = r.n
+				return r.corrupt(unprocBlock, "chunk length overflows block", false)
+			} else if r.checksum && checksum != util.NewCRC(r.buf[r.i-1:r.j]).Value() {
+				// Drop entire block.
+				r.i = r.n
+				r.j = r.n
+				return r.corrupt(unprocBlock, "checksum mismatch", false)
 			}
 			if first && chunkType != fullChunkType && chunkType != firstChunkType {
-				m := r.j - r.i
+				chunkLength := (r.j - r.i) + headerSize
 				r.i = r.j
 				// Report the error, but skip it.
-				return r.corrupt(m+headerSize, "orphan chunk", true)
+				return r.corrupt(chunkLength, "orphan chunk", true)
 			}
 			r.last = chunkType == fullChunkType || chunkType == lastChunkType
 			return nil
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/key.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/key.go
index d0b80aaf9..ad8f51ec8 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/key.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/key.go
@@ -37,14 +37,14 @@ func (kt keyType) String() string {
 	case keyTypeVal:
 		return "v"
 	}
-	return "x"
+	return fmt.Sprintf("<invalid:%#x>", uint(kt))
 }
 
 // Value types encoded as the last component of internal keys.
 // Don't modify; this value are saved to disk.
 const (
-	keyTypeDel keyType = iota
-	keyTypeVal
+	keyTypeDel = keyType(0)
+	keyTypeVal = keyType(1)
 )
 
 // keyTypeSeek defines the keyType that should be passed when constructing an
@@ -79,11 +79,7 @@ func makeInternalKey(dst, ukey []byte, seq uint64, kt keyType) internalKey {
 		panic("leveldb: invalid type")
 	}
 
-	if n := len(ukey) + 8; cap(dst) < n {
-		dst = make([]byte, n)
-	} else {
-		dst = dst[:n]
-	}
+	dst = ensureBuffer(dst, len(ukey)+8)
 	copy(dst, ukey)
 	binary.LittleEndian.PutUint64(dst[len(ukey):], (seq<<8)|uint64(kt))
 	return internalKey(dst)
@@ -143,5 +139,5 @@ func (ik internalKey) String() string {
 	if ukey, seq, kt, err := parseInternalKey(ik); err == nil {
 		return fmt.Sprintf("%s,%s%d", shorten(string(ukey)), kt, seq)
 	}
-	return "<invalid>"
+	return fmt.Sprintf("<invalid:%#x>", []byte(ik))
 }
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/memdb/memdb.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/memdb/memdb.go
index 1395bd928..18a19ed42 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/memdb/memdb.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/memdb/memdb.go
@@ -17,6 +17,7 @@ import (
 	"github.com/syndtr/goleveldb/leveldb/util"
 )
 
+// Common errors.
 var (
 	ErrNotFound     = errors.ErrNotFound
 	ErrIterReleased = errors.New("leveldb/memdb: iterator released")
@@ -385,7 +386,7 @@ func (p *DB) Find(key []byte) (rkey, value []byte, err error) {
 }
 
 // NewIterator returns an iterator of the DB.
-// The returned iterator is not goroutine-safe, but it is safe to use
+// 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 with modifying its
 // underlying DB. However, the resultant key/value pairs are not guaranteed
@@ -411,7 +412,7 @@ func (p *DB) Capacity() int {
 }
 
 // Size returns sum of keys and values length. Note that deleted
-// key/value will not be accouted for, but it will still consume
+// key/value will not be accounted for, but it will still consume
 // the buffer, since the buffer is append only.
 func (p *DB) Size() int {
 	p.mu.RLock()
@@ -453,11 +454,14 @@ func (p *DB) Reset() {
 	p.mu.Unlock()
 }
 
