ingest: skip write when the region has no leader (#64442)

[ti-chi-bot]

This is an automated cherry-pick of #64442

What problem does this PR solve?

Issue Number: close #64422, ref #61702

Problem Summary:

What changed and how does it work?

this issue only happens in nextgen, as classic region job worker already have an additional leader check after write to tikv, we fix this by check region leader before write, so for classic kernel we can avoid the useless write

tidb/pkg/lightning/backend/local/region_job.go

Line 632 in 87152f7

if len(leaderPeerMetas) == 0 {

also log the unretryable error, to help debug and direct us to add more retryable error

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

we run the same scenario in the issue, no such error again, and we can see errors like below when there is no leader for some scanned region

[2025/11/13 15:46:11.734 +08:00] [INFO] [local.go:1497] ["put job back to jobCh to retry later"] [keyspaceName=SYSTEM] [task-id=120016] [task-key=keyspace_a/ImportInto/120016] [subtaskID=270022] [step=ingest] [startKey=780000017480000000000000C55F7280000000003C8F88] [endKey=780000017480000000000000C55F7280000000003C9901] [stage=regionScanned] [retryCount=1] [waitUntil=2025/11/13 15:46:13.734 +08:00] [error="[KV:ErrNoLeader]region has no leader, region '326782'"]

• 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

[codecov]

Codecov Report

❌ Patch coverage is 78.26087% with 5 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release-nextgen-20251011@146db01). Learn more about missing BASE report.

Additional details and impacted files

@@                      Coverage Diff                      @@
##             release-nextgen-20251011     #64470   +/-   ##
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Flag	Coverage Δ
unit	72.0863% <78.2608%> (?)

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Components	Coverage Δ
dumpling	52.8700% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	46.4097% <0.0000%> (?)

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[Benjamin2037]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Benjamin2037, D3Hunter

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Details

Needs approval from an approver in each of these files:

• OWNERS [Benjamin2037,D3Hunter]
• pkg/ingestor/OWNERS [Benjamin2037,D3Hunter]
• pkg/lightning/OWNERS [Benjamin2037,D3Hunter]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-11-13 11:57:31.804979265 +0000 UTC m=+962501.248009144: ☑️ agreed by D3Hunter.
• 2025-11-14 01:58:32.734111984 +0000 UTC m=+1012962.177141863: ☑️ agreed by Benjamin2037.