TiDB can not update stats correctly after reorg some partitions

[0xPoe]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. Create a table: create table pt(a int, b varchar(10), index idx_b (b)) partition by range(a) (partition p0 values less than (10), partition p1 values less than (20), partition p2 values less than (30));
2. Insert some data: insert into pt values (1, "a"), (11, "b"), (21, "c");
3. Check the meta:

mysql> select * from mysql.stats_meta;
+--------------------+----------+--------------+-------+----------+
| version            | table_id | modify_count | count | snapshot |
+--------------------+----------+--------------+-------+----------+
| 445359109485625359 |      103 |            1 |     1 |        0 |
| 445359109485625364 |      104 |            1 |     1 |        0 |
| 445359109485625349 |      105 |            1 |     1 |        0 |
| 445359109485625364 |      102 |            3 |     3 |        0 |
+--------------------+----------+--------------+-------+----------+
4 rows in set (0.00 sec)

4. Reorg partition p0 and p1. Merge p0 and p1 into pw: alter table pt reorganize partition p0, p1 into (partition pw values less than (20));
5. Check the meta again:

mysql> select * from mysql.stats_meta;
+--------------------+----------+--------------+-------+----------+
| version            | table_id | modify_count | count | snapshot |
+--------------------+----------+--------------+-------+----------+
| 445359109485625359 |      103 |            1 |     1 |        0 |
| 445359109485625364 |      104 |            1 |     1 |        0 |
| 445359109485625349 |      105 |            1 |     1 |        0 |
| 445359109485625364 |      102 |            3 |     3 |        0 |
| 445359172675436552 |      107 |            0 |     0 |        0 |
+--------------------+----------+--------------+-------+----------+
5 rows in set (0.00 sec)

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

mysql> select * from mysql.stats_meta;
+--------------------+----------+--------------+-------+----------+
| version            | table_id | modify_count | count | snapshot |
+--------------------+----------+--------------+-------+----------+
-| 445359109485625359 |      103 |            1 |     1 |        0 |
-| 445359109485625364 |      104 |            1 |     1 |        0 |
| 445359109485625349 |      105 |            1 |     1 |        0 |
| 445359109485625364 |      102 |            3 |     3 |        0 |
+| 445359172675436552 |      107 |            2 |     2 |        0 |
+--------------------+----------+--------------+-------+----------+
5 rows in set (0.00 sec)

3. What did you see instead (Required)

mysql> select * from mysql.stats_meta;
+--------------------+----------+--------------+-------+----------+
| version            | table_id | modify_count | count | snapshot |
+--------------------+----------+--------------+-------+----------+
| 445359109485625359 |      103 |            1 |     1 |        0 |
| 445359109485625364 |      104 |            1 |     1 |        0 |
| 445359109485625349 |      105 |            1 |     1 |        0 |
| 445359109485625364 |      102 |            3 |     3 |        0 |
| 445359172675436552 |      107 |            0 |     0 |        0 |
+--------------------+----------+--------------+-------+----------+
5 rows in set (0.00 sec)

4. What is your TiDB version? (Required)

mysql> select tidb_version();
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                      |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v7.6.0-alpha-69-gbf8c728934
Edition: Community
Git Commit Hash: bf8c728934c7376765ddd943fd302fcb65af4bf0
Git Branch: master
UTC Build Time: 2023-11-01 08:29:41
GoVersion: go1.21.1
Race Enabled: false
Check Table Before Drop: false
Store: tikv |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)