-// New creates a new initalized in-memory key/value DB. The capacity
+// New creates a new initialized in-memory key/value DB. The capacity
 // is the initial key/value buffer capacity. The capacity is advisory,
 // not enforced.
 //
-// The returned DB instance is goroutine-safe.
+// This DB is append-only, deleting an entry would remove entry node but not
+// reclaim KV buffer.
+//
+// The returned DB instance is safe for concurrent use.
 func New(cmp comparer.BasicComparer, capacity int) *DB {
 	p := &DB{
 		cmp:       cmp,
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/opt/options.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/opt/options.go
index 3d2bf1c02..44e7d9adc 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/opt/options.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/opt/options.go
@@ -312,6 +312,11 @@ type Options struct {
 	// The default is false.
 	NoSync bool
 
+	// NoWriteMerge allows disabling write merge.
+	//
+	// The default is false.
+	NoWriteMerge bool
+
 	// OpenFilesCacher provides cache algorithm for open files caching.
 	// Specify NoCacher to disable caching algorithm.
 	//
@@ -543,6 +548,13 @@ func (o *Options) GetNoSync() bool {
 	return o.NoSync
 }
 
+func (o *Options) GetNoWriteMerge() bool {
+	if o == nil {
+		return false
+	}
+	return o.NoWriteMerge
+}
+
 func (o *Options) GetOpenFilesCacher() Cacher {
 	if o == nil || o.OpenFilesCacher == nil {
 		return DefaultOpenFilesCacher
@@ -629,6 +641,11 @@ func (ro *ReadOptions) GetStrict(strict Strict) bool {
 // WriteOptions holds the optional parameters for 'write operation'. The
 // 'write operation' includes Write, Put and Delete.
 type WriteOptions struct {
+	// NoWriteMerge allows disabling write merge.
+	//
+	// The default is false.
+	NoWriteMerge bool
+
 	// Sync is whether to sync underlying writes from the OS buffer cache
 	// through to actual disk, if applicable. Setting Sync can result in
 	// slower writes.
@@ -644,6 +661,13 @@ type WriteOptions struct {
 	Sync bool
 }
 
+func (wo *WriteOptions) GetNoWriteMerge() bool {
+	if wo == nil {
+		return false
+	}
+	return wo.NoWriteMerge
+}
+
 func (wo *WriteOptions) GetSync() bool {
 	if wo == nil {
 		return false
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/session.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/session.go
index b0d3fef1d..f3e747701 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/session.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/session.go
@@ -18,7 +18,8 @@ import (
 	"github.com/syndtr/goleveldb/leveldb/storage"
 )
 
-// ErrManifestCorrupted records manifest corruption.
+// ErrManifestCorrupted records manifest corruption. This error will be
+// wrapped with errors.ErrCorrupted.
 type ErrManifestCorrupted struct {
 	Field  string
 	Reason string
@@ -42,7 +43,7 @@ type session struct {
 	stSeqNum         uint64 // last mem compacted seq; need external synchronization
 
 	stor     storage.Storage
-	storLock storage.Lock
+	storLock storage.Locker
 	o        *cachedOptions
 	icmp     *iComparer
 	tops     *tOps
@@ -87,12 +88,12 @@ func (s *session) close() {
 	}
 	s.manifest = nil
 	s.manifestWriter = nil
-	s.stVersion = nil
+	s.setVersion(&version{s: s, closing: true})
 }
 
 // Release session lock.
 func (s *session) release() {
-	s.storLock.Release()
+	s.storLock.Unlock()
 }
 
 // Create a new database session; need external synchronization.
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/session_util.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/session_util.go
index 674182fb2..34ad61798 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/session_util.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/session_util.go
@@ -50,6 +50,12 @@ func (s *session) version() *version {
 	return s.stVersion
 }
 
+func (s *session) tLen(level int) int {
+	s.vmu.Lock()
+	defer s.vmu.Unlock()
+	return s.stVersion.tLen(level)
+}
+
 // Set current version to v.
 func (s *session) setVersion(v *version) {
 	s.vmu.Lock()
@@ -197,7 +203,7 @@ func (s *session) newManifest(rec *sessionRecord, v *version) (err error) {
 			if s.manifestWriter != nil {
 				s.manifestWriter.Close()
 			}
-			if !s.manifestFd.Nil() {
+			if !s.manifestFd.Zero() {
 				s.stor.Remove(s.manifestFd)
 			}
 			s.manifestFd = fd
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/storage/file_storage.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/storage/file_storage.go
index cbe1dc103..e53434cab 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/storage/file_storage.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/storage/file_storage.go
@@ -32,7 +32,7 @@ type fileStorageLock struct {
 	fs *fileStorage
 }
 
