sessionctx: add some information about the rewriting phase into the slow log

[qw4990]

What problem does this PR solve?

Issue Number: #17557

Problem Summary: add some information about the rewriting phase into the slow log

What is changed and how it works?

One step to resolve #17557.
Add three fields to slow logs:

1. Rewrite_time: the time cost to rewrite the query;
2. Preprocessed_subqueries: the number of pre-processed subqueries;
3. Preprocessed_subquery_time: the total time of pre-processing subqueries.

For example, in this query:

select * from t where a > (select min(a+sleep(1)) from t t2 where t2.a<5);

The subquery is not related with the outside query so it will be processed during the rewriting phase.
After this PR, you can see this information in its slow log:

# Rewrite_time: 3.00518165 Preproc_subqueries: 1 Preproc_subqueries_time: 3.004869107

Related changes

• PR to update pingcap/docs/pingcap/docs-cn: update the relative docs about the slow query.

Check List

Tests

• Unit test

Release note

• Add some information about the rewriting phase into the slow log

[codecov]

Codecov Report

Merging #17569 into master will decrease coverage by 0.0041%.
The diff coverage is n/a.

@@               Coverage Diff                @@
##             master     #17569        +/-   ##
================================================
- Coverage   79.5690%   79.5649%   -0.0042%     
================================================
  Files           524        524                
  Lines        142250     142182        -68     
================================================
- Hits         113187     113127        -60     
- Misses        19968      19987        +19     
+ Partials       9095       9068        -27     

[Reminiscent]

LGTM

[crazycs520]

LGTM,
Remember to update the docs.

[qw4990]

LGTM,
Remember to update the docs.

Ok, thx.

[sre-bot]

/run-all-tests

[sre-bot]

@qw4990 merge failed.

[qw4990]

/run-all-tests

[qw4990]

/run-all-tests

[breezewish]

#17557 need to be re-opened :)

[ti-srebot]

cherry pick to release-4.0 in PR #18164