*: add a blacklist to disallow pushing down specific expressions

[XuHuaiyu]

What problem does this PR solve?

This commit adds a switch to support manually control wether to push down expressions.

What is changed and how it works?

1. Add a system table mysql.expr_pushdown_blacklist

tidb> show create table mysql.expr_pushdown_blacklist;
+-------------------------+----------------------------------------------------------------------------------------------------------------------------------+
| Table                   | Create Table                                                                                                                     |
+-------------------------+----------------------------------------------------------------------------------------------------------------------------------+
| expr_pushdown_blacklist | CREATE TABLE `expr_pushdown_blacklist` (
  `name` char(100) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-------------------------+----------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

tidb> create table t(a int);
Query OK, 0 rows affected (0.00 sec)

tidb> desc select * from t where a < 1;
+---------------------+----------+------+------------------------------------------------------------+
| id                  | count    | task | operator info                                              |
+---------------------+----------+------+------------------------------------------------------------+
| TableReader_7       | 3323.33  | root | data:Selection_6                                           |
| └─Selection_6       | 3323.33  | cop  | lt(test.t.a, 1)                                            |
|   └─TableScan_5     | 10000.00 | cop  | table:t, range:[-inf,+inf], keep order:false, stats:pseudo |
+---------------------+----------+------+------------------------------------------------------------+
3 rows in set (0.00 sec)

tidb> insert into mysql.expr_pushdown_blacklist values("lt");
Query OK, 1 row affected (0.00 sec)

tidb> desc select * from t where a < 1;
+---------------------+----------+------+------------------------------------------------------------+
| id                  | count    | task | operator info                                              |
+---------------------+----------+------+------------------------------------------------------------+
| TableReader_7       | 3323.33  | root | data:Selection_6                                           |
| └─Selection_6       | 3323.33  | cop  | lt(test.t.a, 1)                                            |
|   └─TableScan_5     | 10000.00 | cop  | table:t, range:[-inf,+inf], keep order:false, stats:pseudo |
+---------------------+----------+------+------------------------------------------------------------+
3 rows in set (0.00 sec)

tidb> admin reload expr_pushdown_blacklist;                                         Query OK, 0 rows affected (0.00 sec)

tidb> desc select * from t where a < 1;
+---------------------+----------+------+------------------------------------------------------------+
| id                  | count    | task | operator info                                              |
+---------------------+----------+------+------------------------------------------------------------+
| Selection_5         | 8000.00  | root | lt(test.t.a, 1)                                            |
| └─TableReader_7     | 10000.00 | root | data:TableScan_6                                           |
|   └─TableScan_6     | 10000.00 | cop  | table:t, range:[-inf,+inf], keep order:false, stats:pseudo |
+---------------------+----------+------+------------------------------------------------------------+
3 rows in set (0.00 sec)

Check List

Tests

• Integration test
• Manual test
  As the above mentioned.

Code changes

• Has exported function/method change
• Has exported variable/fields change

Side effects

N/A

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

[codecov]

Codecov Report

Merging #10688 into master will decrease coverage by 0.1443%.
The diff coverage is 87.5%.

@@               Coverage Diff                @@
##             master     #10688        +/-   ##
================================================
- Coverage   80.3172%   80.1728%   -0.1444%     
================================================
  Files           415        416         +1     
  Lines         88260      88389       +129     
================================================
- Hits          70888      70864        -24     
- Misses        12181      12285       +104     
- Partials       5191       5240        +49

[XuHuaiyu]

related PR: pingcap/parser#350

[alivxxx]

Can we merge this function with Next()？ Seems that they are the same.

[alivxxx]

LGTM

[qw4990]

LGTM

[qw4990]

/run-all-tests