Fix sequence number race when allowing writes during external SST ingestion (#435)

[ti-chi-bot]

This is an automated cherry-pick of #435

Ref tikv/tikv#19891 (comment)

When allow_write=true, external SST ingestion may assign sequence numbers
concurrently with foreground writes. This can cause duplicate sequence numbers
or make the global sequence-number state move backwards.

This change briefly blocks writers to reserve enough sequence numbers before
running the ingestion jobs. Writers are resumed immediately after the
reservation, so SST processing and MANIFEST updates remain outside the
write-blocking period.

The existing behavior for allow_write=false is unchanged.

This also fixes an enable_multi_batch_write edge case where writers that fail
to write WAL still publish their allocated sequence numbers but were not counted
as pending. They are now included in pending-write accounting, preventing
ingestion from reserving sequence numbers before their sequence publication
completes.

Summary by CodeRabbit

• Bug Fixes

  • Improved external SST file ingestion while writes occur concurrently.
  • Ensured ingestion waits for pending writes before applying imported data.
  • Preserved consistent sequence numbering and prevented conflicts with new writes.
  • Maintained snapshot isolation so earlier snapshots do not expose newly ingested files.

• Documentation

  • Clarified concurrent-write requirements and snapshot behavior for external file ingestion.

• Tests

  • Added coverage for concurrent writes and multi-file ingestion.
  • Verified write ordering, final values, sequence assignments, and snapshot visibility.

[ti-chi-bot]

@gengliqi This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[coderabbitai]

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[Copilot]

Pull request overview

Fixes sequence-number races between foreground writes and external SST ingestion.

Changes:

• Reserves ingestion sequence numbers while writers are briefly blocked.
• Extends pending-write accounting to failed multi-batch writes.
• Adds concurrency, ordering, and snapshot tests plus API documentation.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
include/rocksdb/options.h	Documents concurrent ingestion constraints.
db/external_sst_file_test.cc	Adds concurrency regression tests.
db/external_sst_file_ingestion_job.h	Passes sequence baseline into ingestion jobs.
db/external_sst_file_ingestion_job.cc	Uses the reserved sequence baseline.
db/db_impl/db_impl.h	Clarifies pending-write accounting.
db/db_impl/db_impl.cc	Blocks writers and reserves ingestion sequences.
db/db_impl/db_impl_write.cc	Accounts for failed multi-batch writes.

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gengliqi, overvenus

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Details

Needs approval from an approver in each of these files:

• OWNERS [gengliqi,overvenus]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-08-11 11:35:27.906744376 +0000 UTC m=+3132713.942839432: ☑️ agreed by gengliqi.
• 2026-08-12 06:12:33.760937406 +0000 UTC m=+3199739.797032462: ☑️ agreed by overvenus.