statsitics: clear the fmsketch's map correctly

[hawkingrei]

What problem does this PR solve?

Issue Number: close #49381

Problem Summary:

What changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

before

after:

The new one has better CPU usage.

the left one is the old, the right one is the new.

• 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

[codecov]

Codecov Report

Merging #49379 (7d902ad) into master (49f89a9) will increase coverage by 0.7929%.
Report is 6 commits behind head on master.
The diff coverage is 100.0000%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #49379        +/-   ##
================================================
+ Coverage   71.0490%   71.8420%   +0.7929%     
================================================
  Files          1368       1412        +44     
  Lines        401711     415620     +13909     
================================================
+ Hits         285412     298590     +13178     
- Misses        96443      98198      +1755     
+ Partials      19856      18832      -1024     

Flag	Coverage Δ
integration	43.8429% <100.0000%> (?)
unit	71.0483% <ø> (-0.0008%)	⬇️

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

Components	Coverage Δ
dumpling	53.9663% <ø> (ø)
parser	∅ <ø> (∅)
br	47.9211% <ø> (-4.9723%)	⬇️

[elsa0520]

LGTM

[elsa0520]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: elsa0520, winoros

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• OWNERS [elsa0520,winoros]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-12-12 10:38:29.550826199 +0000 UTC m=+352600.588053126: ☑️ agreed by elsa0520.
• 2023-12-12 10:44:45.121335909 +0000 UTC m=+352976.158562854: ☑️ agreed by winoros.

[hawkingrei]

/retest

[hawkingrei]

/cherrypick release-7.5

[ti-chi-bot]

@hawkingrei: new pull request created to branch release-7.5: #49402.

In response to this:

/cherrypick release-7.5

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