-func (lock *fileStorageLock) Release() {
+func (lock *fileStorageLock) Unlock() {
 	if lock.fs != nil {
 		lock.fs.mu.Lock()
 		defer lock.fs.mu.Unlock()
@@ -116,7 +116,7 @@ func OpenFile(path string, readOnly bool) (Storage, error) {
 	return fs, nil
 }
 
-func (fs *fileStorage) Lock() (Lock, error) {
+func (fs *fileStorage) Lock() (Locker, error) {
 	fs.mu.Lock()
 	defer fs.mu.Unlock()
 	if fs.open < 0 {
@@ -323,7 +323,7 @@ func (fs *fileStorage) GetMeta() (fd FileDesc, err error) {
 		}
 	}
 	// Don't remove any files if there is no valid CURRENT file.
-	if fd.Nil() {
+	if fd.Zero() {
 		if cerr != nil {
 			err = cerr
 		} else {
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/storage/mem_storage.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/storage/mem_storage.go
index 9b70e1513..9b0421f03 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/storage/mem_storage.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/storage/mem_storage.go
@@ -18,7 +18,7 @@ type memStorageLock struct {
 	ms *memStorage
 }
 
-func (lock *memStorageLock) Release() {
+func (lock *memStorageLock) Unlock() {
 	ms := lock.ms
 	ms.mu.Lock()
 	defer ms.mu.Unlock()
@@ -43,7 +43,7 @@ func NewMemStorage() Storage {
 	}
 }
 
-func (ms *memStorage) Lock() (Lock, error) {
+func (ms *memStorage) Lock() (Locker, error) {
 	ms.mu.Lock()
 	defer ms.mu.Unlock()
 	if ms.slock != nil {
@@ -69,7 +69,7 @@ func (ms *memStorage) SetMeta(fd FileDesc) error {
 func (ms *memStorage) GetMeta() (FileDesc, error) {
 	ms.mu.Lock()
 	defer ms.mu.Unlock()
-	if ms.meta.Nil() {
+	if ms.meta.Zero() {
 		return FileDesc{}, os.ErrNotExist
 	}
 	return ms.meta, nil
@@ -78,7 +78,7 @@ func (ms *memStorage) GetMeta() (FileDesc, error) {
 func (ms *memStorage) List(ft FileType) ([]FileDesc, error) {
 	ms.mu.Lock()
 	var fds []FileDesc
-	for x, _ := range ms.files {
+	for x := range ms.files {
 		fd := unpackFile(x)
 		if fd.Type&ft != 0 {
 			fds = append(fds, fd)
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/storage/storage.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/storage/storage.go
index 9b30b6727..c16bce6b6 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/storage/storage.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/storage/storage.go
@@ -11,12 +11,12 @@ import (
 	"errors"
 	"fmt"
 	"io"
-
-	"github.com/syndtr/goleveldb/leveldb/util"
 )
 
+// FileType represent a file type.
 type FileType int
 
+// File types.
 const (
 	TypeManifest FileType = 1 << iota
 	TypeJournal
@@ -40,6 +40,7 @@ func (t FileType) String() string {
 	return fmt.Sprintf("<unknown:%d>", t)
 }
 
+// Common error.
 var (
 	ErrInvalidFile = errors.New("leveldb/storage: invalid file for argument")
 	ErrLocked      = errors.New("leveldb/storage: already locked")
@@ -55,11 +56,10 @@ type ErrCorrupted struct {
 }
 
 func (e *ErrCorrupted) Error() string {
-	if !e.Fd.Nil() {
+	if !e.Fd.Zero() {
 		return fmt.Sprintf("%v [file=%v]", e.Err, e.Fd)
-	} else {
-		return e.Err.Error()
 	}
+	return e.Err.Error()
 }
 
