large overestimation when where conditions contain OR and matches several indexes with different selectivity

[time-and-fate]

Reproduce

create table t(a int, b int, c int, d int, index iabc(a,b,c), index ib(b));

-- run this many times
insert into t value (rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000, rand()*10, rand()*1000, rand()*1000);

-- run this many times
insert into t select * from t;

analyze table t;

explain analyze select * from t where (a = 1 and b = 1 and c = 1) or (a = 2 and b = 2 and c = 2) or (a = 3 and b = 3 and c = 3);
explain analyze select * from t use index (iabc) where (a = 1 and b = 1 and c = 1) or (a = 2 and b = 2 and c = 2) or (a = 3 and b = 3 and c = 3);

There is a big overestimation

> explain analyze select * from t where (a = 1 and b = 1 and c = 1) or (a = 2 and b = 2 and c = 2) or (a = 3 and b = 3 and c = 3);
+-------------------------+----------+---------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------+------+
| id                      | estRows  | actRows | task      | access object | execution info                                                                                                                                                                                                                                                                                                                                                                                  | operator info                                                                                                                                                                                 | memory    | disk |
+-------------------------+----------+---------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------+------+
| TableReader_7           | 7014.40  | 0       | root      |               | time:36.3ms, loops:1, RU:36.071812, cop_task: {num: 1, max: 36.2ms, proc_keys: 29440, tot_proc: 35.2ms, tot_wait: 70.6µs, copr_cache_hit_ratio: 0.00, build_task_duration: 10.9µs, max_distsql_concurrency: 1}, rpc_info:{Cop:{num_rpc:1, total_time:36.1ms}}                                                                                                                                   | data:Selection_6                                                                                                                                                                              | 289 Bytes | N/A  |
| └─Selection_6           | 7014.40  | 0       | cop[tikv] |               | tikv_task:{time:37ms, loops:33}, scan_detail: {total_process_keys: 29440, total_process_keys_size: 1564192, total_keys: 29441, get_snapshot_time: 27.9µs, rocksdb: {delete_skipped_count: 28520, key_skipped_count: 57960, block: {}}}, time_detail: {total_process_time: 35.2ms, total_suspend_time: 202µs, total_wait_time: 70.6µs, total_kv_read_wall_time: 27ms, tikv_wall_time: 35.7ms}    | or(and(eq(test.t.a, 1), and(eq(test.t.b, 1), eq(test.t.c, 1))), or(and(eq(test.t.a, 2), and(eq(test.t.b, 2), eq(test.t.c, 2))), and(eq(test.t.a, 3), and(eq(test.t.b, 3), eq(test.t.c, 3))))) | N/A       | N/A  |
|   └─TableFullScan_5     | 29440.00 | 29440   | cop[tikv] | table:t       | tikv_task:{time:27ms, loops:33}                                                                                                                                                                                                                                                                                                                                                                 | keep order:false                                                                                                                                                                              | N/A       | N/A  |
+-------------------------+----------+---------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------+------+
3 rows in set (0.04 sec)

> explain analyze select * from t use index (iabc) where (a = 1 and b = 1 and c = 1) or (a = 2 and b = 2 and c = 2) or (a = 3 and b = 3 and c = 3);
+-------------------------------+---------+---------+-----------+------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------------------------------+-----------+------+
| id                            | estRows | actRows | task      | access object                | execution info                                                                                                                                                                                                                                                                                                                                                                                                                                                 | operator info                                                       | memory    | disk |
+-------------------------------+---------+---------+-----------+------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------------------------------+-----------+------+
| IndexLookUp_7                 | 8768.00 | 0       | root      |                              | time:762.9µs, loops:1, RU:0.496309                                                                                                                                                                                                                                                                                                                                                                                                                             |                                                                     | 257 Bytes | N/A  |
| ├─IndexRangeScan_5(Build)     | 8768.00 | 0       | cop[tikv] | table:t, index:iabc(a, b, c) | time:607.9µs, loops:1, cop_task: {num: 1, max: 532.8µs, proc_keys: 0, tot_proc: 63.9µs, tot_wait: 47.2µs, copr_cache_hit_ratio: 0.00, build_task_duration: 28.2µs, max_distsql_concurrency: 1}, rpc_info:{Cop:{num_rpc:1, total_time:509.9µs}}, tikv_task:{time:0s, loops:1}, scan_detail: {total_keys: 3, get_snapshot_time: 24µs, rocksdb: {block: {}}}, time_detail: {total_process_time: 63.9µs, total_wait_time: 47.2µs, tikv_wall_time: 206µs}           | range:[1 1 1,1 1 1], [2 2 2,2 2 2], [3 3 3,3 3 3], keep order:false | N/A       | N/A  |
| └─TableRowIDScan_6(Probe)     | 8768.00 | 0       | cop[tikv] | table:t                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                | keep order:false                                                    | N/A       | N/A  |
+-------------------------------+---------+---------+-----------+------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------------------------------+-----------+------+