diff --git a/server/mvcc/backend/tx_buffer.go b/server/mvcc/backend/tx_buffer.go
index db766219f..8f95e5831 100644
--- a/server/mvcc/backend/tx_buffer.go
+++ b/server/mvcc/backend/tx_buffer.go
@@ -37,10 +37,11 @@ func (txb *txBuffer) reset() {
 // txWriteBuffer buffers writes of pending updates that have not yet committed.
 type txWriteBuffer struct {
 	txBuffer
+	// Map from bucket name into information whether this bucket is edited
+	// sequentially (i.e. keys are growing monotonically).
 	seq map[string]bool
 }
 
-
 func (txw *txWriteBuffer) put(bucket, k, v []byte) {
 	txw.seq[string(bucket)] = false
 	txw.putSeq(bucket, k, v)