*: reduce runtime.growslice by preallocation (pingcap#9946)

ddl/column_test.go

@@ -960,7 +960,7 @@ func (s *testColumnSuite) colDefStrToFieldType(c *C, str string) *types.FieldTyp
 func (s *testColumnSuite) TestFieldCase(c *C) {
 	var fields = []string{"field", "Field"}
 	var colDefs = make([]*ast.ColumnDef, len(fields))
-	var colObjects []interface{}
+	colObjects := make([]interface{}, 0, len(fields))
 	for i, name := range fields {
 		colDefs[i] = &ast.ColumnDef{
 			Name: &ast.ColumnName{

ddl/ddl_api.go

@@ -173,7 +173,6 @@ func setColumnFlagWithConstraint(colMap map[string]*table.Column, v *ast.Constra
 
 func buildColumnsAndConstraints(ctx sessionctx.Context, colDefs []*ast.ColumnDef,
 	constraints []*ast.Constraint, tblCharset, dbCharset string) ([]*table.Column, []*ast.Constraint, error) {
-	var cols []*table.Column
 	colMap := map[string]*table.Column{}
 	// outPriKeyConstraint is the primary key constraint out of column definition. such as: create table t1 (id int , age int, primary key(id));
 	var outPriKeyConstraint *ast.Constraint
@@ -183,6 +182,7 @@ func buildColumnsAndConstraints(ctx sessionctx.Context, colDefs []*ast.ColumnDef
 			break
 		}
 	}
+	cols := make([]*table.Column, 0, len(colDefs))
 	for i, colDef := range colDefs {
 		col, cts, err := buildColumnAndConstraint(ctx, i, colDef, outPriKeyConstraint, tblCharset, dbCharset)
 		if err != nil {
@@ -1061,7 +1061,7 @@ func BuildTableInfoFromAST(s *ast.CreateTableStmt) (*model.TableInfo, error) {
 func buildTableInfoWithCheck(ctx sessionctx.Context, d *ddl, s *ast.CreateTableStmt, dbCharset string) (*model.TableInfo, error) {
 	ident := ast.Ident{Schema: s.Table.Schema, Name: s.Table.Name}
 	colDefs := s.Cols
-	var colObjects []interface{}
+	colObjects := make([]interface{}, 0, len(colDefs))
 	for _, col := range colDefs {
 		colObjects = append(colObjects, col)
 	}
@@ -1245,7 +1245,7 @@ func (d *ddl) CreateView(ctx sessionctx.Context, s *ast.CreateViewStmt) (err err
 	}
 	viewInfo, cols := buildViewInfoWithTableColumns(ctx, s)
 
-	var colObjects []interface{}
+	colObjects := make([]interface{}, 0, len(viewInfo.Cols))
 	for _, col := range viewInfo.Cols {
 		colObjects = append(colObjects, col)
 	}

executor/builder.go

@@ -1930,7 +1930,7 @@ func (b *executorBuilder) buildWindow(v *plannercore.PhysicalWindow) *WindowExec
 		return nil
 	}
 	base := newBaseExecutor(b.ctx, v.Schema(), v.ExplainID(), childExec)
-	var groupByItems []expression.Expression
+	groupByItems := make([]expression.Expression, 0, len(v.PartitionBy))
 	for _, item := range v.PartitionBy {
 		groupByItems = append(groupByItems, item.Col)
 	}

executor/checksum.go

@@ -188,14 +188,12 @@ func newChecksumContext(db *model.DBInfo, table *model.TableInfo, startTs uint64
 }
 
 func (c *checksumContext) BuildRequests(ctx sessionctx.Context) ([]*kv.Request, error) {
-	var reqs []*kv.Request
-
+	reqs := make([]*kv.Request, 0, len(c.TableInfo.Indices)+1)
 	req, err := c.buildTableRequest(ctx)
 	if err != nil {
 		return nil, errors.Trace(err)
 	}
 	reqs = append(reqs, req)
-
 	for _, indexInfo := range c.TableInfo.Indices {
 		if indexInfo.State != model.StatePublic {
 			continue

executor/show.go

@@ -251,7 +251,7 @@ func (e *ShowExec) fetchShowTables() error {
 		return ErrBadDB.GenWithStackByArgs(e.DBName)
 	}
 	// sort for tables
-	var tableNames []string
+	tableNames := make([]string, 0, len(e.is.SchemaTables(e.DBName)))
 	var tableTypes = make(map[string]string)
 	for _, v := range e.is.SchemaTables(e.DBName) {
 		// Test with mysql.AllPrivMask means any privilege would be OK.

infoschema/tables.go

@@ -631,8 +631,8 @@ func dataForProcesslist(ctx sessionctx.Context) [][]types.Datum {
 		}
 	}
 
-	var records [][]types.Datum
 	pl := sm.ShowProcessList()
+	records := make([][]types.Datum, 0, len(pl))
 	for _, pi := range pl {
 		// If you have the PROCESS privilege, you can see all threads.
 		// Otherwise, you can see only your own threads.
@@ -704,7 +704,7 @@ var filesCols = []columnInfo{
 
 func dataForSchemata(schemas []*model.DBInfo) [][]types.Datum {
 
-	var rows [][]types.Datum
+	rows := make([][]types.Datum, 0, len(schemas))
 
 	for _, schema := range schemas {
 
@@ -1087,7 +1087,7 @@ func dataForColumns(ctx sessionctx.Context, schemas []*model.DBInfo) [][]types.D
 }
 
 func dataForColumnsInTable(schema *model.DBInfo, tbl *model.TableInfo) [][]types.Datum {
-	var rows [][]types.Datum
+	rows := make([][]types.Datum, 0, len(tbl.Columns))
 	for i, col := range tbl.Columns {
 		var charMaxLen, charOctLen, numericPrecision, numericScale, datetimePrecision interface{}
 		colLen, decimal := col.Flen, col.Decimal

meta/meta.go

@@ -677,7 +677,7 @@ func (m *Meta) GetAllHistoryDDLJobs() ([]*model.Job, error) {
 	if err != nil {
 		return nil, errors.Trace(err)
 	}
-	var jobs []*model.Job
+	jobs := make([]*model.Job, 0, len(pairs))
 	for _, pair := range pairs {
 		job := &model.Job{}
 		err = job.Decode(pair.Value)

planner/core/rule_join_elimination.go

@@ -66,7 +66,7 @@ func (o *outerJoinEliminator) tryToEliminateOuterJoin(p *LogicalJoin, aggCols []
 
