statsitics: clear the fmsketch's map correctly (#49379)

[ti-chi-bot]

This is an automated cherry-pick of #49379

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

[elsa0520]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• OWNERS [hawkingrei]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-12-13 04:19:55.625244045 +0000 UTC m=+416286.662470969: ☑️ agreed by hawkingrei.
• 2023-12-13 04:29:10.189452347 +0000 UTC m=+416841.226679274: ☑️ agreed by elsa0520.

[hawkingrei]

/retest

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-7.5@cf7a0af). Click here to learn what that means.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #49402   +/-   ##
================================================
  Coverage               ?   71.9692%           
================================================
  Files                  ?       1400           
  Lines                  ?     406486           
  Branches               ?          0           
================================================
  Hits                   ?     292545           
  Misses                 ?      94231           
  Partials               ?      19710           

Flag	Coverage Δ
unit	71.9692% <0.0000%> (?)

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

Components	Coverage Δ
dumpling	53.9913% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.2395% <0.0000%> (?)

[hawkingrei]

/retest