INSERT ... ON DUPLICATE during index merge phase will cause data inconsistency

[joechenrh]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Run the following test:

From 1625d2e39b71cb06d4e4724ec28c5a65f662b873 Mon Sep 17 00:00:00 2001
From: joechenrh <[email protected]>
Date: Fri, 15 Nov 2024 08:15:19 +0000
Subject: [PATCH] Add test

---
 pkg/ddl/index.go             |  1 +
 pkg/ddl/index_modify_test.go | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/pkg/ddl/index.go b/pkg/ddl/index.go
index 0a73371562..6f853f6545 100644
--- a/pkg/ddl/index.go
+++ b/pkg/ddl/index.go
@@ -1352,6 +1352,7 @@ func doReorgWorkForCreateIndex(
 				MockDMLExecutionStateBeforeMerge()
 			}
 		})
+		failpoint.InjectCall("BeforeBackfillMerge", job)
 		logutil.DDLLogger().Info("index backfill state ready to merge",
 			zap.Int64("job ID", job.ID),
 			zap.String("table", tbl.Meta().Name.O),
diff --git a/pkg/ddl/index_modify_test.go b/pkg/ddl/index_modify_test.go
index b38d05fbff..7999368ea1 100644
--- a/pkg/ddl/index_modify_test.go
+++ b/pkg/ddl/index_modify_test.go
@@ -1422,3 +1422,25 @@ func TestAddVectorIndexRollback(t *testing.T) {
 
 	testfailpoint.Disable(t, "github.com/pingcap/tidb/pkg/ddl/MockCheckVectorIndexProcess")
 }
+
+func TestAddIndex(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tkVar := testkit.NewTestKit(t, store)
+	tkVar.MustExec("set @@global.tidb_ddl_enable_fast_reorg = 1")
+	tkVar.MustExec("set @@global.tidb_enable_dist_task=0")
+
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t (col1 int, col2 int, unique index i1(col2) /*T![global_index] GLOBAL */) PARTITION BY HASH (col1) PARTITIONS 2")
+
+	tk2 := testkit.NewTestKit(t, store)
+	tk2.MustExec("use test")
+
+	testfailpoint.EnableCall(t, "github.com/pingcap/tidb/pkg/ddl/BeforeBackfillMerge", func(job *model.Job) {
+		tk2.MustExec("insert ignore into t values (1, 2), (1, 2) on duplicate key update col1 = 0, col2 = 0")
+	})
+	defer testfailpoint.Disable(t, "github.com/pingcap/tidb/pkg/ddl/BeforeBackfillMerge")
+
+	tk.MustExec("alter table t add unique index i(col1, col2)")
+	tk.MustExec("admin check table t")
+}
-- 
2.43.0

2. What did you expect to see? (Required)

Test passed.

3. What did you see instead (Required)

admin check table failed.

4. What is your TiDB version? (Required)

[joechenrh]

/severity major

[joechenrh]

/remove-label may-affects-5.4
/remove-label may-affects-6.1
/remove-label may-affects-6.5
/remove-label may-affects-7.1
/remove-label may-affects-7.5
/remove-label may-affects-8.1
/remove-label may-affects-8.5