fix: cleanup legacy narinfo in PutNarInfo to avoid race condition

[kalbasit]

In a thundering herd scenario where multiple concurrent GetNarInfo and PutNarInfo calls occur for the same hash, PutNarInfo might commit to the database before GetNarInfo triggers a migration. This skips the migration logic, leaving legacy narinfo files in storage, which causes tests to fail and leads to storage inconsistency.

This change adds an explicit check for legacy narinfo files in PutNarInfo. If a file exists in the storage backend after the database update, it is now deleted. This ensures consistency regardless of which operation finishes first.

I have also added a deterministic test that uses hooks to force this race condition and verify that the cleanup always occurs.

[gemini-code-assist]

Summary of Changes

Hello @kalbasit, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical race condition that could lead to storage inconsistencies. By proactively cleaning up legacy narinfo files during the PutNarInfo operation, it guarantees that the storage state remains consistent, regardless of the timing of concurrent operations, thereby preventing test failures and maintaining data integrity.

Highlights

• Race Condition Fix: Addresses a race condition in PutNarInfo where legacy narinfo files could persist in storage if PutNarInfo completed before a background migration, leading to storage inconsistency and test failures.
• Explicit Legacy Narinfo Cleanup: Introduces an explicit check and deletion mechanism within PutNarInfo to remove legacy narinfo files from the storage backend after the database update, ensuring consistency regardless of the timing of concurrent operations.

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[kalbasit]

• fix: cleanup legacy narinfo in PutNarInfo to avoid race condition #658 👈 (View in Graphite)
• main

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[gemini-code-assist]

Code Review

The pull request addresses a race condition in PutNarInfo that could lead to storage inconsistency. It adds an explicit check for legacy narinfo files in storage and deletes them after the database update. This ensures consistency regardless of the order in which GetNarInfo and PutNarInfo calls complete. The change appears to be well-reasoned and effectively mitigates the identified issue.

[kalbasit]

/gemini review

[gemini-code-assist]

Code Review

This pull request effectively addresses a race condition between GetNarInfo and PutNarInfo by ensuring legacy narinfo files are cleaned up from storage. The fix in PutNarInfo is straightforward and correctly placed. The addition of a deterministic test (TestGetNarInfo_RaceWithPutNarInfoDeterministic) is excellent, as it reliably reproduces the race condition using a clever hook, providing strong confidence in the fix. I have one suggestion to make the logging less noisy in certain race scenarios, but overall this is a high-quality contribution.

[kalbasit]

/gemini review

[gemini-code-assist]

Code Review

This pull request effectively addresses a race condition between GetNarInfo and PutNarInfo by ensuring PutNarInfo cleans up legacy narinfo files from storage. The fix is clean, well-commented, and directly solves the described problem. The addition of a deterministic test (TestGetNarInfo_RaceWithPutNarInfoDeterministic) is excellent; it's thorough and correctly simulates the complex race condition to verify the fix. I have one suggestion to make the new test slightly more robust against future changes.