From d72adf893a138cbab83e464039f33b34ecfa03ea Mon Sep 17 00:00:00 2001
From: xiaodong-ji <xiaodong.ji@outlook.com>
Date: Wed, 23 Sep 2020 14:56:38 +0800
Subject: [PATCH] DDL: Reduce the impact on DML when executing partition DDL
 (#19991)

---
 ddl/db_partition_test.go | 16 ++++++++++++++++
 ddl/ddl_worker.go        | 16 ++++++++++++++++
 infoschema/builder.go    | 11 ++++++++++-
 3 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/ddl/db_partition_test.go b/ddl/db_partition_test.go
index 701a0a3780..098b64d131 100644
--- a/ddl/db_partition_test.go
+++ b/ddl/db_partition_test.go
@@ -2204,6 +2204,22 @@ func (s *testIntegrationSuite3) TestPartitionErrorCode(c *C) {
 	tk.MustGetErrCode("alter table t_part rebuild partition p0,p1;", tmysql.ErrUnsupportedDDLOperation)
 	tk.MustGetErrCode("alter table t_part remove partitioning;", tmysql.ErrUnsupportedDDLOperation)
 	tk.MustGetErrCode("alter table t_part repair partition p1;", tmysql.ErrUnsupportedDDLOperation)
+
+	// Reduce the impact on DML when executing partition DDL
+	tk1 := testkit.NewTestKit(c, s.store)
+	tk1.MustExec("use test")
+	tk1.MustExec("drop table if exists t;")
+	tk1.MustExec(`create table t(id int primary key)
+		partition by hash(id) partitions 4;`)
+	tk1.MustExec("begin")
+	tk1.MustExec("insert into t values(1);")
+
+	tk2 := testkit.NewTestKit(c, s.store)
+	tk2.MustExec("use test")
+	tk2.MustExec("alter table t truncate partition p0;")
+
+	_, err = tk1.Exec("commit")
+	c.Assert(err, IsNil)
 }
 
 func (s *testIntegrationSuite5) TestConstAndTimezoneDepent(c *C) {
diff --git a/ddl/ddl_worker.go b/ddl/ddl_worker.go
index 62bf3d9e59..3e858d8a2d 100644
--- a/ddl/ddl_worker.go
+++ b/ddl/ddl_worker.go
@@ -865,6 +865,22 @@ func updateSchemaVersion(t *meta.Meta, job *model.Job) (int64, error) {
 			OldTableID: ptTableID,
 		}
 		diff.AffectedOpts = affects
+	case model.ActionTruncateTablePartition:
+		var oldIDs []int64
+		err = job.DecodeArgs(&oldIDs)
+		if err != nil {
+			return 0, errors.Trace(err)
+		}
+		diff.TableID = job.TableID
+		affects := make([]*model.AffectedOption, len(oldIDs))
+		for i := 0; i < len(oldIDs); i++ {
+			affects[i] = &model.AffectedOption{
+				SchemaID:   job.SchemaID,
+				TableID:    oldIDs[i],
+				OldTableID: oldIDs[i],
+			}
+		}
+		diff.AffectedOpts = affects
 	default:
 		diff.TableID = job.TableID
 	}
diff --git a/infoschema/builder.go b/infoschema/builder.go
index 6416c6f226..b40b696a04 100644
--- a/infoschema/builder.go
+++ b/infoschema/builder.go
@@ -119,6 +119,13 @@ func (b *Builder) ApplyDiff(m *meta.Meta, diff *model.SchemaDiff) ([]int64, erro
 	}
 	if diff.AffectedOpts != nil {
 		for _, opt := range diff.AffectedOpts {
+			// Reduce the impact on DML when executing partition DDL. eg.
+			// While session 1 performs the DML operation associated with partition 1,
+			// the TRUNCATE operation of session 2 on partition 2 does not cause the operation of session 1 to fail.
+			if diff.Type == model.ActionTruncateTablePartition {
+				tblIDs = append(tblIDs, opt.OldTableID)
+				continue
+			}
 			var err error
 			affectedDiff := &model.SchemaDiff{
 				Version:     diff.Version,
@@ -263,7 +270,9 @@ func (b *Builder) applyCreateTable(m *meta.Meta, dbInfo *model.DBInfo, tableID i
 			fmt.Sprintf("(Table ID %d)", tableID),
 		)
 	}
-	affected = appendAffectedIDs(affected, tblInfo)
+	if tp != model.ActionTruncateTablePartition {
+		affected = appendAffectedIDs(affected, tblInfo)
+	}
 
 	// Failpoint check whether tableInfo should be added to repairInfo.
 	// Typically used in repair table test to load mock `bad` tableInfo into repairInfo.