Fix dangling TxnStatus pointer in LockResolver

[gengliqi]

fix #246
Return a copy of the cached TxnStatus to keep it valid after concurrent cache eviction.

Summary by CodeRabbit

• Refactor
  • Updated lock-resolution cache retrieval to use an “absence vs. present” return pattern, improving reliability when cached transaction information is missing.
  • Ensured cached statuses are returned consistently without relying on null pointer checks.
• Bug Fixes
  • Fixed transaction lock-status handling to better reflect resolved-state availability, reducing the risk of incorrect or stale status reads.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: fa729238-f543-480e-b85f-e38f51128c4d

📥 Commits

Reviewing files that changed from the base of the PR and between dc5fe53 and 662f740.

📒 Files selected for processing (2)

• include/pingcap/kv/LockResolver.h
• src/kv/LockResolver.cc

🚧 Files skipped from review as they are similar to previous changes (1)

• src/kv/LockResolver.cc

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📝 Walkthrough

Walkthrough

LockResolver now returns cached transaction statuses by value through std::optional, and getTxnStatus checks for an available cached value before returning it.

Changes

Lock status cache

Layer / File(s)	Summary
Optional cached status lookup include/pingcap/kv/LockResolver.h, src/kv/LockResolver.cc	getResolved returns std::nullopt or a copied TxnStatus, and getTxnStatus handles the optional result.

Estimated code review effort: 2 (Simple) | ~5 minutes

Suggested reviewers: windtalker

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title matches the main change: fixing a dangling TxnStatus pointer in LockResolver.
Linked Issues check	✅ Passed	The change returns a copy of the cached TxnStatus, which prevents a dangling pointer when the cache is evicted concurrently.
Out of Scope Changes check	✅ Passed	The PR stays focused on the LockResolver cache lookup and its call site, with no clear unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• OWNERS [ekexium,overvenus]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-07-21 10:15:29.938842417 +0000 UTC m=+1313515.974937474: ☑️ agreed by ekexium.
• 2026-07-21 10:46:43.689627016 +0000 UTC m=+1315389.725722072: ☑️ agreed by overvenus.

[gengliqi]

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