hard-invalidate region on RegionNotFound instead of async reload

[mittalrishabh]

issue #1892

The original fix does not work because in-flight requests continue to fail with region-not-found errors. This change hard-invalidates the region so that concurrent requests stop using the stale cache, and introduces a regionInvalidatedForRetry flag to allow the current request to retry on the leader before giving up.

Unit test

Deployed in prod to verify that it fixed region-not-found errors

Summary by CodeRabbit

• Bug Fixes
  • Improved region cache invalidation to be synchronous instead of asynchronous, ensuring more immediate consistency when region states change.
  • Enhanced retry logic to allow requests to attempt on the leader even after hard region invalidation, improving reliability in region-not-found scenarios.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR removes the AsyncInvalidateCachedRegion method from RegionCache and replaces asynchronous region invalidation with synchronous invalidation throughout the replica selector. A new regionInvalidatedForRetry flag enables leader retry attempts after hard invalidation, changing the invalidation behavior from async reload to sync invalidation with explicit retry control.

Changes

Cohort / File(s)	Summary
Region Cache Method Removal internal/locate/region_cache.go	Removed the public AsyncInvalidateCachedRegion method that previously enabled asynchronous reload on next access by setting sync flags.
Replica Selector Retry Logic internal/locate/replica_selector.go	Added regionInvalidatedForRetry field to track hard invalidation state and allow leader retry. Replaced AsyncInvalidateCachedRegion calls with synchronous InvalidateCachedRegion, enabling controlled retry behavior in next() and onRegionNotFound() paths.
Test Updates internal/locate/region_request_state_test.go, internal/locate/replica_selector_test.go	Updated test expectations to reflect hard invalidation instead of asynchronous reload; follower regions now transition to invalid state with comments clarifying the hard-invalidation-with-retry behavior.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• fast reload region on no-region-found error #1891: This PR directly reverses and modifies the async invalidation behavior introduced in PR #1891 by replacing AsyncInvalidateCachedRegion with synchronous invalidation and new retry logic.

Suggested labels

lgtm, approved

Suggested reviewers

• you06
• zyguan

Poem

🐰 Out with the async, in with the sync,
Region retries now quick in a blink,
Hard invalidation leads the way,
Leader retries save the day,
Simpler paths for cache to play!

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: replacing asynchronous region reload with hard invalidation when RegionNotFound occurs.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

📝 Coding Plan

• Generate coding plan for human review comments

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[rpaik]

@you06 and @zyguan could you help with the review? 🙏

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: you06, zyguan

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Needs approval from an approver in each of these files:

• OWNERS [you06,zyguan]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-03-18 07:46:35.954736172 +0000 UTC m=+343123.042393699: ☑️ agreed by zyguan.
• 2026-03-18 13:50:26.908380601 +0000 UTC m=+364953.996038128: ☑️ agreed by you06.