Cannot use IndexMerge in transaction

[guo-shaoge]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

drop table if exists t1;
create table t1(c1 int, c2 int, key(c1), key(c2));
begin;
explain select /*+ use_index_merge(t1) */ * from t1 where c1 < 10 or c2 < 10;
insert into t1 values(1, 1);
explain select /*+ use_index_merge(t1) */ * from t1 where c1 < 10 or c2 < 10;
commit; 

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

By using hint, we can use IndexMerge

3. What did you see instead (Required)

 MySQL [test]>     explain select /*+ use_index_merge(t1) */ * from t1 where c1 < 10 or c2 < 10;
+-------------------------------+---------+-----------+------------------------+-------------------------------------------------+
| id                            | estRows | task      | access object          | operator info                                   |
+-------------------------------+---------+-----------+------------------------+-------------------------------------------------+
| IndexMerge_8                  | 5542.21 | root      |                        |                                                 |
| ├─IndexRangeScan_5(Build) | 3323.33 | cop[tikv] | table:t1, index:c1(c1) | range:[-inf,10), keep order:false, stats:pseudo |
| ├─IndexRangeScan_6(Build) | 3323.33 | cop[tikv] | table:t1, index:c2(c2) | range:[-inf,10), keep order:false, stats:pseudo |
| └─TableRowIDScan_7(Probe) | 5542.21 | cop[tikv] | table:t1               | keep order:false, stats:pseudo                  |
+-------------------------------+---------+-----------+------------------------+-------------------------------------------------+
4 rows in set (0.01 sec)

MySQL [test]>     insert into t1 values(1, 1);
Query OK, 1 row affected (0.00 sec)

MySQL [test]>     explain select /*+ use_index_merge(t1) */ * from t1 where c1 < 10 or c2 < 10;
+-----------------------------+----------+-----------+---------------+--------------------------------------------+
| id                          | estRows  | task      | access object | operator info                              |
+-----------------------------+----------+-----------+---------------+--------------------------------------------+
| Projection_5                | 5542.21  | root      |               | test.t1.c1, test.t1.c2                     |
| └─UnionScan_6           | 5542.21  | root      |               | or(lt(test.t1.c1, 10), lt(test.t1.c2, 10)) |
|   └─TableReader_9       | 5542.21  | root      |               | data:Selection_8                           |
|     └─Selection_8       | 5542.21  | cop[tikv] |               | or(lt(test.t1.c1, 10), lt(test.t1.c2, 10)) |
|       └─TableFullScan_7 | 10000.00 | cop[tikv] | table:t1      | keep order:false, stats:pseudo             |
+-----------------------------+----------+-----------+---------------+--------------------------------------------+
5 rows in set, 1 warning (0.00 sec)

4. What is your TiDB version? (Required)

mysql> select tidb_version();
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()
|
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v5.4.0-alpha-140-g68b5e0658c
Edition: Community
Git Commit Hash: 68b5e06
Git Branch: index_merge
UTC Build Time: 2021-11-18 07:12:21
GoVersion: go1.16.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)