stats: avoid creating pseudo stats table when dumping stats delta (#62887)

[ti-chi-bot]

This is an automated cherry-pick of #62887

What problem does this PR solve?

Issue Number: close #62590

Problem Summary:

based on issue reproduction and memory analysis , the majority of memory waste comes from creating pseudo stats table when doing needDumpStatsDelta check, we can simply use a lightweight approach to solve it without changing too much of the code.

This is happening during millions table workload while dumping stats happens frequently, in the issue mentioned smaller table size should also have same effect but I was unable to reproduce, maybe query creates only limited number of pseudo stats and quickly got GC, whereas dump stats happened for all tables in a burst, causing memory pressure.

What changed and how does it work?

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

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

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[0xPoe]

Thanks!

[0xPoe]

This would help reduce this CPU burn:

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (release-8.5@69b1dbe). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #64565   +/-   ##
================================================
  Coverage               ?   76.4701%           
================================================
  Files                  ?       1654           
  Lines                  ?     456109           
  Branches               ?          0           
================================================
  Hits                   ?     348787           
  Misses                 ?      86214           
  Partials               ?      21108           

Flag	Coverage Δ
integration	48.9974% <100.0000%> (?)
unit	72.7296% <100.0000%> (?)

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

Components	Coverage Δ
dumpling	52.9278% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	52.6842% <0.0000%> (?)

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: 0xPoe, time-and-fate

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• pkg/statistics/OWNERS [0xPoe,time-and-fate]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-11-19 10:02:41.259986749 +0000 UTC m=+92324.909181196: ☑️ agreed by 0xPoe.
• 2025-11-19 10:33:36.615204997 +0000 UTC m=+94180.264399444: ☑️ agreed by time-and-fate.