 // Syncer is the interface that wraps basic Sync method.
@@ -83,11 +83,12 @@ type Writer interface {
 	Syncer
 }
 
-type Lock interface {
-	util.Releaser
+// Locker is the interface that wraps Unlock method.
+type Locker interface {
+	Unlock()
 }
 
-// FileDesc is a file descriptor.
+// FileDesc is a 'file descriptor'.
 type FileDesc struct {
 	Type FileType
 	Num  int64
@@ -108,12 +109,12 @@ func (fd FileDesc) String() string {
 	}
 }
 
-// Nil returns true if fd == (FileDesc{}).
-func (fd FileDesc) Nil() bool {
+// Zero returns true if fd == (FileDesc{}).
+func (fd FileDesc) Zero() bool {
 	return fd == (FileDesc{})
 }
 
-// FileDescOk returns true if fd is a valid file descriptor.
+// FileDescOk returns true if fd is a valid 'file descriptor'.
 func FileDescOk(fd FileDesc) bool {
 	switch fd.Type {
 	case TypeManifest:
@@ -126,43 +127,44 @@ func FileDescOk(fd FileDesc) bool {
 	return fd.Num >= 0
 }
 
-// Storage is the storage. A storage instance must be goroutine-safe.
+// Storage is the storage. A storage instance must be safe for concurrent use.
 type Storage interface {
 	// Lock locks the storage. Any subsequent attempt to call Lock will fail
 	// until the last lock released.
-	// After use the caller should call the Release method.
-	Lock() (Lock, error)
+	// Caller should call Unlock method after use.
+	Lock() (Locker, error)
 
 	// Log logs a string. This is used for logging.
 	// An implementation may write to a file, stdout or simply do nothing.
 	Log(str string)
 
-	// SetMeta sets to point to the given fd, which then can be acquired using
-	// GetMeta method.
-	// SetMeta should be implemented in such way that changes should happened
+	// SetMeta store 'file descriptor' that can later be acquired using GetMeta
+	// method. The 'file descriptor' should point to a valid file.
+	// SetMeta should be implemented in such way that changes should happen
 	// atomically.
 	SetMeta(fd FileDesc) error
 
-	// GetManifest returns a manifest file.
-	// Returns os.ErrNotExist if meta doesn't point to any fd, or point to fd
-	// that doesn't exist.
+	// GetMeta returns 'file descriptor' stored in meta. The 'file descriptor'
+	// can be updated using SetMeta method.
+	// Returns os.ErrNotExist if meta doesn't store any 'file descriptor', or
+	// 'file descriptor' point to nonexistent file.
 	GetMeta() (FileDesc, error)
 
-	// List returns fds that match the given file types.
+	// List returns file descriptors that match the given file types.
 	// The file types may be OR'ed together.
 	List(ft FileType) ([]FileDesc, error)
 
-	// Open opens file with the given fd read-only.
+	// Open opens file with the given 'file descriptor' read-only.
 	// Returns os.ErrNotExist error if the file does not exist.
 	// Returns ErrClosed if the underlying storage is closed.
 	Open(fd FileDesc) (Reader, error)
 
-	// Create creates file with the given fd, truncate if already exist and
-	// opens write-only.
+	// Create creates file with the given 'file descriptor', truncate if already
+	// exist and opens write-only.
 	// Returns ErrClosed if the underlying storage is closed.
 	Create(fd FileDesc) (Writer, error)
 
-	// Remove removes file with the given fd.
+	// Remove removes file with the given 'file descriptor'.
 	// Returns ErrClosed if the underlying storage is closed.
 	Remove(fd FileDesc) error
 
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table.go
index 310ba6c22..81d18a531 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table.go
@@ -434,7 +434,7 @@ func (t *tOps) close() {
 	t.bpool.Close()
 	t.cache.Close()
 	if t.bcache != nil {
-		t.bcache.Close()
+		t.bcache.CloseWeak()
 	}
 }
 
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table/reader.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table/reader.go
index ae61bece9..c5be420b3 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table/reader.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table/reader.go
@@ -26,12 +26,15 @@ import (
 	"github.com/syndtr/goleveldb/leveldb/util"
 )
 
