tidb: Plan binding evolution rejecting improved plans

Description

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Consider the following test case:

DROP TABLE IF EXISTS t1;
CREATE TABLE t1 (
 pk VARBINARY(36) NOT NULL PRIMARY KEY,
 b BIGINT NOT NULL,
 c BIGINT NOT NULL,
 pad VARBINARY(2048),
 INDEX (b)
);
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM dual;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT uuid(), FLOOR(RAND()*5), FLOOR(RAND()*1000000), HEX(RANDOM_BYTES(1000)) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
SELECT SLEEP(2);
ANALYZE TABLE t1;
SELECT SLEEP(2);

SELECT * FROM t1 WHERE b = 2 AND c = 123412;
SELECT * FROM t1 WHERE b = 3 AND c = 392812;
SELECT * FROM t1 WHERE b = 4 AND c = 932932;
DROP GLOBAL BINDING FOR SELECT * FROM t1 WHERE b = 3 AND c = 321210; -- drop incase this example is run twice
SHOW GLOBAL BINDINGS;
ADMIN CAPTURE BINDINGS;
SHOW GLOBAL BINDINGS;

EXPLAIN SELECT * FROM t1 WHERE b = 4 AND c = 3921228;
ALTER TABLE t1 ADD INDEX (c);
SELECT SLEEP(2);
ANALYZE TABLE t1;
SELECT SLEEP(2);
EXPLAIN SELECT * FROM t1 WHERE b = 1 AND c = 275628;

SELECT SLEEP(10); -- allow background work from alter table etc to settle

SET tidb_evolve_plan_baselines = 1;
SELECT SLEEP(2);
SELECT * FROM t1 WHERE b = 2 AND c = 3924541;

SHOW GLOBAL BINDINGS;
SELECT SLEEP(1);
SHOW GLOBAL BINDINGS;
SELECT SLEEP(10);
SHOW GLOBAL BINDINGS;

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

The new plan is faster, and should be accepted. Here is the output from EXPLAIN ANALYZE:

mysql> explain analyze SELECT /*+ use_index(@`sel_1` `test`.`t1` `b`)*/ * FROM `t1` WHERE `b`=2 AND `c`=123412;
+-------------------------------+-----------+---------+-----------+----------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------+----------------------+------+
| id                            | estRows   | actRows | task      | access object        | execution info                                                                                                                             | operator info                 | memory               | disk |
+-------------------------------+-----------+---------+-----------+----------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------+----------------------+------+
| IndexLookUp_8                 | 0.20      | 0       | root      |                      | time:457.133993ms, loops:1, cop_task: {num: 1, max:495.556µs, proc_keys: 0, rpc_num: 1, rpc_time: 469.706µs, copr_cache_hit_ratio: 1.00}   |                               | 6.245874404907227 MB | N/A  |
| ├─IndexRangeScan_5(Build)     | 128139.00 | 128389  | cop[tikv] | table:t1, index:b(b) | time:52ms, loops:130                                                                                                                       | range:[2,2], keep order:false | N/A                  | N/A  |
| └─Selection_7(Probe)          | 0.20      | 0       | cop[tikv] |                      | time:0ns, loops:0                                                                                                                          | eq(test.t1.c, 123412)         | N/A                  | N/A  |
|   └─TableRowIDScan_6          | 128139.00 | 0       | cop[tikv] | table:t1             | time:0ns, loops:0                                                                                                                          | keep order:false              | N/A                  | N/A  |
+-------------------------------+-----------+---------+-----------+----------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------+----------------------+------+
4 rows in set (0.46 sec)

mysql> explain analyze SELECT /*+ use_index(@`sel_1` `test`.`t1` `c`)*/ * FROM `test`.`t1` WHERE `b`=2 AND `c`=3924541;
+-------------------------------+---------+---------+-----------+----------------------+------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------+-----------+------+
| id                            | estRows | actRows | task      | access object        | execution info                                                                                                                           | operator info                             | memory    | disk |
+-------------------------------+---------+---------+-----------+----------------------+------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------+-----------+------+
| IndexLookUp_8                 | 0.00    | 0       | root      |                      | time:706.484µs, loops:1, cop_task: {num: 1, max:595.214µs, proc_keys: 0, rpc_num: 1, rpc_time: 564.225µs, copr_cache_hit_ratio: 0.00}    |                                           | 185 Bytes | N/A  |
| ├─IndexRangeScan_5(Build)     | 0.00    | 0       | cop[tikv] | table:t1, index:c(c) | time:0s, loops:1                                                                                                                         | range:[3924541,3924541], keep order:false | N/A       | N/A  |
| └─Selection_7(Probe)          | 0.00    | 0       | cop[tikv] |                      | time:0ns, loops:0                                                                                                                        | eq(test.t1.b, 2)                          | N/A       | N/A  |
|   └─TableRowIDScan_6          | 0.00    | 0       | cop[tikv] | table:t1             | time:0ns, loops:0                                                                                                                        | keep order:false                          | N/A       | N/A  |
+-------------------------------+---------+---------+-----------+----------------------+------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------+-----------+------+
4 rows in set (0.00 sec)

