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fix edge case for watermark when index is zero
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Fixes #1962

We have assumed that index won't be zero for a WaterMark but in
badger's unmanaged mode we start transactions with readTs = 0.
This affects oracle.readMark that could have values starting at 0.
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mangalaman93 committed Aug 29, 2023
1 parent 340ba1a commit 296ae1c
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Showing 2 changed files with 121 additions and 1 deletion.
119 changes: 119 additions & 0 deletions watermark_edge_test.go
Original file line number Diff line number Diff line change
@@ -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)
}
3 changes: 2 additions & 1 deletion y/watermark.go
Original file line number Diff line number Diff line change
Expand Up @@ -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 {
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