non-DXF ADD INDEX of large table (trigger import due to disk quota) will write KV with TS = 0

[lance6716]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

use this diff to trigger disk quota import on small tables

diff --git a/pkg/ddl/ingest/backend.go b/pkg/ddl/ingest/backend.go
index f11849f70b..cd08ec14c5 100644
--- a/pkg/ddl/ingest/backend.go
+++ b/pkg/ddl/ingest/backend.go
@@ -187,6 +187,8 @@ func (bc *litBackendCtx) Flush(indexID int64, mode FlushMode) (flushed, imported
        }

        shouldFlush, shouldImport := bc.checkFlush(mode)
+       shouldFlush = true
+       shouldImport = true
        if !shouldFlush {
                return false, false, nil
        }

and print TS used in import, or check TiKV

run TestAddIndexRemoteDuplicateCheck with the change, or other ADD INDEX that can trigger disk-quota import

diff --git a/tests/realtikvtest/addindextest4/ingest_test.go b/tests/realtikvtes
t/addindextest4/ingest_test.go
index 2e393ce4f8..7a3f91f031 100644
--- a/tests/realtikvtest/addindextest4/ingest_test.go
+++ b/tests/realtikvtest/addindextest4/ingest_test.go
@@ -407,7 +407,8 @@ func TestAddIndexRemoteDuplicateCheck(t *testing.T) {
        tk.MustExec("insert into t values(100000, 1, 1);")

        ingest.ForceSyncFlagForTest = true
-       tk.MustGetErrCode("alter table t add unique index idx(b);", errno.ErrDupEntry)
+       tk.MustExec("alter table t add index idx_test(b);")
+       //tk.MustGetErrCode("alter table t add unique index idx(b);", errno.ErrDupEntry)
        ingest.ForceSyncFlagForTest = false

        tk.MustExec("set global tidb_ddl_reorg_worker_cnt=4;")

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

no error

3. What did you see instead (Required)

TiKV panic due to it has data with TS = 0

4. What is your TiDB version? (Required)