3. What did you see instead (Required)

The new plan is rejected:

mysql> SHOW GLOBAL BINDINGS\G
*************************** 1. row ***************************
Original_sql: select * from t1 where b = ? and c = ?
    Bind_sql: SELECT /*+ use_index(@`sel_1` `test`.`t1` `b`)*/ * FROM `t1` WHERE `b`=2 AND `c`=123412
  Default_db: test
      Status: using
 Create_time: 2020-10-12 14:50:09.461
 Update_time: 2020-10-12 14:50:09.461
     Charset: 
   Collation: 
      Source: capture
*************************** 2. row ***************************
Original_sql: select * from t1 where b = ? and c = ?
    Bind_sql: SELECT /*+ use_index(@`sel_1` `test`.`t1` `c`)*/ * FROM `test`.`t1` WHERE `b`=2 AND `c`=3924541
  Default_db: test
      Status: rejected
 Create_time: 2020-10-12 14:50:52.311
 Update_time: 2020-10-12 14:50:55.311
     Charset: utf8
   Collation: utf8_general_ci
      Source: evolve
2 rows in set (0.00 sec)

4. What is your TiDB version? (Required)

mysql> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v4.0.0-beta.2-1357-g38ecab6a7
Edition: Community
Git Commit Hash: 38ecab6a7c1dde3c9a2ed2713b3a69d63f662b77
Git Branch: master
UTC Build Time: 2020-10-12 12:52:19
GoVersion: go1.13
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.00 sec)

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Score

Mentor

@lzmhhh123

About this issue

Original URL
State: closed
Created 4 years ago
Comments: 17 (10 by maintainers)

Most upvoted comments

OK, I finally made it to understand the root cause. Here is a minimal repro:

CREATE TABLE t1 (
 pk VARBINARY(36) NOT NULL PRIMARY KEY,
 b BIGINT NOT NULL,
 c BIGINT NOT NULL,
 pad VARBINARY(2048),
 INDEX (b),
 INDEX (c)
);

MySQL [test]> create global binding for select * from t1 WHERE b=2 AND c=3924541 using select /*+ use_index(@sel_1 test.t1 b) */ * from t1 WHERE b=2 AND c=3924541;
Query OK, 0 rows affected (0.01 sec)

MySQL [test]> explain SELECT /*+ use_index(@`sel_1` `test`.`t1` `c`)*/ * FROM `test`.`t1` WHERE `b`=2 AND `c`=3924541;
+-------------------------------+---------+-----------+----------------------+---------------------------------------------------------+
| id                            | estRows | task      | access object        | operator info                                           |
+-------------------------------+---------+-----------+----------------------+---------------------------------------------------------+
| IndexLookUp_8                 | 0.01    | root      |                      |                                                         |
| ├─IndexRangeScan_5(Build)     | 10.00   | cop[tikv] | table:t1, index:c(c) | range:[3924541,3924541], keep order:false, stats:pseudo |
| └─Selection_7(Probe)          | 0.01    | cop[tikv] |                      | eq(test.t1.b, 2)                                        |
|   └─TableRowIDScan_6          | 10.00   | cop[tikv] | table:t1             | keep order:false, stats:pseudo                          |
+-------------------------------+---------+-----------+----------------------+---------------------------------------------------------+
4 rows in set (0.00 sec)

The query SELECT /*+ use_index(@sel_1 test.t1 c) */ * FROM test.t1 WHERE b=2 AND c=3924541 would be normalized as select * from test . t1 where b = ? and c = ?, while the original_sql of the created bind is select * from t1 where b = ? and c = ?, they do not match, so the bind cannot be hit.

eurekaka on Oct 21, 2020