variable: add variable to control the concurrency of buildSampling

[hawkingrei]

…idb_build_stats_concurrency as 2

What problem does this PR solve?

Issue Number: close #47583

Problem Summary:

What is changed and how it works?

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

[easonn7]

/approve

[codecov]

Codecov Report

Merging #47582 (2ff7615) into master (da1f487) will increase coverage by 0.9809%.
Report is 14 commits behind head on master.
The diff coverage is 100.0000%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #47582        +/-   ##
================================================
+ Coverage   71.8924%   72.8733%   +0.9809%     
================================================
  Files          1353       1375        +22     
  Lines        401070     408311      +7241     
================================================
+ Hits         288339     297550      +9211     
+ Misses        93320      91986      -1334     
+ Partials      19411      18775       -636     

Flag	Coverage Δ
integration	40.8095% <100.0000%> (?)
unit	72.0320% <100.0000%> (+0.1395%)	⬆️

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

Components	Coverage Δ
dumpling	53.9913% <ø> (ø)
parser	84.7328% <ø> (+0.0107%)	⬆️
br	49.0089% <ø> (-4.3512%)	⬇️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: easonn7, qw4990, winoros

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [qw4990,winoros]
• sessionctx/variable/OWNERS [easonn7]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-10-12 14:18:08.518960716 +0000 UTC m=+1321086.106070864: ☑️ agreed by winoros.
• 2023-10-13 02:36:49.586498393 +0000 UTC m=+1365407.173608537: ☑️ agreed by qw4990.

[hawkingrei]

/retest