external: S3 concurrent reader releases memory after it's not used

[lance6716]

What problem does this PR solve?

Issue Number: ref #45719

Problem Summary:

What is changed and how it works?

When turn off concurrent reader, free the memory immediately.

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.

run TestMemoryUsageWhenHotspotChange
before

    iter_test.go:486: memory usage: 10518528 -> 7654735872

after

    iter_test.go:493: memory usage: 10706944 -> 944136192

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

[tiprow]

Hi @lance6716. Thanks for your PR.

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[codecov]

Codecov Report

Merging #47239 (145aabf) into master (cc42e4b) will increase coverage by 0.4309%.
The diff coverage is 85.5263%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #47239        +/-   ##
================================================
+ Coverage   72.2961%   72.7270%   +0.4309%     
================================================
  Files          1352       1373        +21     
  Lines        400865     407305      +6440     
================================================
+ Hits         289810     296221      +6411     
- Misses        91856      92302       +446     
+ Partials      19199      18782       -417     

Flag	Coverage Δ
integration	38.6783% <0.0000%> (?)
unit	72.2940% <85.5263%> (-0.0022%)	⬇️

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

Components	Coverage Δ
dumpling	53.9913% <ø> (ø)
parser	84.7544% <ø> (-0.0108%)	⬇️
br	48.8583% <85.5263%> (-4.2259%)	⬇️

[Benjamin2037]

Is this mean reader buffer size 4M?

[lance6716]

it's per concurrency of a reader, I'll rename it.

[lance6716]

e8773f5

[tangenta]

Rest LGTM

[tangenta]

/lgtm

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-09-27 09:04:19.691817257 +0000 UTC m=+6257.278927401: ☑️ agreed by tangenta.
• 2023-10-07 05:23:12.184306667 +0000 UTC m=+856989.771416811: ☑️ agreed by wjhuang2016.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Leavrth, tangenta, wjhuang2016

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[lance6716]

/retest

[tiprow]

@lance6716: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/retest

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