mvcc/backend: clean up mutex, logging

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

mvcc/backend/batch_tx.go

@@ -136,15 +136,15 @@ func unsafeForEach(tx *bolt.Tx, bucket []byte, visitor func(k, v []byte) error)
 // Commit commits a previous tx and begins a new writable one.
 func (t *batchTx) Commit() {
 	t.Lock()
-	defer t.Unlock()
 	t.commit(false)
+	t.Unlock()
 }
 
 // CommitAndStop commits the previous tx and does not create a new one.
 func (t *batchTx) CommitAndStop() {
 	t.Lock()
-	defer t.Unlock()
 	t.commit(true)
+	t.Unlock()
 }
 
 func (t *batchTx) Unlock() {
@@ -162,9 +162,11 @@ func (t *batchTx) commit(stop bool) {
 		}
 
 		start := time.Now()
+
 		// gofail: var beforeCommit struct{}
 		err := t.tx.Commit()
 		// gofail: var afterCommit struct{}
+
 		commitDurations.Observe(time.Since(start).Seconds())
 		atomic.AddInt64(&t.backend.commits, 1)
 
@@ -209,21 +211,21 @@ func (t *batchTxBuffered) Unlock() {
 
 func (t *batchTxBuffered) Commit() {
 	t.Lock()
-	defer t.Unlock()
 	t.commit(false)
+	t.Unlock()
 }
 
 func (t *batchTxBuffered) CommitAndStop() {
 	t.Lock()
-	defer t.Unlock()
 	t.commit(true)
+	t.Unlock()
 }
 
 func (t *batchTxBuffered) commit(stop bool) {
 	// all read txs must be closed to acquire boltdb commit rwlock
 	t.backend.readTx.mu.Lock()
-	defer t.backend.readTx.mu.Unlock()
 	t.unsafeCommit(stop)
+	t.backend.readTx.mu.Unlock()
 }
 
 func (t *batchTxBuffered) unsafeCommit(stop bool) {