From 533c7777b9492dfe23f46d92fd60a20c4bc3e2f8 Mon Sep 17 00:00:00 2001
From: goroutine <ngaut@users.noreply.github.com>
Date: Tue, 17 Jul 2018 20:09:34 +0800
Subject: [PATCH] tablecodec: make decode much more faster (#7071)

---
 tablecodec/tablecodec.go      | 29 +++++++++++++++++++++--------
 tablecodec/tablecodec_test.go | 15 +++++++++++++++
 2 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/tablecodec/tablecodec.go b/tablecodec/tablecodec.go
index b53a3c47b10da..d1d26306d61b9 100644
--- a/tablecodec/tablecodec.go
+++ b/tablecodec/tablecodec.go
@@ -42,9 +42,11 @@ var (
 )
 
 const (
-	idLen           = 8
-	prefixLen       = 1 + idLen /*tableID*/ + 2
-	recordRowKeyLen = prefixLen + idLen /*handle*/
+	idLen                 = 8
+	prefixLen             = 1 + idLen /*tableID*/ + 2
+	recordRowKeyLen       = prefixLen + idLen /*handle*/
+	tablePrefixLength     = 1
+	recordPrefixSepLength = 2
 )
 
 // TableSplitKeyLen is the length of key 't{table_id}' which is used for table split.
@@ -84,25 +86,36 @@ func EncodeRecordKey(recordPrefix kv.Key, h int64) kv.Key {
 	return buf
 }
 
+func hasTablePrefix(key kv.Key) bool {
+	return key[0] == tablePrefix[0]
+}
+
+func hasRecordPrefixSep(key kv.Key) bool {
+	return key[0] == recordPrefixSep[0] && key[1] == recordPrefixSep[1]
+}
+
 // DecodeRecordKey decodes the key and gets the tableID, handle.
 func DecodeRecordKey(key kv.Key) (tableID int64, handle int64, err error) {
+	if len(key) <= prefixLen {
+		return 0, 0, errInvalidRecordKey.Gen("invalid record key - %q", key)
+	}
+
 	k := key
-	if !key.HasPrefix(tablePrefix) {
+	if !hasTablePrefix(key) {
 		return 0, 0, errInvalidRecordKey.Gen("invalid record key - %q", k)
 	}
 
-	key = key[len(tablePrefix):]
+	key = key[tablePrefixLength:]
 	key, tableID, err = codec.DecodeInt(key)
 	if err != nil {
 		return 0, 0, errors.Trace(err)
 	}
 
-	if !key.HasPrefix(recordPrefixSep) {
+	if !hasRecordPrefixSep(key) {
 		return 0, 0, errInvalidRecordKey.Gen("invalid record key - %q", k)
 	}
 
-	key = key[len(recordPrefixSep):]
-
+	key = key[recordPrefixSepLength:]
 	key, handle, err = codec.DecodeInt(key)
 	if err != nil {
 		return 0, 0, errors.Trace(err)
diff --git a/tablecodec/tablecodec_test.go b/tablecodec/tablecodec_test.go
index 32ad85e59ab15..a16dd291349ee 100644
--- a/tablecodec/tablecodec_test.go
+++ b/tablecodec/tablecodec_test.go
@@ -20,6 +20,7 @@ import (
 	"time"
 
 	. "github.com/pingcap/check"
+	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/mysql"
 	"github.com/pingcap/tidb/sessionctx/stmtctx"
 	"github.com/pingcap/tidb/types"
@@ -359,3 +360,17 @@ func (s *testTableCodecSuite) TestDecodeIndexKey(c *C) {
 	c.Assert(decodeIndexID, Equals, indexID)
 	c.Assert(decodeValues, DeepEquals, valueStrs)
 }
+
+func BenchmarkHasTablePrefix(b *testing.B) {
+	k := kv.Key("foobar")
+	for i := 0; i < b.N; i++ {
+		hasTablePrefix(k)
+	}
+}
+
+func BenchmarkHasTablePrefixBuiltin(b *testing.B) {
+	k := kv.Key("foobar")
+	for i := 0; i < b.N; i++ {
+		k.HasPrefix(tablePrefix)
+	}
+}