build, backend: add backend commit failpoints

build

@@ -12,7 +12,7 @@ fi
 
 # enable/disable failpoints
 toggle_failpoints() {
-	FAILPKGS="etcdserver/"
+	FAILPKGS="etcdserver/ mvcc/backend/"
 
 	mode="disable"
 	if [ ! -z "$FAILPOINTS" ]; then mode="enable"; fi

mvcc/backend/batch_tx.go

@@ -166,7 +166,9 @@ func (t *batchTx) commit(stop bool) {
 			return
 		}
 		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)