decode with value size (pingcap#1641)

Add size parameter for Decode to reduce slice growth
BenchmarkDecodeWithSize-8 300000 6153 ns/op
BenchmarkDecodeWithOutSize-8 200000 11934 ns/op

bench_test.go

@@ -1,3 +1,16 @@
+// Copyright 2016 PingCAP, Inc.
+//
+// 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,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 package tidb
 
 import (

plan/statistics/statistics.go

@@ -346,7 +346,7 @@ func TableFromPB(ti *model.TableInfo, tpb *TablePB) (*Table, error) {
 	t.Columns = make([]*Column, len(tpb.GetColumns()))
 	for i, cInfo := range t.info.Columns {
 		cpb := tpb.Columns[i]
-		values, err := codec.Decode(cpb.GetValue())
+		values, err := codec.Decode(cpb.GetValue(), 1)
 		if err != nil {
 			return nil, errors.Trace(err)
 		}

store/localstore/xapi_test.go

@@ -99,7 +99,7 @@ func (s *testXAPISuite) TestSelect(c *C) {
 	handles := make([]int, 0, 10)
 	for _, row := range idxResp.Rows {
 		var err error
-		datums, err := codec.Decode(row.Handle)
+		datums, err := codec.Decode(row.Handle, 1)
 		c.Check(err, IsNil)
 		c.Check(datums, HasLen, 1)
 		handles = append(handles, int(datums[0].GetInt64()))

table/tables/index.go

@@ -68,7 +68,7 @@ func (c *indexIter) Next() (val []types.Datum, h int64, err error) {
 	}
 	// get indexedValues
 	buf := c.it.Key()[len(c.prefix):]
-	vv, err := codec.Decode(buf)
+	vv, err := codec.Decode(buf, len(c.idx.idxInfo.Columns))
 	if err != nil {
 		return nil, 0, errors.Trace(err)
 	}

tablecodec/tablecodec.go

@@ -163,7 +163,7 @@ func DecodeValues(data []byte, fts []*types.FieldType, inIndex bool) ([]types.Da
 	if data == nil {
 		return nil, nil
 	}
-	values, err := codec.Decode(data)
+	values, err := codec.Decode(data, len(fts))
 	if err != nil {
 		return nil, errors.Trace(err)
 	}
@@ -348,7 +348,7 @@ func EncodeIndexSeekKey(tableID int64, idxID int64, encodedValue []byte) kv.Key
 // DecodeIndexKey decodes datums from an index key.
 func DecodeIndexKey(key kv.Key) ([]types.Datum, error) {
 	b := key[prefixLen+idLen:]
-	return codec.Decode(b)
+	return codec.Decode(b, 1)
 }
 
 // CutIndexKey cuts encoded index key into colIDs to bytes slices map.

util/codec/bench_test.go

@@ -0,0 +1,49 @@
+// Copyright 2016 PingCAP, Inc.
+//
+// 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,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package codec
+
+import (
+	"testing"
+
+	"github.com/pingcap/tidb/util/types"
+)
+
+var valueCnt = 100
+
+func composeEncodedData(size int) []byte {
+	values := make([]types.Datum, 0, size)
+	for i := 0; i < size; i++ {
+		values = append(values, types.NewDatum(i))
+	}
+	bs, _ := EncodeValue(nil, values...)
+	return bs
+}
+
+func BenchmarkDecodeWithSize(b *testing.B) {
+	b.StopTimer()
+	bs := composeEncodedData(valueCnt)
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		Decode(bs, valueCnt)
+	}
+}
+
+func BenchmarkDecodeWithOutSize(b *testing.B) {
+	b.StopTimer()
+	bs := composeEncodedData(valueCnt)
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		Decode(bs, 1)
+	}
+}

util/codec/codec.go

@@ -129,14 +129,15 @@ func EncodeValue(b []byte, v ...types.Datum) ([]byte, error) {
 
 // Decode decodes values from a byte slice generated with EncodeKey or EncodeValue
 // before.
-func Decode(b []byte) ([]types.Datum, error) {
+// size is the size of decoded datum slice.
+func Decode(b []byte, size int) ([]types.Datum, error) {
 	if len(b) < 1 {
 		return nil, errors.New("invalid encoded key")
 	}
 
 	var (
 		err    error
-		values = make([]types.Datum, 0, 1)
+		values = make([]types.Datum, 0, size)
 	)
 
 	for len(b) > 0 {

util/codec/codec_test.go

@@ -78,13 +78,13 @@ func (s *testCodecSuite) TestCodecKey(c *C) {
 		comment := Commentf("%d %v", i, t)
 		b, err := EncodeKey(nil, t.Input...)
 		c.Assert(err, IsNil, comment)
-		args, err := Decode(b)
+		args, err := Decode(b, 1)
 		c.Assert(err, IsNil)
 		c.Assert(args, DeepEquals, t.Expect)
 
 		b, err = EncodeValue(nil, t.Input...)
 		c.Assert(err, IsNil)
-		args, err = Decode(b)
+		args, err = Decode(b, 1)
 		c.Assert(err, IsNil)
 		c.Assert(args, DeepEquals, t.Expect)
 	}
@@ -492,7 +492,7 @@ func (s *testCodecSuite) TestTime(c *C) {
 
 		b, err := EncodeKey(nil, m)
 		c.Assert(err, IsNil)
-		v, err := Decode(b)
+		v, err := Decode(b, 1)
 		c.Assert(err, IsNil)
 		var t mysql.Time
 		t.Type = mysql.TypeDatetime
@@ -537,7 +537,7 @@ func (s *testCodecSuite) TestDuration(c *C) {
 
 		b, err := EncodeKey(nil, types.NewDatum(m))
 		c.Assert(err, IsNil)
-		v, err := Decode(b)
+		v, err := Decode(b, 1)
 		c.Assert(err, IsNil)
 		m.Fsp = mysql.MaxFsp
 		c.Assert(v, DeepEquals, types.MakeDatums(m))
@@ -592,7 +592,7 @@ func (s *testCodecSuite) TestDecimal(c *C) {
 		c.Assert(err, IsNil)
 		b, err := EncodeKey(nil, types.NewDatum(dec))
 		c.Assert(err, IsNil)
-		v, err := Decode(b)
+		v, err := Decode(b, 1)
 		c.Assert(err, IsNil)
 		c.Assert(v, HasLen, 1)
 		vv := v[0].GetMysqlDecimal()

xapi/xapi.go

@@ -184,7 +184,7 @@ func (pr *partialResult) Next() (handle int64, data []types.Datum, err error) {
 	}
 	if !pr.aggregate {
 		handleBytes := row.GetHandle()
-		datums, err := codec.Decode(handleBytes)
+		datums, err := codec.Decode(handleBytes, 1)
 		if err != nil {
 			return 0, nil, errors.Trace(err)
 		}

xapi/xeval/eval.go

@@ -530,7 +530,7 @@ func (e *Evaluator) decodeValueList(valueListExpr *tipb.Expr) (*decodedValueList
 	if decoded != nil {
 		return decoded, nil
 	}
-	list, err := codec.Decode(valueListExpr.Val)
+	list, err := codec.Decode(valueListExpr.Val, 1)
 	if err != nil {
 		return nil, errors.Trace(err)
 	}