+// Reader errors.
 var (
 	ErrNotFound       = errors.ErrNotFound
 	ErrReaderReleased = errors.New("leveldb/table: reader released")
 	ErrIterReleased   = errors.New("leveldb/table: iterator released")
 )
 
+// ErrCorrupted describes error due to corruption. This error will be wrapped
+// with errors.ErrCorrupted.
 type ErrCorrupted struct {
 	Pos    int64
 	Size   int64
@@ -61,7 +64,7 @@ type block struct {
 func (b *block) seek(cmp comparer.Comparer, rstart, rlimit int, key []byte) (index, offset int, err error) {
 	index = sort.Search(b.restartsLen-rstart-(b.restartsLen-rlimit), func(i int) bool {
 		offset := int(binary.LittleEndian.Uint32(b.data[b.restartsOffset+4*(rstart+i):]))
-		offset += 1                                 // shared always zero, since this is a restart point
+		offset++                                    // shared always zero, since this is a restart point
 		v1, n1 := binary.Uvarint(b.data[offset:])   // key length
 		_, n2 := binary.Uvarint(b.data[offset+n1:]) // value length
 		m := offset + n1 + n2
@@ -356,7 +359,7 @@ func (i *blockIter) Prev() bool {
 	i.value = nil
 	offset := i.block.restartOffset(ri)
 	if offset == i.offset {
-		ri -= 1
+		ri--
 		if ri < 0 {
 			i.dir = dirSOI
 			return false
@@ -783,8 +786,8 @@ func (r *Reader) getDataIterErr(dataBH blockHandle, slice *util.Range, verifyChe
 // table. And a nil Range.Limit is treated as a key after all keys in
 // the table.
 //
-// The returned iterator is not goroutine-safe and should be released
-// when not used.
+// The returned iterator is not safe for concurrent use and should be released
+// after use.
 //
 // Also read Iterator documentation of the leveldb/iterator package.
 func (r *Reader) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator {
@@ -826,18 +829,21 @@ func (r *Reader) find(key []byte, filtered bool, ro *opt.ReadOptions, noValue bo
 
 	index := r.newBlockIter(indexBlock, nil, nil, true)
 	defer index.Release()
+
 	if !index.Seek(key) {
-		err = index.Error()
-		if err == nil {
+		if err = index.Error(); err == nil {
 			err = ErrNotFound
 		}
 		return
 	}
+
 	dataBH, n := decodeBlockHandle(index.Value())
 	if n == 0 {
 		r.err = r.newErrCorruptedBH(r.indexBH, "bad data block handle")
-		return
+		return nil, nil, r.err
 	}
+
+	// The filter should only used for exact match.
 	if filtered && r.filter != nil {
 		filterBlock, frel, ferr := r.getFilterBlock(true)
 		if ferr == nil {
@@ -847,30 +853,53 @@ func (r *Reader) find(key []byte, filtered bool, ro *opt.ReadOptions, noValue bo
 			}
 			frel.Release()
 		} else if !errors.IsCorrupted(ferr) {
-			err = ferr
-			return
+			return nil, nil, ferr
 		}
 	}
+
 	data := r.getDataIter(dataBH, nil, r.verifyChecksum, !ro.GetDontFillCache())
-	defer data.Release()
 	if !data.Seek(key) {
-		err = data.Error()
-		if err == nil {
-			err = ErrNotFound
+		data.Release()
+		if err = data.Error(); err != nil {
+			return
+		}
+
+		// The nearest greater-than key is the first key of the next block.
+		if !index.Next() {
+			if err = index.Error(); err == nil {
+				err = ErrNotFound
+			}
+			return
+		}
+
+		dataBH, n = decodeBlockHandle(index.Value())
+		if n == 0 {
+			r.err = r.newErrCorruptedBH(r.indexBH, "bad data block handle")
+			return nil, nil, r.err
+		}
+
+		data = r.getDataIter(dataBH, nil, r.verifyChecksum, !ro.GetDontFillCache())
+		if !data.Next() {
+			data.Release()
+			if err = data.Error(); err == nil {
+				err = ErrNotFound
+			}
+			return
 		}
-		return
 	}
-	// Don't use block buffer, no need to copy the buffer.
+
+	// Key doesn't use block buffer, no need to copy the buffer.
 	rkey = data.Key()
 	if !noValue {
 		if r.bpool == nil {
 			value = data.Value()
 		} else {
-			// Use block buffer, and since the buffer will be recycled, the buffer
-			// need to be copied.
+			// Value does use block buffer, and since the buffer will be
+			// recycled, it need to be copied.
 			value = append([]byte{}, data.Value()...)
 		}
 	}
+	data.Release()
 	return
 }
 