 // extract join keys as a schema for inner child of a outer join
 func (o *outerJoinEliminator) extractInnerJoinKeys(join *LogicalJoin, innerChildIdx int) *expression.Schema {
-	var joinKeys []*expression.Column
+	joinKeys := make([]*expression.Column, 0, len(join.EqualConditions))
 	for _, eqCond := range join.EqualConditions {
 		joinKeys = append(joinKeys, eqCond.GetArgs()[innerChildIdx].(*expression.Column))
 	}

server/http_handler.go

@@ -1580,7 +1580,7 @@ func (h allServerInfoHandler) ServeHTTP(w http.ResponseWriter, req *http.Request
 		return
 	}
 	allVersionsMap := map[domain.ServerVersionInfo]struct{}{}
-	var allVersions []domain.ServerVersionInfo
+	allVersions := make([]domain.ServerVersionInfo, 0, len(allServersInfo))
 	for _, v := range allServersInfo {
 		if _, ok := allVersionsMap[v.ServerVersionInfo]; ok {
 			continue

server/http_handler_test.go

@@ -71,7 +71,7 @@ func (ts *HTTPHandlerTestSuite) TestRegionIndexRange(c *C) {
 		types.NewBytesDatum([]byte("foobar")),
 		types.NewFloat64Datum(-100.25),
 	}
-	var expectIndexValues []string
+	expectIndexValues := make([]string, 0, len(indexValues))
 	for _, v := range indexValues {
 		str, err := v.ToString()
 		if err != nil {

store/mockstore/mocktikv/cluster.go

@@ -417,7 +417,7 @@ func (c *Cluster) firstStoreID() uint64 {
 
 // getRegionsCoverRange gets regions in the cluster that has intersection with [start, end).
 func (c *Cluster) getRegionsCoverRange(start, end MvccKey) []*Region {
-	var regions []*Region
+	regions := make([]*Region, 0, len(c.regions))
 	for _, region := range c.regions {
 		onRight := bytes.Compare(end, region.Meta.StartKey) <= 0
 		onLeft := bytes.Compare(region.Meta.EndKey, start) <= 0

store/mockstore/mocktikv/mvcc_leveldb.go

@@ -355,7 +355,7 @@ func (mvcc *MVCCLevelDB) BatchGet(ks [][]byte, startTS uint64, isoLevel kvrpcpb.
 	mvcc.mu.RLock()
 	defer mvcc.mu.RUnlock()
 
-	var pairs []Pair
+	pairs := make([]Pair, 0, len(ks))
 	for _, k := range ks {
 		v, err := mvcc.getValue(k, startTS, isoLevel)
 		if v == nil && err == nil {
@@ -959,7 +959,7 @@ func (mvcc *MVCCLevelDB) RawBatchGet(keys [][]byte) [][]byte {
 	mvcc.mu.Lock()
 	defer mvcc.mu.Unlock()
 
-	var values [][]byte
+	values := make([][]byte, 0, len(keys))
 	for _, key := range keys {
 		value, err := mvcc.db.Get(key, nil)
 		terror.Log(err)

store/tikv/delete_range_test.go

@@ -64,8 +64,8 @@ func (s *testDeleteRangeSuite) checkData(c *C, expectedData map[string]string) {
 	c.Assert(err, IsNil)
 
 	// Print log
-	var actualKeys []string
-	var expectedKeys []string
+	actualKeys := make([]string, 0, len(data))
+	expectedKeys := make([]string, 0, len(expectedData))
 	for key := range data {
 		actualKeys = append(actualKeys, key)
 	}

store/tikv/lock_resolver.go

@@ -198,7 +198,7 @@ func (lr *LockResolver) BatchResolveLocks(bo *Backoffer, locks []*Lock, loc Regi
 		zap.Duration("cost time", time.Since(startTime)),
 		zap.Int("num of txn", len(txnInfos)))
 
-	var listTxnInfos []*kvrpcpb.TxnInfo
+	listTxnInfos := make([]*kvrpcpb.TxnInfo, 0, len(txnInfos))
 	for txnID, status := range txnInfos {
 		listTxnInfos = append(listTxnInfos, &kvrpcpb.TxnInfo{
 			Txn:    txnID,

tablecodec/tablecodec_test.go

@@ -353,7 +353,7 @@ func (s *testTableCodecSuite) TestDecodeIndexKey(c *C) {
 		// 	Type: mysql.TypeTimestamp,
 		// }),
 	}
-	var valueStrs []string
+	valueStrs := make([]string, 0, len(values))
 	for _, v := range values {
 		str, err := v.ToString()
 		if err != nil {

types/datum.go

@@ -1798,7 +1798,7 @@ func handleTruncateError(sc *stmtctx.StatementContext) error {
 
 // DatumsToString converts several datums to formatted string.
 func DatumsToString(datums []Datum, handleSpecialValue bool) (string, error) {
-	var strs []string
+	strs := make([]string, 0, len(datums))
 	for _, datum := range datums {
 		if handleSpecialValue {
 			switch datum.Kind() {