Revert "planner: remove the useless variable tidb_enable_point_get_cache"

[jackysp]

What problem does this PR solve?

Issue Number: close #51007, also will close #48958

Problem Summary:

What changed and how does it work?

Revert #36844
Add tidb_enable_point_get_cache back.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[Defined2014]

Please close #48958 after this PR merged.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.4517%. Comparing base (f0a26dd) to head (a30a9e3).
Report is 1554 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #51008        +/-   ##
================================================
+ Coverage   70.5842%   72.4517%   +1.8675%     
================================================
  Files          1467       1567       +100     
  Lines        434825     477381     +42556     
================================================
+ Hits         306918     345871     +38953     
- Misses       108672     109335       +663     
- Partials      19235      22175      +2940     

Flag	Coverage Δ
integration	52.2081% <100.0000%> (?)
unit	70.3083% <100.0000%> (-0.0888%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	54.2940% <ø> (ø)
parser	∅ <ø> (∅)
br	56.7501% <ø> (+11.0049%)	⬆️

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-02-06 09:12:43.493383016 +0000 UTC m=+261689.060152915: ☑️ agreed by Defined2014.
• 2024-02-06 09:35:34.732666471 +0000 UTC m=+263060.299436361: ☑️ agreed by qw4990.

[Defined2014]

/cc @easonn7 @yudongusa

PTAL

[ti-chi-bot]

@Defined2014: GitHub didn't allow me to request PR reviews from the following users: yudongusa, easonn7.

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In response to this:

/cc @easonn7 @yudongusa

PTAL

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[AilinKid]

/retest

[yudongusa]

@jackysp did we have enough tests on adding this back to make sure it still works?

[jackysp]

@jackysp did we have enough tests on adding this back to make sure it still works?

@yudongusa When this switch was added originally, it seems that no testing was done. I think we can add the test for this switch in other pull requests. Currently, it is in a hidden state without documentation, so it will not affect customers either.

[qw4990]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: AilinKid, Defined2014, qw4990
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[tiprow]

@jackysp: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
tiprow_fast_test	a30a9e3	link	true	/test fast_test_tiprow
fast_test_tiprow	a30a9e3	link	true	/test fast_test_tiprow

Full PR test history. Your PR dashboard.

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[ti-chi-bot]

@jackysp: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/unit-test	a30a9e3	link	true	/test unit-test

Full PR test history. Your PR dashboard.

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[ti-chi-bot]

PR needs rebase.

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