server: optimizing memory overhead of copy operation in ConcurrentRea…

…dTxn

Signed-off-by: new-dream <111836360+new-dream@users.noreply.github.com>

server/storage/backend/tx_buffer.go

@@ -17,6 +17,8 @@ package backend
 import (
  "bytes"
  "sort"
+
+ "go.etcd.io/etcd/client/pkg/v3/verify"
 )
 
 const bucketBufferInitialSize = 512
@@ -124,7 +126,7 @@ func (txr *txReadBuffer) unsafeCopy() txReadBuffer {
  bufVersion: 0,
  }
  for bucketName, bucket := range txr.txBuffer.buckets {
- txrCopy.txBuffer.buckets[bucketName] = bucket.Copy()
+ txrCopy.txBuffer.buckets[bucketName] = bucket.CopyUsed()
  }
  return txrCopy
 }
@@ -221,11 +223,13 @@ func (bb *bucketBuffer) Less(i, j int) bool {
 }
 func (bb *bucketBuffer) Swap(i, j int) { bb.buf[i], bb.buf[j] = bb.buf[j], bb.buf[i] }
 
-func (bb *bucketBuffer) Copy() *bucketBuffer {
+func (bb *bucketBuffer) CopyUsed() *bucketBuffer {
+ verify.Assert(bb.used <= len(bb.buf),
+ "used (%d) should never be bigger than the length of buf (%d)", bb.used, len(bb.buf))
  bbCopy := bucketBuffer{
- buf: make([]kv, len(bb.buf)),
+ buf: make([]kv, bb.used),
  used: bb.used,
  }
- copy(bbCopy.buf, bb.buf)
+ copy(bbCopy.buf, bb.buf[:bb.used])
  return &bbCopy
 }

server/storage/backend/tx_buffer_test.go

@@ -0,0 +1,92 @@
+// 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 (
+ "fmt"
+ "testing"
+
+ "github.com/stretchr/testify/assert"
+)
+
+func Test_bucketBuffer_CopyUsed_After_Add(t *testing.T) {
+ bb := &bucketBuffer{buf: make([]kv, 10), used: 0}
+ for i := 0; i < 20; i++ {
+ k := fmt.Sprintf("key%d", i)
+ v := fmt.Sprintf("val%d", i)
+ bb.add([]byte(k), []byte(v))
+ bbCopy := bb.CopyUsed()
+ assert.Equal(t, bb.used, bbCopy.used)
+ assert.Equal(t, bbCopy.used, len(bbCopy.buf))
+ assert.GreaterOrEqual(t, len(bb.buf), len(bbCopy.buf))
+ }
+}
+
+func Test_bucketBuffer_CopyUsed(t *testing.T) {
+ tests := []struct {
+ name string
+ bufLen int
+ used int
+ wantPanic bool
+ wantUsed int
+ wantBufLen int
+ }{
+ {
+ name: "used is 0",
+ bufLen: 10,
+ used: 0,
+ wantPanic: false,
+ wantUsed: 0,
+ wantBufLen: 0,
+ },
+ {
+ name: "used is greater than 0 and less than len(buf)",
+ bufLen: 10,
+ used: 5,
+ wantPanic: false,
+ wantUsed: 5,
+ wantBufLen: 5,
+ },
+ {
+ name: "used is equal to len(buf)",
+ bufLen: 10,
+ used: 10,
+ wantPanic: false,
+ wantUsed: 10,
+ wantBufLen: 10,
+ },
+ {
+ name: "used is greater than len(buf)",
+ bufLen: 10,
+ used: 11,
+ wantPanic: true,
+ },
+ }
+
+ for _, tt := range tests {
+ t.Run(tt.name, func(t *testing.T) {
+ bb := &bucketBuffer{buf: make([]kv, tt.bufLen), used: tt.used}
+ if tt.wantPanic {
+ assert.Panicsf(t, func() {
+ bb.CopyUsed()
+ }, "expected panic when used (%d) and the length of buf (%d)", tt.used, tt.bufLen)
+ } else {
+ bbCopy := bb.CopyUsed()
+ assert.Equal(t, tt.wantUsed, bbCopy.used)
+ assert.Equal(t, tt.wantBufLen, len(bbCopy.buf))
+ }
+ })
+ }
+}