br/lightning: support pd_enable_follower_handle_region

[okJiang]

What problem does this PR solve?

Issue Number: close #58651

Problem Summary:

After this pr, if tidb enables pd_enable_follower_handle_region, BR/ lightning will also benefit from this parameter and send ScanRegions/GetRegion to PD follower/leader distributively.

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.

if TiDB enables `pd_enable_follower_handle_region`, BR/ lightning will also benefit from it.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 75.2504%. Comparing base (068b9a8) to head (cfa4ce3).
Report is 18 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #58653        +/-   ##
================================================
+ Coverage   73.1093%   75.2504%   +2.1410%     
================================================
  Files          1676       1722        +46     
  Lines        463369     475543     +12174     
================================================
+ Hits         338766     357848     +19082     
+ Misses       103786      95424      -8362     
- Partials      20817      22271      +1454     

Flag	Coverage Δ
integration	49.1553% <25.0000%> (?)
unit	72.7672% <75.0000%> (+0.4663%)	⬆️

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

Components	Coverage Δ
dumpling	52.6910% <ø> (ø)
parser	∅ <ø> (∅)
br	61.3535% <50.0000%> (+15.5421%)	⬆️

[okJiang]

/retest

[okJiang]

/cc @3pointer @YuJuncen @lance6716 @D3Hunter

[lance6716]

can you provide some information about the behaviour? for example, will the follower returns the latest information like a TiDB follower read?

Please also add this description in the comment of WithAllowFollowerHandle

[okJiang]

can you provide some information about the behaviour? for example, will the follower returns the latest information like a TiDB follower read?

The followers exist a slight delay compared to the PD leader, and they synchronize region data through a syncer. Therefore, followers may not necessarily return the latest information. I have checked all the modified requests, and they should all have a retry mechanism, as the PD leader cannot guarantee that the region information is up to date.

Whatever, from the actual effect of enabling pd_enable_follower_handle_region in TiDB , this feature still offers significant benefits in scenarios with a massive number of regions. It can significantly reduce the load pressure on the PD leader during POC.

Please also add this description in the comment of WithAllowFollowerHandle

WithAllowFollowerHandle is a client switch. It takes effect in combination with pd_enable_follower_handle_region. This means that when this variable is not set, all requests are the same as before. When this variable is set, only requests that include WithAllowFollowerHandle may be sent to the follower. After discussion, I will add comment to it.

@lance6716

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lance6716, YuJuncen

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

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Needs approval from an approver in each of these files:

• OWNERS [YuJuncen,lance6716]
• br/OWNERS [YuJuncen]
• pkg/ddl/OWNERS [lance6716]
• pkg/lightning/OWNERS [lance6716]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-01-03 04:47:08.807323161 +0000 UTC m=+671364.163327700: ☑️ agreed by lance6716.
• 2025-01-03 07:26:02.576321337 +0000 UTC m=+680897.932325876: ☑️ agreed by YuJuncen.