planner: use a deep copy for accessPath when clone DataSource

[francis0407]

What problem does this PR solve?

Before this PR:

mysql> create table t(a int, b int)partition by range columns(a)(partition p0 values less than (10), partition p1 values less than(20), partition p2 values less than(30));
Query OK, 0 rows affected (0.01 sec)

mysql> insert into t values (21, 1), (22, 2), (23, 3), (24, 4), (15, 5);
Query OK, 5 rows affected (0.01 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql> analyze table t;
Query OK, 0 rows affected (0.01 sec)

mysql> explain select * from t;
+------------------------+----------+-----------+--------------------------------------------------------------------------+
| id                     | count    | task      | operator info                                                            |
+------------------------+----------+-----------+--------------------------------------------------------------------------+
| Union_8                | 10005.00 | root      |                                                                          |
| ├─TableReader_10       | 4.00     | root      | data:TableScan_9                                                         |
| │ └─TableScan_9        | 4.00     | cop[tikv] | table:t, partition:p0, range:[-inf,+inf], keep order:false, stats:pseudo |
| ├─TableReader_12       | 1.00     | root      | data:TableScan_11                                                        |
| │ └─TableScan_11       | 1.00     | cop[tikv] | table:t, partition:p1, range:[-inf,+inf], keep order:false               |
| └─TableReader_14       | 4.00     | root      | data:TableScan_13                                                        |
|   └─TableScan_13       | 4.00     | cop[tikv] | table:t, partition:p2, range:[-inf,+inf], keep order:false               |
+------------------------+----------+-----------+--------------------------------------------------------------------------+
7 rows in set (0.00 sec)

After this PR:

        "SQL": "explain select * from t",
        "Result": [
          "Union_8 10005.00 root ",
          "├─TableReader_10 10000.00 root data:TableScan_9",
          "│ └─TableScan_9 10000.00 cop[tikv] table:t, partition:p0, range:[-inf,+inf], keep order:false, stats:pseudo",
          "├─TableReader_12 1.00 root data:TableScan_11",
          "│ └─TableScan_11 1.00 cop[tikv] table:t, partition:p1, range:[-inf,+inf], keep order:false",
          "└─TableReader_14 4.00 root data:TableScan_13",
          "  └─TableScan_13 4.00 cop[tikv] table:t, partition:p2, range:[-inf,+inf], keep order:false"
        ]

What is changed and how it works?

When processing partition tables, we use a shallow copy for DataSouces. But accessPaths in DataSouces will be changed after that. So we need a deep copy here.

Check List

Tests

• Unit test

Related changes

• Need to cherry-pick to the release branch

Release note

• Fix partition table use wrong stats info in physical optimization.

[francis0407]

/run-all-tests

[winoros]

lgtm

[francis0407]

/rebuild

[codecov]

Codecov Report

Merging #13620 into master will increase coverage by 0.0404%.
The diff coverage is n/a.

@@               Coverage Diff                @@
##             master     #13620        +/-   ##
================================================
+ Coverage   79.9522%   79.9927%   +0.0404%     
================================================
  Files           473        473                
  Lines        115724     115988       +264     
================================================
+ Hits          92524      92782       +258     
+ Misses        15944      15942         -2     
- Partials       7256       7264         +8

[eurekaka]

LGTM

[sre-bot]

Your auto merge job has been accepted, waiting for 13621, 13470

[sre-bot]

/run-all-tests

[francis0407]

/run-cherry-picker

[sre-bot]

cherry pick to release-2.1 in PR #13627

[sre-bot]

cherry pick to release-3.0 in PR #13628