*: check delete unique key's handle to handle corner case

pkg/ddl/index.go

@@ -875,6 +875,11 @@ func doReorgWorkForCreateIndex(w *worker, d *ddlCtx, t *meta.Meta, job *model.Jo
 		ver, err = updateVersionAndTableInfo(d, t, job, tbl.Meta(), true)
 		return false, ver, errors.Trace(err)
 	case model.BackfillStateReadyToMerge:
+		failpoint.Inject("mockDMLExecutionStateBeforeMerge", func(_ failpoint.Value) {
+			if MockDMLExecutionStateBeforeMerge != nil {
+				MockDMLExecutionStateBeforeMerge()
+			}
+		})
 		logutil.DDLLogger().Info("index backfill state ready to merge",
 			zap.Int64("job ID", job.ID),
 			zap.String("table", tbl.Meta().Name.O),
@@ -1924,6 +1929,9 @@ var MockDMLExecutionStateMerging func()
 // MockDMLExecutionStateBeforeImport is only used for test.
 var MockDMLExecutionStateBeforeImport func()
 
+// MockDMLExecutionStateBeforeMerge is only used for test.
+var MockDMLExecutionStateBeforeMerge func()
+
 func (w *worker) addPhysicalTableIndex(t table.PhysicalTable, reorgInfo *reorgInfo) error {
 	if reorgInfo.mergingTmpIdx {
 		logutil.DDLLogger().Info("start to merge temp index", zap.Stringer("job", reorgInfo.Job), zap.Stringer("reorgInfo", reorgInfo))

pkg/ddl/ingest/backend.go

@@ -41,6 +41,9 @@ import (
 	"go.uber.org/zap"
 )
 
+// MockDMLExecutionStateBeforeImport is a failpoint to mock the DML execution state before import.
+var MockDMLExecutionStateBeforeImport func()
+
 // BackendCtx is the backend context for one add index reorg task.
 type BackendCtx interface {
 	// Register create a new engineInfo for each index ID and register it to the
@@ -237,6 +240,11 @@ func (bc *litBackendCtx) Flush(mode FlushMode) (flushed, imported bool, errIdxID
 			}
 		}()
 	}
+	failpoint.Inject("mockDMLExecutionStateBeforeImport", func(_ failpoint.Value) {
+		if MockDMLExecutionStateBeforeImport != nil {
+			MockDMLExecutionStateBeforeImport()
+		}
+	})
 
 	for indexID, ei := range bc.engines {
 		if err = bc.unsafeImportAndReset(ei); err != nil {

pkg/table/tables/index.go

@@ -427,9 +427,28 @@ func (c *index) Delete(ctx table.MutateContext, txn kv.Transaction, indexedValue
 
 		if distinct {
 			if len(key) > 0 {
-				err = txn.GetMemBuffer().DeleteWithFlags(key, kv.SetNeedLocked)
-				if err != nil {
-					return err
+				okToDelete := true
+				if c.idxInfo.BackfillState != model.BackfillStateInapplicable {
+					// #52914: the delete key is covered by the new ingested key, which shouldn't be deleted.
+					originVal, err := getKeyInTxn(context.TODO(), txn, key)
+					if err != nil {
+						return err
+					}
+					if len(originVal) > 0 {
+						oh, err := tablecodec.DecodeHandleInUniqueIndexValue(originVal, c.tblInfo.IsCommonHandle)
+						if err != nil {
+							return err
+						}
+						if !h.Equal(oh) {
+							okToDelete = false
+						}
+					}
+				}
+				if okToDelete {
+					err = txn.GetMemBuffer().DeleteWithFlags(key, kv.SetNeedLocked)
+					if err != nil {
+						return err
+					}
 				}
 			}
 			if len(tempKey) > 0 {

tests/realtikvtest/addindextest/BUILD.bazel

@@ -13,10 +13,15 @@ go_test(
     ],
     deps = [
         "//pkg/config",
+        "//pkg/ddl",
         "//pkg/ddl/ingest",
+        "//pkg/ddl/util/callback",
+        "//pkg/parser/model",
         "//pkg/testkit",
         "//tests/realtikvtest",
         "//tests/realtikvtest/addindextestutil",
+        "@com_github_pingcap_failpoint//:failpoint",
+        "@com_github_stretchr_testify//assert",
         "@com_github_stretchr_testify//require",
         "@com_github_tikv_client_go_v2//tikv",
     ],

tests/realtikvtest/addindextest/add_index_test.go

@@ -20,11 +20,16 @@ import (
 	"path/filepath"
 	"testing"
 
