statistics: move MergePartTopN2GlobalTopN into handle/globalstats

[hawkingrei]

What problem does this PR solve?

Issue Number: ref #46905

Problem Summary:

What is changed and how it works?

We find it just use 100+ MB memory when to merge global topn without the largest number of partition. so for speeding up the merge-topn, we need to add more data structures such as bloomfilter. so we need to move the MergePartTopN2GlobalTopN into handle/globalstats.

just move the code. not change logical.

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

[codecov]

Codecov Report

Merging #47901 (e3c86ab) into master (515899f) will increase coverage by 1.1114%.
Report is 1 commits behind head on master.
The diff coverage is 77.7777%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #47901        +/-   ##
================================================
+ Coverage   71.7312%   72.8427%   +1.1114%     
================================================
  Files          1399       1422        +23     
  Lines        405473     411974      +6501     
================================================
+ Hits         290851     300093      +9242     
+ Misses        94905      93033      -1872     
+ Partials      19717      18848       -869     

Flag	Coverage Δ
integration	41.8404% <68.5185%> (?)
unit	71.7947% <77.7777%> (+0.0634%)	⬆️

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

Components	Coverage Δ
dumpling	53.9913% <ø> (ø)
parser	∅ <ø> (∅)
br	48.8839% <ø> (-4.0817%)	⬇️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qw4990, time-and-fate

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-10-23 02:40:03.414742151 +0000 UTC m=+2229601.001852297: ☑️ agreed by qw4990.
• 2023-10-23 03:29:47.97192902 +0000 UTC m=+2232585.559039164: ☑️ agreed by time-and-fate.

[hawkingrei]

/cherrypick release-7.5

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #47911.

[ti-chi-bot]

@hawkingrei: new pull request could not be created: failed to create pull request against pingcap/tidb#release-7.5 from head ti-chi-bot:cherry-pick-47901-to-release-7.5: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-47901-to-release-7.5."}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request"}

In response to this:

/cherrypick release-7.5

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