*: enable tidb_enable_foreign_key variable default

br/tests/br_foreign_key/run.sh

@@ -17,7 +17,6 @@
 set -eu
 DB="$TEST_NAME"
 
-run_sql "set @@global.tidb_enable_foreign_key=1;"
 run_sql "set @@global.foreign_key_checks=1;"
 run_sql "set @@foreign_key_checks=1;"
 run_sql "create schema $DB;"

cmd/explaintest/r/explain_foreign_key.result

@@ -1,4 +1,3 @@
-set @@global.tidb_enable_foreign_key=1;
 set @@foreign_key_checks=1;
 use test;
 drop table if exists t1,t2;
@@ -165,5 +164,4 @@ Delete	N/A	root		N/A
   └─TableReader(Probe)	3333.33	root		data:TableRangeScan
     └─TableRangeScan	3333.33	cop[tikv]	table:t_1	range:(0,+inf], keep order:true, stats:pseudo
 drop table if exists t_1,t_2,t_3,t_4;
-set @@global.tidb_enable_foreign_key=0;
 set @@foreign_key_checks=0;

cmd/explaintest/t/explain_foreign_key.test

@@ -1,4 +1,3 @@
-set @@global.tidb_enable_foreign_key=1;
 set @@foreign_key_checks=1;
 use test;
 drop table if exists t1,t2;
@@ -43,5 +42,4 @@ set @@foreign_key_checks=0;
 explain format = 'brief' update t_1,t_2 set t_1.id=2,t_2.id=2 where t_1.id=t_2.id and t_1.id=1;
 explain format = 'brief' delete t_1,t_2 from t_1 join t_2 where t_1.id=t_2.id and t_1.id > 0;
 drop table if exists t_1,t_2,t_3,t_4;
-set @@global.tidb_enable_foreign_key=0;
 set @@foreign_key_checks=0;

ddl/db_table_test.go

@@ -51,7 +51,7 @@ func TestTableForeignKey(t *testing.T) {
 	store := testkit.CreateMockStore(t)
 	tk := testkit.NewTestKit(t, store)
 	tk.MustExec("use test")
-	tk.MustExec("create table t1 (a int, b int);")
+	tk.MustExec("create table t1 (a int, b int, index(a), index(b));")
 	// test create table with foreign key.
 	failSQL := "create table t2 (c int, foreign key (a) references t1(a));"
 	tk.MustGetErrCode(failSQL, errno.ErrKeyColumnDoesNotExits)

ddl/foreign_key_test.go

@@ -28,6 +28,7 @@ import (
 	"github.com/pingcap/tidb/sessiontxn"
 	"github.com/pingcap/tidb/table"
 	"github.com/pingcap/tidb/testkit"
+	"github.com/pingcap/tidb/types"
 	"github.com/stretchr/testify/require"
 )
 
@@ -107,7 +108,17 @@ func TestForeignKey(t *testing.T) {
 	testCreateSchema(t, testkit.NewTestKit(t, store).Session(), dom.DDL(), dbInfo)
 	tblInfo, err := testTableInfo(store, "t", 3)
 	require.NoError(t, err)
-
+	tblInfo.Indices = append(tblInfo.Indices, &model.IndexInfo{
+		ID:    1,
+		Name:  model.NewCIStr("idx_fk"),
+		Table: model.NewCIStr("t"),
+		Columns: []*model.IndexColumn{&model.IndexColumn{
+			Name:   model.NewCIStr("c1"),
+			Offset: 0,
+			Length: types.UnspecifiedLength,
+		}},
+		State: model.StatePublic,
+	})
 	testCreateTable(t, testkit.NewTestKit(t, store).Session(), d, dbInfo, tblInfo)
 
 	// fix data race

executor/fktest/foreign_key_test.go

@@ -1969,6 +1969,7 @@ func TestShowCreateTableWithForeignKey(t *testing.T) {
 	tk := testkit.NewTestKit(t, store)
 	tk.MustExec("use test")
 
+	tk.MustExec("set @@global.tidb_enable_foreign_key=0")
 	tk.MustExec("create table t1 (id int key, leader int, leader2 int, index(leader), index(leader2), constraint fk foreign key (leader) references t1(id) ON DELETE CASCADE ON UPDATE SET NULL);")
 	tk.MustQuery("show create table t1").Check(testkit.Rows("t1 CREATE TABLE `t1` (\n" +
 		"  `id` int(11) NOT NULL,\n" +

sessionctx/variable/sysvar.go

@@ -1249,7 +1249,7 @@ var defaultSysVars = []*SysVar{
 		}
 		return normalizedValue, ErrWrongValueForVar.GenWithStackByArgs(ForeignKeyChecks, originalValue)
 	}},
-	{Scope: ScopeGlobal, Name: TiDBEnableForeignKey, Value: BoolToOnOff(false), Type: TypeBool, SetGlobal: func(_ context.Context, s *SessionVars, val string) error {
+	{Scope: ScopeGlobal, Name: TiDBEnableForeignKey, Value: BoolToOnOff(true), Type: TypeBool, SetGlobal: func(_ context.Context, s *SessionVars, val string) error {
 		EnableForeignKey.Store(TiDBOptOn(val))
 		return nil
 	}, GetGlobal: func(_ context.Context, s *SessionVars) (string, error) {

sessionctx/variable/tidb_vars.go

@@ -1185,7 +1185,7 @@ var (
 	// DDLDiskQuota is the temporary variable for set disk quota for lightning
 	DDLDiskQuota = atomic.NewUint64(DefTiDBDDLDiskQuota)
 	// EnableForeignKey indicates whether to enable foreign key feature.
-	EnableForeignKey    = atomic.NewBool(false)
+	EnableForeignKey    = atomic.NewBool(true)
 	EnableRCReadCheckTS = atomic.NewBool(false)
 
 	// DefTiDBServerMemoryLimit indicates the default value of TiDBServerMemoryLimit(TotalMem * 80%).