diff --git a/server/mvcc/backend/backend.go b/server/mvcc/backend/backend.go
index 055aedaff..dde78b603 100644
--- a/server/mvcc/backend/backend.go
+++ b/server/mvcc/backend/backend.go
@@ -511,7 +511,7 @@ func defragdb(odb, tmpdb *bolt.DB, limit int) error {
 		if berr != nil {
 			return berr
 		}
-		tmpb.FillPercent = 0.9 // for seq write in for each
+		tmpb.FillPercent = 0.9 // for bucket2seq write in for each
 
 		if err = b.ForEach(func(k, v []byte) error {
 			count++
@@ -525,7 +525,7 @@ func defragdb(odb, tmpdb *bolt.DB, limit int) error {
 					return err
 				}
 				tmpb = tmptx.Bucket(next)
-				tmpb.FillPercent = 0.9 // for seq write in for each
+				tmpb.FillPercent = 0.9 // for bucket2seq write in for each
 
 				count = 0
 			}
diff --git a/server/mvcc/backend/batch_tx.go b/server/mvcc/backend/batch_tx.go
index 74107b445..358b47615 100644
--- a/server/mvcc/backend/batch_tx.go
+++ b/server/mvcc/backend/batch_tx.go
@@ -253,8 +253,8 @@ func newBatchTxBuffered(backend *backend) *batchTxBuffered {
 	tx := &batchTxBuffered{
 		batchTx: batchTx{backend: backend},
 		buf: txWriteBuffer{
-			txBuffer: txBuffer{make(map[string]*bucketBuffer)},
-			seq:      true,
+			txBuffer:   txBuffer{make(map[string]*bucketBuffer)},
+			bucket2seq: make(map[string]bool),
 		},
 	}
 	tx.Commit()
diff --git a/server/mvcc/backend/tx_buffer.go b/server/mvcc/backend/tx_buffer.go
index 4df6d0c59..78844e94a 100644
--- a/server/mvcc/backend/tx_buffer.go
+++ b/server/mvcc/backend/tx_buffer.go
@@ -37,23 +37,44 @@ func (txb *txBuffer) reset() {
 // txWriteBuffer buffers writes of pending updates that have not yet committed.
 type txWriteBuffer struct {
 	txBuffer
-	seq bool
+	// Map from bucket name into information whether this bucket is edited
+	// sequentially (i.e. keys are growing monotonically).
+	bucket2seq map[string]bool
 }
 
+// TODO: Passing bucket as an (int) enum would avoid a lot of byte[]->string->hash conversions.
 func (txw *txWriteBuffer) put(bucket, k, v []byte) {
-	txw.seq = false
-	txw.putSeq(bucket, k, v)
+	bucketstr := string(bucket)
+	txw.bucket2seq[bucketstr] = false
+	txw.putInternal(bucketstr, k, v)
 }
 
 func (txw *txWriteBuffer) putSeq(bucket, k, v []byte) {
-	b, ok := txw.buckets[string(bucket)]
+	// TODO: Add (in tests?) verification whether k>b[len(b)]
+	txw.putInternal(string(bucket), k, v)
+}
+
+func (txw *txWriteBuffer) putInternal(bucket string, k, v []byte) {
+	b, ok := txw.buckets[bucket]
 	if !ok {
 		b = newBucketBuffer()
-		txw.buckets[string(bucket)] = b
+		txw.buckets[bucket] = b
 	}
 	b.add(k, v)
 }
 
+func (txw *txWriteBuffer) reset() {
+	txw.txBuffer.reset()
+	for k := range txw.bucket2seq {
+		v, ok := txw.buckets[k]
+		if !ok {
+			delete(txw.bucket2seq, k)
+		} else if v.used == 0 {
+			txw.bucket2seq[k] = true
+		}
+	}
+}
+
 func (txw *txWriteBuffer) writeback(txr *txReadBuffer) {
 	for k, wb := range txw.buckets {
 		rb, ok := txr.buckets[k]
@@ -62,7 +83,7 @@ func (txw *txWriteBuffer) writeback(txr *txReadBuffer) {
 			txr.buckets[k] = wb
 			continue
 		}
-		if !txw.seq && wb.used > 1 {
+		if seq, ok := txw.bucket2seq[k]; ok && !seq && wb.used > 1 {
 			// assume no duplicate keys
 			sort.Sort(wb)
 		}