fix edge case for watermark when index is zero

watermark_edge_test.go

@@ -0,0 +1,119 @@
+/*
+ * Copyright 2023 Dgraph Labs, Inc. and Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package badger
+
+import (
+ "crypto/rand"
+ "errors"
+ "fmt"
+ "math/big"
+ "sync"
+ "testing"
+ "time"
+)
+
+func TestWaterMarkEdgeCase(t *testing.T) {
+ const N = 1_000
+ runBadgerTest(t, nil, func(t *testing.T, db *DB) {
+ eg := make(chan error, N)
+ defer close(eg)
+
+ var wg sync.WaitGroup
+ wg.Add(N)
+ for i := 0; i < N; i++ {
+ go func(j int) {
+ defer wg.Done()
+ if err := doWork(db, j); errors.Is(err, ErrConflict) {
+ eg <- nil
+ } else {
+ eg <- fmt.Errorf("expected conflict not found, err: %v, i = %v", err, j)
+ }
+ }(i)
+ }
+ wg.Wait()
+
+ for i := 0; i < N; i++ {
+ if err := <-eg; err != nil {
+ t.Fatal(err)
+ }
+ }
+ })
+}
+
+func doWork(db *DB, i int) error {
+ delay()
+
+ key1 := fmt.Sprintf("v:%d:%s", i, generateRandomBytes())
+ key2 := fmt.Sprintf("v:%d:%s", i, generateRandomBytes())
+
+ tx1 := db.NewTransaction(true)
+ defer tx1.Discard()
+ tx2 := db.NewTransaction(true)
+ defer tx2.Discard()
+
+ getValue(tx2, key1)
+ getValue(tx2, key2)
+ getValue(tx1, key1)
+ getValue(tx2, key1)
+ setValue(tx2, key1, "value1")
+ setValue(tx2, key2, "value2")
+
+ if err := tx2.Commit(); err != nil {
+ return fmt.Errorf("tx2 failed: %w (key1 = %s, key2 = %s)", err, key1, key2)
+ }
+
+ setValue(tx1, key1, "value1-second")
+ getValue(tx1, key1)
+ setValue(tx1, key1, "value1-third")
+
+ delay()
+ if err := tx1.Commit(); err != nil {
+ return fmt.Errorf("tx1 failed: %w (key1 = %s, key2 = %s)", err, key1, key2)
+ }
+
+ return nil
+}
+
+func generateRandomBytes() []byte {
+ b := make([]byte, 20)
+ if _, err := rand.Read(b); err != nil {
+ panic(err)
+ }
+ return b
+}
+
+func getValue(txn *Txn, key string) {
+ if _, err := txn.Get([]byte(key)); err != nil {
+ if !errors.Is(err, ErrKeyNotFound) {
+ panic(err)
+ }
+ }
+}
+
+func setValue(txn *Txn, key, value string) {
+ if err := txn.Set([]byte(key), []byte(value)); err != nil {
+ panic(err)
+ }
+}
+
+func delay() {
+ jitter, err := rand.Int(rand.Reader, big.NewInt(100))
+ if err != nil {
+ panic(err)
+ }
+ <-time.After(time.Duration(jitter.Int64()) * time.Millisecond)
+}

y/watermark.go

@@ -228,7 +228,8 @@ func (w *WaterMark) process(closer *z.Closer) {
  }
  }
  } else {
- if mark.index > 0 {
+ // it is possible that mark.index is zero. We need to handle that case as well.
+ if mark.index > 0 || (mark.index == 0 && len(mark.indices) == 0) {
  processOne(mark.index, mark.done)
  }
  for _, index := range mark.indices {