infoschema/slow_query: fix shallow copy problem

[crazycs520]

What problem does this PR solve?

tidb-slow.log
parse upper slow log and execute below:

root:information_schema> select user, db,digest from slow_query where user != "";
+----------+--------------------+------------------------------------------------------------------+
| user     | db                 | digest                                                           |
+----------+--------------------+------------------------------------------------------------------+
| riv,Crea |                    | ow_db_priv,Super_priv,Execute_priv,Create_view_priv,Show_view_pr |
| nternal: | 0381ff1b5c2994d657 | s_priv:pseudo                                                    |
|          |                    | # Num_cop_tasks: 1                                               |
|          |                    | # Cop_proc_avg: 0 Cop_proc_p90:                                  |
| lumns_pr |  Txn_start_ts: 408 | 00136655                                                         |
|          |                    | # Wait_time: 0.001 Request_count: 1 Total_keys: 1                |
|          |                    | # Is_                                                            |
+----------+--------------------+------------------------------------------------------------------+
3 rows in set

There are some wrong value in user, db.

after fix:

root:information_schema> select user, db,digest from slow_query where user != "";
+----------+--------------------+------------------------------------------------------------------+
| user     | db                 | digest                                                           |
+----------+--------------------+------------------------------------------------------------------+
| root@::1 |                    | f106b0f6c630f454d31b008fbb034fda10f2441fd0477a9990e22b7df313f59a |
| root@::1 | information_schema | b4dae6a771c1d84157dcc302bef38cbff77a7a8ff89ee38302ac3324485454a3 |
| root@::1 | information_schema | b4dae6a771c1d84157dcc302bef38cbff77a7a8ff89ee38302ac3324485454a3 |
+----------+--------------------+------------------------------------------------------------------+
3 rows in set

What is changed and how it works?

Fix this by add copy.

Check List

Tests

• I can't reproduce this in a simple unit test ...

[codecov]

Codecov Report

Merging #10696 into master will increase coverage by 0.0069%.
The diff coverage is 100%.

@@               Coverage Diff                @@
##             master     #10696        +/-   ##
================================================
+ Coverage   78.3279%   78.3348%   +0.0069%     
================================================
  Files           414        414                
  Lines         87666      87717        +51     
================================================
+ Hits          68667      68713        +46     
- Misses        13854      13857         +3     
- Partials       5145       5147         +2

[codecov]

Codecov Report

Merging #10696 into master will decrease coverage by 0.0089%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##             master     #10696       +/-   ##
===============================================
- Coverage   79.6453%   79.6364%   -0.009%     
===============================================
  Files           414        414               
  Lines         87690      87681        -9     
===============================================
- Hits          69841      69826       -15     
- Misses        12677      12685        +8     
+ Partials       5172       5170        -2

[zz-jason]

LGTM

[coocood]

LGTM

[crazycs520]

/run-all-tests

[crazycs520]

/run-all-tests

[winkyao]

LGTM

[crazycs520]

/run-all-tests

[crazycs520]

/run-all-tests