br: enhance version info logging, trim keyspace prefix for region merging

[YuJuncen]

What problem does this PR solve?

Issue Number: close #64195

Problem Summary:
br --version doesn't contain the kenrnel type though we are building Next Gen BR in our pipeline. This can be confusing and error-prone.

Also this PR trims keyspace prefix when merging small files.

What changed and how does it work?

Added Kernel Type to BR version.

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

[tiprow]

Hi @YuJuncen. Thanks for your PR.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.7770%. Comparing base (bb0b895) to head (83677b1).
⚠️ Report is 23 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #64178        +/-   ##
================================================
+ Coverage   72.6850%   74.7770%   +2.0920%     
================================================
  Files          1858       1859         +1     
  Lines        502321     505643      +3322     
================================================
+ Hits         365112     378105     +12993     
+ Misses       114988     104605     -10383     
- Partials      22221      22933       +712     

Flag	Coverage Δ
integration	45.7124% <84.2105%> (?)
unit	72.5312% <100.0000%> (+0.2829%)	⬆️

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

Components	Coverage Δ
dumpling	52.8700% <ø> (ø)
parser	∅ <ø> (∅)
br	63.2948% <100.0000%> (+16.9323%)	⬆️

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[3pointer]

Do we need to check kernel type has a conflict with config --keyspace-name before backup and restore?

[YuJuncen]

TiKV itself supports ApiV2. I think it is reasonable to restore to a keyspace with TiKV.

[3pointer]

We use this flag to determine restore logic (e.g. download one peer/three peers)
is that ok using next-gen type br to restore ApiV2 classical tikv?

[YuJuncen]

I think we'd better use kerneltype.IsNextGen to determine whether download to all peers.

[YuJuncen]

/test pull-br-integration-test

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/test pull-br-integration-test

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: 3pointer

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-10-31 07:32:37.63953479 +0000 UTC m=+1634663.716787349: ☑️ agreed by 3pointer.