release-3.5: backport #17263 Fix tx buffer inconsistency if there are…

… unordered key writes in one tx.

#17263

Notes:
1. batch_tx_test.go is not incorporated into this backport because main and release-3.5 diverges a lot on buckets/schema/etc..
It is also not the core of the bug fix.
2. verify in tx_buffer.go is removed as mainly due to the dependency is not there in relese-3.5.

Signed-off-by: Chao Chen <[email protected]>

server/mvcc/backend/tx_buffer.go

@@ -50,7 +50,8 @@ func (txw *txWriteBuffer) put(bucket Bucket, k, v []byte) {
 }
 
 func (txw *txWriteBuffer) putSeq(bucket Bucket, k, v []byte) {
-	// TODO: Add (in tests?) verification whether k>b[len(b)]
+	// putSeq is only be called for the data in the Key bucket. The keys
+	// in the Key bucket should be monotonically increasing revisions.
 	txw.putInternal(bucket, k, v)
 }
 
@@ -80,6 +81,9 @@ func (txw *txWriteBuffer) writeback(txr *txReadBuffer) {
 		rb, ok := txr.buckets[k]
 		if !ok {
 			delete(txw.buckets, k)
+			if seq, ok := txw.bucket2seq[k]; ok && !seq {
+				wb.dedupe()
+			}
 			txr.buckets[k] = wb
 			continue
 		}
@@ -148,7 +152,7 @@ func newBucketBuffer() *bucketBuffer {
 func (bb *bucketBuffer) Range(key, endKey []byte, limit int64) (keys [][]byte, vals [][]byte) {
 	f := func(i int) bool { return bytes.Compare(bb.buf[i].key, key) >= 0 }
 	idx := sort.Search(bb.used, f)
-	if idx < 0 {
+	if idx < 0 || idx >= bb.used {
 		return nil, nil
 	}
 	if len(endKey) == 0 {
@@ -201,10 +205,15 @@ func (bb *bucketBuffer) merge(bbsrc *bucketBuffer) {
 	if bytes.Compare(bb.buf[(bb.used-bbsrc.used)-1].key, bbsrc.buf[0].key) < 0 {
 		return
 	}
+	bb.dedupe()
+}
 
+// dedupe removes duplicates, using only newest update
+func (bb *bucketBuffer) dedupe() {
+	if bb.used <= 1 {
+		return
+	}
 	sort.Stable(bb)
-
-	// remove duplicates, using only newest update
 	widx := 0
 	for ridx := 1; ridx < bb.used; ridx++ {
 		if !bytes.Equal(bb.buf[ridx].key, bb.buf[widx].key) {

server/mvcc/backend/tx_buffer_test.go

@@ -0,0 +1,71 @@
+// Copyright 2023 The etcd Authors
+//
+// 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 backend
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDedupe(t *testing.T) {
+	tests := []struct {
+		name                                   string
+		keys, vals, expectedKeys, expectedVals []string
+	}{
+		{
+			name:         "empty",
+			keys:         []string{},
+			vals:         []string{},
+			expectedKeys: []string{},
+			expectedVals: []string{},
+		},
+		{
+			name:         "single kv",
+			keys:         []string{"key1"},
+			vals:         []string{"val1"},
+			expectedKeys: []string{"key1"},
+			expectedVals: []string{"val1"},
+		},
+		{
+			name:         "duplicate key",
+			keys:         []string{"key1", "key1"},
+			vals:         []string{"val1", "val2"},
+			expectedKeys: []string{"key1"},
+			expectedVals: []string{"val2"},
+		},
+		{
+			name:         "unordered keys",
+			keys:         []string{"key3", "key1", "key4", "key2", "key1", "key4"},
+			vals:         []string{"val1", "val5", "val3", "val4", "val2", "val6"},
+			expectedKeys: []string{"key1", "key2", "key3", "key4"},
+			expectedVals: []string{"val2", "val4", "val1", "val6"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			bb := &bucketBuffer{buf: make([]kv, 10), used: 0}
+			for i := 0; i < len(tt.keys); i++ {
+				bb.add([]byte(tt.keys[i]), []byte(tt.vals[i]))
+			}
+			bb.dedupe()
+			assert.Len(t, tt.expectedKeys, bb.used)
+			for i := 0; i < bb.used; i++ {
+				assert.Equal(t, bb.buf[i].key, []byte(tt.expectedKeys[i]))
+				assert.Equal(t, bb.buf[i].val, []byte(tt.expectedVals[i]))
+			}
+		})
+	}
+}