This is an automated cherry-pick of pingcap#43271

Signed-off-by: ti-chi-bot <ti-community-prow-bot@tidb.io>

ddl/db_partition_test.go

@@ -1478,6 +1478,39 @@ func TestAlterTableTruncatePartitionByListColumns(t *testing.T) {
 	tk.MustQuery("select * from t").Check(testkit.Rows())
 }
 
+func TestAlterTableTruncatePartitionPreSplitRegion(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	atomic.StoreUint32(&ddl.EnableSplitTableRegion, 1)
+	tk.MustExec("set @@global.tidb_scatter_region=1;")
+	tk.MustExec("use test;")
+
+	tk.MustExec("drop table if exists t1;")
+	tk.MustExec(`CREATE TABLE t1 (id int, c varchar(128), key c(c)) partition by range (id) (
+		partition p0 values less than (10), 
+		partition p1 values less than MAXVALUE)`)
+	re := tk.MustQuery("show table t1 regions")
+	rows := re.Rows()
+	require.Len(t, rows, 2)
+	tk.MustExec(`alter table t1 truncate partition p0`)
+	re = tk.MustQuery("show table t1 regions")
+	rows = re.Rows()
+	require.Len(t, rows, 2)
+
+	tk.MustExec("drop table if exists t2;")
+	tk.MustExec(`CREATE TABLE t2(id bigint(20) NOT NULL AUTO_INCREMENT, PRIMARY KEY (id) NONCLUSTERED) SHARD_ROW_ID_BITS=4 PRE_SPLIT_REGIONS=3 PARTITION BY RANGE (id) (
+		PARTITION p1 VALUES LESS THAN (10),
+		PARTITION p2 VALUES LESS THAN (20),
+		PARTITION p3 VALUES LESS THAN (MAXVALUE))`)
+	re = tk.MustQuery("show table t2 regions")
+	rows = re.Rows()
+	require.Len(t, rows, 24)
+	tk.MustExec(`alter table t2 truncate partition p3`)
+	re = tk.MustQuery("show table t2 regions")
+	rows = re.Rows()
+	require.Len(t, rows, 24)
+}
+
 func TestCreateTableWithKeyPartition(t *testing.T) {
 	store, clean := testkit.CreateMockStore(t)
 	defer clean()

ddl/ddl_api.go

@@ -3752,30 +3752,35 @@ func (d *ddl) TruncateTablePartition(ctx sessionctx.Context, ident ast.Ident, sp
 		return errors.Trace(dbterror.ErrPartitionMgmtOnNonpartitioned)
 	}
 
-	var pids []int64
-	if spec.OnAllPartitions {
-		pids = make([]int64, len(meta.GetPartitionInfo().Definitions))
-		for i, def := range meta.GetPartitionInfo().Definitions {
-			pids[i] = def.ID
+	getTruncatedParts := func(pi *model.PartitionInfo) (*model.PartitionInfo, error) {
+		if spec.OnAllPartitions {
+			return pi.Clone(), nil
 		}
-	} else {
+		var defs []model.PartitionDefinition
 		// MySQL allows duplicate partition names in truncate partition
 		// so we filter them out through a hash
-		pidMap := make(map[int64]bool)
+		posMap := make(map[int]bool)
 		for _, name := range spec.PartitionNames {
-			pid, err := tables.FindPartitionByName(meta, name.L)
-			if err != nil {
-				return errors.Trace(err)
+			pos := pi.FindPartitionDefinitionByName(name.L)
+			if pos < 0 {
+				return nil, errors.Trace(table.ErrUnknownPartition.GenWithStackByArgs(name.L, ident.Name.O))
+			}
+			if _, ok := posMap[pos]; !ok {
+				defs = append(defs, pi.Definitions[pos])
+				posMap[pos] = true
 			}
-			pidMap[pid] = true
-		}
-		// linter makezero does not handle changing pids to zero length,
-		// so create a new var and then assign to pids...
-		newPids := make([]int64, 0, len(pidMap))
-		for pid := range pidMap {
-			newPids = append(newPids, pid)
 		}
-		pids = newPids
+		pi = pi.Clone()
+		pi.Definitions = defs
+		return pi, nil
+	}
+	pi, err := getTruncatedParts(meta.GetPartitionInfo())
+	if err != nil {
+		return err
+	}
+	pids := make([]int64, 0, len(pi.Definitions))
+	for i := range pi.Definitions {
+		pids = append(pids, pi.Definitions[i].ID)
 	}
 
 	job := &model.Job{
@@ -3789,11 +3794,21 @@ func (d *ddl) TruncateTablePartition(ctx sessionctx.Context, ident ast.Ident, sp
 	}
 
 	err = d.DoDDLJob(ctx, job)
+	err = d.callHookOnChanged(job, err)
 	if err != nil {
 		return errors.Trace(err)
 	}
+<<<<<<< HEAD
 	err = d.callHookOnChanged(err)
 	return errors.Trace(err)
+=======
+	if _, tb, err := d.getSchemaAndTableByIdent(ctx, ident); err == nil {
+		if p, err := getTruncatedParts(tb.Meta().GetPartitionInfo()); err == nil {
+			d.preSplitAndScatter(ctx, tb.Meta(), p)
+		}
+	}
+	return nil
+>>>>>>> 3e4538da5d0 (partition: fix split and scatter region for truncate partition (#43271))
 }
 
 func (d *ddl) DropTablePartition(ctx sessionctx.Context, ident ast.Ident, spec *ast.AlterTableSpec) error {