+	"github.com/pingcap/failpoint"
 	"github.com/pingcap/tidb/pkg/config"
+	"github.com/pingcap/tidb/pkg/ddl"
 	"github.com/pingcap/tidb/pkg/ddl/ingest"
+	"github.com/pingcap/tidb/pkg/ddl/util/callback"
+	"github.com/pingcap/tidb/pkg/parser/model"
 	"github.com/pingcap/tidb/pkg/testkit"
 	"github.com/pingcap/tidb/tests/realtikvtest"
 	"github.com/pingcap/tidb/tests/realtikvtest/addindextestutil"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"github.com/tikv/client-go/v2/tikv"
 )
@@ -200,3 +205,52 @@ func TestLitBackendCtxMgr(t *testing.T) {
 	_, ok = mgr.Load(jobID)
 	require.False(t, ok)
 }
+
+func TestAddUniqueDuplicateIndexes(t *testing.T) {
+	store, dom := realtikvtest.CreateMockStoreAndDomainAndSetup(t)
+
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t(a int DEFAULT '-13202', b varchar(221) NOT NULL DEFAULT 'duplicatevalue', " +
+		"c int NOT NULL DEFAULT '0');")
+
+	tk1 := testkit.NewTestKit(t, store)
+	tk1.MustExec("use test")
+
+	d := dom.DDL()
+	originalCallback := d.GetHook()
+	defer d.SetHook(originalCallback)
+	callback := &callback.TestDDLCallback{}
+
+	tk1.Exec("INSERT INTO t VALUES (-18585,'duplicatevalue',0);")
+
+	onJobUpdatedExportedFunc := func(job *model.Job) {
+		switch job.SchemaState {
+		case model.StateDeleteOnly:
+			_, err := tk1.Exec("delete from t where c = 0;")
+			assert.NoError(t, err)
+			_, err = tk1.Exec("insert INTO t VALUES (-18585,'duplicatevalue',1);")
+			assert.NoError(t, err)
+		}
+	}
+	callback.OnJobUpdatedExported.Store(&onJobUpdatedExportedFunc)
+	d.SetHook(callback)
+
+	tk3 := testkit.NewTestKit(t, store)
+	tk3.MustExec("use test")
+	ingest.MockDMLExecutionStateBeforeImport = func() {
+		tk3.MustExec("replace INTO t VALUES (-18585,'duplicatevalue',4);")
+		tk3.MustQuery("select * from t;").Check(testkit.Rows("-18585 duplicatevalue 1", "-18585 duplicatevalue 4"))
+	}
+	ddl.MockDMLExecutionStateBeforeMerge = func() {
+		tk3.MustQuery("select * from t;").Check(testkit.Rows("-18585 duplicatevalue 1", "-18585 duplicatevalue 4"))
+		tk3.MustExec("replace into t values (-18585,'duplicatevalue',0);")
+	}
+
+	require.NoError(t, failpoint.Enable("github.com/pingcap/tidb/pkg/ddl/ingest/mockDMLExecutionStateBeforeImport", "1*return"))
+	require.NoError(t, failpoint.Enable("github.com/pingcap/tidb/pkg/ddl/mockDMLExecutionStateBeforeMerge", "return(true)"))
+	tk.MustExec("alter table t add unique index idx(b);")
+	tk.MustExec("admin check table t;")
+	require.NoError(t, failpoint.Disable("github.com/pingcap/tidb/pkg/ddl/ingest/mockDMLExecutionStateBeforeImport"))
+	require.NoError(t, failpoint.Disable("github.com/pingcap/tidb/pkg/ddl/mockDMLExecutionStateBeforeMerge"))
+}