@@ -888,7 +917,7 @@ func (r *Reader) Find(key []byte, filtered bool, ro *opt.ReadOptions) (rkey, val
 	return r.find(key, filtered, ro, false)
 }
 
-// Find finds key that is greater than or equal to the given key.
+// FindKey finds key that is greater than or equal to the given key.
 // It returns ErrNotFound if the table doesn't contain such key.
 // If filtered is true then the nearest 'block' will be checked against
 // 'filter data' (if present) and will immediately return ErrNotFound if
@@ -987,7 +1016,7 @@ func (r *Reader) Release() {
 // NewReader creates a new initialized table reader for the file.
 // The fi, cache and bpool is optional and can be nil.
 //
-// The returned table reader instance is goroutine-safe.
+// The returned table reader instance is safe for concurrent use.
 func NewReader(f io.ReaderAt, size int64, fd storage.FileDesc, cache *cache.NamespaceGetter, bpool *util.BufferPool, o *opt.Options) (*Reader, error) {
 	if f == nil {
 		return nil, errors.New("leveldb/table: nil file")
@@ -1039,9 +1068,8 @@ func NewReader(f io.ReaderAt, size int64, fd storage.FileDesc, cache *cache.Name
 		if errors.IsCorrupted(err) {
 			r.err = err
 			return r, nil
-		} else {
-			return nil, err
 		}
+		return nil, err
 	}
 
 	// Set data end.
@@ -1086,9 +1114,8 @@ func NewReader(f io.ReaderAt, size int64, fd storage.FileDesc, cache *cache.Name
 			if errors.IsCorrupted(err) {
 				r.err = err
 				return r, nil
-			} else {
-				return nil, err
 			}
+			return nil, err
 		}
 		if r.filter != nil {
 			r.filterBlock, err = r.readFilterBlock(r.filterBH)
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table/writer.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table/writer.go
index 274dee6da..b96b271d8 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table/writer.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table/writer.go
@@ -349,7 +349,7 @@ func (w *Writer) Close() error {
 
 // NewWriter creates a new initialized table writer for the file.
 //
-// Table writer is not goroutine-safe.
+// Table writer is not safe for concurrent use.
 func NewWriter(f io.Writer, o *opt.Options) *Writer {
 	w := &Writer{
 		writer:          f,
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/util.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/util.go
index 3b663d1cc..e572a329e 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/util.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/util.go
@@ -89,3 +89,10 @@ func (p fdSorter) Swap(i, j int) {
 func sortFds(fds []storage.FileDesc) {
 	sort.Sort(fdSorter(fds))
 }
+
+func ensureBuffer(b []byte, n int) []byte {
+	if cap(b) < n {
+		return make([]byte, n)
+	}
+	return b[:n]
+}
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/version.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/version.go
index d274eeff2..c60f12c20 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/version.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/version.go
@@ -34,7 +34,8 @@ type version struct {
 
 	cSeek unsafe.Pointer
 
-	ref int
+	closing bool
+	ref     int
 	// Succeeding version.
 	next *version
 }
@@ -131,6 +132,10 @@ func (v *version) walkOverlapping(aux tFiles, ikey internalKey, f func(level int
 }
 
 func (v *version) get(aux tFiles, ikey internalKey, ro *opt.ReadOptions, noValue bool) (value []byte, tcomp bool, err error) {
+	if v.closing {
+		return nil, false, ErrClosed
+	}
+
 	ukey := ikey.ukey()
 
 	var (