store/tikv: fix a memory leak in the batchClient for the large transactions

[tiancaiamao]

What problem does this PR solve?

Fix a memory leak.

What is changed and how it works?

Change xxx = xxx[:0] to some deep reset operation.

Check List

Tests

• Manual test (add detailed scripts or steps below)

Run some large transactions severals and observe the heap pprof.

mysql> truncate table sbtest2;                                                                                                                                                                        Query OK, 0 rows affected (1.15 sec)

mysql> insert into sbtest2 select * from sbtest1 limit 15000000;                                                                                                                                      Query OK, 15000000 rows affected (4 min 48.79 sec)
Records: 15000000  Duplicates: 0  Warnings: 0

mysql> truncate sbtest2;
Query OK, 0 rows affected (1.15 sec)

mysql> insert into sbtest2 select * from sbtest1 limit 10000000;
Query OK, 10000000 rows affected (2 min 59.24 sec)
Records: 10000000  Duplicates: 0  Warnings: 0

mysql> truncate sbtest2;
Query OK, 0 rows affected (1.04 sec)

mysql> insert into sbtest2 select * from sbtest1 limit 5000000;
Query OK, 5000000 rows affected (1 min 30.57 sec)
Records: 5000000  Duplicates: 0  Warnings: 0

Side effects

• Possible performance regression

Related changes

• Need to cherry-pick to the release branch

Release note

• Write release note for bug-fix or new feature.

[tiancaiamao]

[tiancaiamao]

pprof.tidb-server.alloc_objects.alloc_space.inuse_objects.inuse_space.841.pb.gz

[tiancaiamao]

PTAL @coocood @lysu

[lysu]

LGTM

[coocood]

LGTM

[coocood]

/merge

[sre-bot]

/run-all-tests

[sre-bot]

@tiancaiamao merge failed.

[coocood]

/run-integration-common-test

[codecov]

Codecov Report

Merging #14031 into master will decrease coverage by 0.4856%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##            master     #14031        +/-   ##
===============================================
- Coverage   80.638%   80.1523%   -0.4857%     
===============================================
  Files          482        482                
  Lines       123479     120780      -2699     
===============================================
- Hits         99571      96808      -2763     
- Misses       16187      16232        +45     
- Partials      7721       7740        +19

[sre-bot]

cherry pick to release-3.0 in PR #14032

[tiancaiamao]

Fix #13883