server: optimize com_field_list, make use database faster. (#5677)

server/driver_tidb.go

@@ -22,7 +22,6 @@ import (
 	"github.com/pingcap/tidb/ast"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/mysql"
-	"github.com/pingcap/tidb/terror"
 	"github.com/pingcap/tidb/util"
 	"github.com/pingcap/tidb/util/auth"
 	"github.com/pingcap/tidb/util/types"
@@ -230,19 +229,16 @@ func (tc *TiDBContext) Auth(user *auth.UserIdentity, auth []byte, salt []byte) b
 }
 
 // FieldList implements QueryCtx FieldList method.
-func (tc *TiDBContext) FieldList(table string) (colums []*ColumnInfo, err error) {
-	rs, err := tc.Execute("SELECT * FROM `" + table + "` LIMIT 0")
-	if len(rs) > 0 {
-		defer terror.Call(rs[0].Close)
-	}
+func (tc *TiDBContext) FieldList(table string) (columns []*ColumnInfo, err error) {
+	fields, err := tc.session.FieldList(table)
 	if err != nil {
 		return nil, errors.Trace(err)
 	}
-	colums, err = rs[0].Columns()
-	if err != nil {
-		return nil, errors.Trace(err)
+	columns = make([]*ColumnInfo, 0, len(fields))
+	for _, f := range fields {
+		columns = append(columns, convertColumnInfo(f))
 	}
-	return
+	return columns, nil
 }
 
 // GetStatement implements QueryCtx GetStatement method.

server/tidb_test.go

@@ -401,3 +401,72 @@ func (ts *TidbTestSuite) TestShowCreateTableFlen(c *C) {
 	c.Assert(int(cols[0].ColumnLength), Equals, 5*tmysql.MaxBytesOfCharacter)
 	c.Assert(int(cols[1].ColumnLength), Equals, len(row[1].GetString())*tmysql.MaxBytesOfCharacter)
 }
+
+func checkColNames(c *C, columns []*ColumnInfo, names ...string) {
+	for i, name := range names {
+		c.Assert(columns[i].Name, Equals, name)
+		c.Assert(columns[i].OrgName, Equals, name)
+	}
+}
+
+func (ts *TidbTestSuite) TestFieldList(c *C) {
+	ctx, err := ts.tidbdrv.OpenCtx(uint64(0), 0, uint8(tmysql.DefaultCollationID), "test", nil)
+	c.Assert(err, IsNil)
+	_, err = ctx.Execute("use test;")
+	c.Assert(err, IsNil)
+
+	testSQL := `create table t (
+		c_bit bit(10),
+		c_int_d int,
+		c_bigint_d bigint,
+		c_float_d float,
+		c_double_d double,
+		c_decimal decimal(6, 3),
+		c_datetime datetime(2),
+		c_time time(3),
+		c_date date,
+		c_timestamp timestamp(4) DEFAULT CURRENT_TIMESTAMP(4),
+		c_char char(20),
+		c_varchar varchar(20),
+		c_text_d text,
+		c_binary binary(20),
+		c_blob_d blob,
+		c_set set('a', 'b', 'c'),
+		c_enum enum('a', 'b', 'c'),
+		c_json JSON,
+		c_year year
+	)`
+	_, err = ctx.Execute(testSQL)
+	c.Assert(err, IsNil)
+	colInfos, err := ctx.FieldList("t")
+	c.Assert(err, IsNil)
+	c.Assert(len(colInfos), Equals, 19)
+
+	checkColNames(c, colInfos, "c_bit", "c_int_d", "c_bigint_d", "c_float_d",
+		"c_double_d", "c_decimal", "c_datetime", "c_time", "c_date", "c_timestamp",
+		"c_char", "c_varchar", "c_text_d", "c_binary", "c_blob_d", "c_set", "c_enum",
+		"c_json", "c_year")
+
+	for _, cols := range colInfos {
+		c.Assert(cols.Schema, Equals, "test")
+	}
+
+	for _, cols := range colInfos {
+		c.Assert(cols.Table, Equals, "t")
+	}
+
+	for i, col := range colInfos {
+		switch i {
+		case 10, 11, 12, 15, 16:
+			// c_char char(20), c_varchar varchar(20), c_text_d text,
+			// c_set set('a', 'b', 'c'), c_enum enum('a', 'b', 'c')
+			c.Assert(col.Charset, Equals, uint16(tmysql.CharsetIDs["utf8"]), Commentf("index %d", i))
+			continue
+		}
+
+		c.Assert(col.Charset, Equals, uint16(tmysql.CharsetIDs["binary"]), Commentf("index %d", i))
+	}
+
+	// c_decimal decimal(6, 3)
+	c.Assert(colInfos[5].Decimal, Equals, uint8(3))
+}

session.go

@@ -36,6 +36,7 @@ import (
 	"github.com/pingcap/tidb/executor"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/meta"
+	"github.com/pingcap/tidb/model"
 	"github.com/pingcap/tidb/mysql"
 	"github.com/pingcap/tidb/parser"
 	"github.com/pingcap/tidb/plan/cache"
@@ -84,6 +85,8 @@ type Session interface {
 	ShowProcess() util.ProcessInfo
 	// PrePareTxnCtx is exported for test.
 	PrepareTxnCtx()
+	// FieldList returns fields list of a table.
+	FieldList(tableName string) (fields []*ast.ResultField, err error)
 }
 
 var (
@@ -219,6 +222,31 @@ func (s *session) GetSessionManager() util.SessionManager {
 	return s.sessionManager
 }
 
+// FieldList returns fields list of a table.
+func (s *session) FieldList(tableName string) ([]*ast.ResultField, error) {
+	is := executor.GetInfoSchema(s)
+	dbName := model.NewCIStr(s.GetSessionVars().CurrentDB)
+	tName := model.NewCIStr(tableName)
+	table, err := is.TableByName(dbName, tName)
+	if err != nil {
+		return nil, errors.Trace(err)
+	}
+
+	cols := table.Cols()
+	fields := make([]*ast.ResultField, 0, len(cols))
+	for _, col := range table.Cols() {
+		rf := &ast.ResultField{
+			ColumnAsName: col.Name,
+			TableAsName:  tName,
+			DBName:       dbName,
+			Table:        table.Meta(),
+			Column:       col.ColumnInfo,
+		}
+		fields = append(fields, rf)
+	}
+	return fields, nil
+}
+
 type schemaLeaseChecker struct {
 	domain.SchemaValidator
 	schemaVer       int64