table partition: set tidb_enable_exchange_partition default on

ddl/db_partition_test.go

@@ -1861,11 +1861,6 @@ func TestAlterTableExchangePartition(t *testing.T) {
 		id INT NOT NULL
 	);`)
 	tk.MustExec(`INSERT INTO e VALUES (1669),(337),(16),(2005)`)
-	// test disable exchange partition
-	tk.MustExec("ALTER TABLE e EXCHANGE PARTITION p0 WITH TABLE e2")
-	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 8200 Exchange Partition is disabled, please set 'tidb_enable_exchange_partition' if you need to need to enable it"))
-	tk.MustQuery("select * from e").Check(testkit.Rows("16", "1669", "337", "2005"))
-	tk.MustQuery("select * from e2").Check(testkit.Rows())
 
 	// enable exchange partition
 	tk.MustExec("set @@tidb_enable_exchange_partition=1")
@@ -2440,6 +2435,35 @@ func TestExchangePartitionAutoID(t *testing.T) {
 	tk.MustQuery("select count(*) from pt where a >= 4000000").Check(testkit.Rows("1"))
 }
 
+func TestTiDBEnableExchangePartition(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+
+	tk.MustExec("use test")
+	tk.MustExec(`create table pt (a int primary key auto_increment) partition by range(a) (
+		partition p0 values less than (3),
+		partition p1 values less than (6),
+        PARTITION p2 values less than (9)
+		);`)
+	// default
+	tk.MustExec(`create table nt(a int primary key auto_increment);`)
+	tk.MustExec("alter table pt exchange partition p0 with table nt")
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1105 after the exchange, please analyze related table of the exchange to update statistics"))
+
+	// set tidb_enable_exchange_partition = 0
+	tk.MustExec("set @@tidb_enable_exchange_partition=0")
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1105 tidb_enable_exchange_partition is always turned on, this variable will be deleted later"))
+	tk.MustExec("alter table pt exchange partition p0 with table nt")
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1105 after the exchange, please analyze related table of the exchange to update statistics"))
+
+	// set tidb_enable_exchange_partition = 1
+	tk.MustExec("set @@tidb_enable_exchange_partition=1")
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1105 tidb_enable_exchange_partition is always turned on, this variable will be deleted later"))
+	tk.MustExec("alter table pt exchange partition p0 with table nt")
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1105 after the exchange, please analyze related table of the exchange to update statistics"))
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1105 after the exchange, please analyze related table of the exchange to update statistics"))
+}
+
 func TestExchangePartitionExpressIndex(t *testing.T) {
 	restore := config.RestoreFunc()
 	defer restore()

ddl/ddl_api.go

@@ -3981,10 +3981,6 @@ func checkExchangePartition(pt *model.TableInfo, nt *model.TableInfo) error {
 }
 
 func (d *ddl) ExchangeTablePartition(ctx sessionctx.Context, ident ast.Ident, spec *ast.AlterTableSpec) error {
-	if !ctx.GetSessionVars().TiDBEnableExchangePartition {
-		ctx.GetSessionVars().StmtCtx.AppendWarning(dbterror.ErrExchangePartitionDisabled)
-		return nil
-	}
 	ptSchema, pt, err := d.getSchemaAndTableByIdent(ctx, ident)
 	if err != nil {
 		return errors.Trace(err)

ddl/placement_policy_test.go

@@ -2060,8 +2060,7 @@ func TestPDFail(t *testing.T) {
 	checkAllBundlesNotChange(t, existBundles)
 
 	// exchange partition
-	tk.MustExec("alter table tp exchange partition p1 with table t1")
-	require.True(t, infosync.ErrHTTPServiceError.Equal(err))
+	tk.MustGetErrCode("alter table tp exchange partition p1 with table t1", mysql.ErrTablesDifferentMetadata)
 	tk.MustQuery("show create table t1").Check(testkit.Rows("t1 CREATE TABLE `t1` (\n" +
 		"  `id` int(11) DEFAULT NULL\n" +
 		") ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin"))

sessionctx/variable/sysvar.go

@@ -1607,7 +1607,8 @@ var defaultSysVars = []*SysVar{
 		return nil
 	}},
 	{Scope: ScopeGlobal | ScopeSession, Name: TiDBEnableExchangePartition, Value: BoolToOnOff(DefTiDBEnableExchangePartition), Type: TypeBool, SetSession: func(s *SessionVars, val string) error {
-		s.TiDBEnableExchangePartition = TiDBOptOn(val)
+		s.StmtCtx.AppendWarning(errors.New("tidb_enable_exchange_partition is always turned on, this variable will be deleted later"))
+		s.TiDBEnableExchangePartition = true
 		return nil
 	}},
 	// It's different from tmp_table_size or max_heap_table_size. See https://github.com/pingcap/tidb/issues/28691.

sessionctx/variable/tidb_vars.go

@@ -947,7 +947,7 @@ const (
 	DefTiDBAnalyzeVersion                          = 2
 	DefTiDBEnableIndexMergeJoin                    = false
 	DefTiDBTrackAggregateMemoryUsage               = true
-	DefTiDBEnableExchangePartition                 = false
+	DefTiDBEnableExchangePartition                 = true
 	DefCTEMaxRecursionDepth                        = 1000
 	DefTiDBTmpTableMaxSize                         = 64 << 20 // 64MB.
 	DefTiDBEnableLocalTxn                          = false