fix standby crash on mem full

[liunyl]

Here are some reminders before you submit the pull request

• Add tests for the change
• Document changes
• Reference the link of issue using fixes eloqdb/tx_service#issue_id
• Reference the link of RFC if exists
• Pass ./mtr --suite=mono_main,mono_multi,mono_basic

Summary by CodeRabbit

• Bug Fixes
  • Improved system stability and resilience during memory constraints. Request processing is now intelligently deferred and queued when system resources reach maximum capacity, preventing out-of-memory failures that previously caused unexpected service disruptions. This enhancement particularly improves overall system reliability and stability on resource-constrained nodes and deployment environments.

[coderabbitai]

Walkthrough

Modified include/cc/object_cc_map.h to add a nullptr check for looked-up CCE. When not found, requests are enqueued to the memory-full wait list and the function returns false instead of proceeding. This guard applies to both initial request processing and standby-forward paths, preventing OOM scenarios on standby nodes.

Changes

Cohort / File(s)	Summary
Null pointer guard for CCE lookup include/cc/object_cc_map.h	Added nullptr check when CCE is not found during request lookup; enqueues request to memory-full wait list and returns false; prevents OOM on standby nodes; applied to both initial "first time processed" path and standby-forward path

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

• Verify the nullptr check is applied consistently in both code paths (initial and standby-forward)
• Confirm the memory-full wait list enqueueing behavior is the correct fallback mechanism
• Ensure the return value (false) is handled appropriately by callers

Suggested reviewers

• MrGuin

Poem

🐰 A nullptr guard, so neat and small,
Protects from crashes, saves us all—
When memory's tight and checks run deep,
The standby nodes can safely sleep!
hops with glee ✨

Pre-merge checks and finishing touches

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description only contains the template checklist with all items unchecked, but provides no actual implementation details, testing evidence, or issue references required for a complete PR description.	Add implementation details explaining the fix, confirm tests were added/passed, document changes, reference the issue with 'fixes eloqdb/tx_service#issue_id', and verify test suite passed.
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'fix standby crash on mem full' directly relates to the core change: fixing a standby crash when memory is full by adding a nullptr guard to prevent OOM scenarios.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch standby_oom

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

include/cc/object_cc_map.h (1)

1840-1840: Optional: Consider removing the now-redundant assertion.

After the nullptr check at lines 1835-1839, cce is guaranteed to be non-null at this point, making the assertion always true (dead code). While it doesn't cause any harm, you might consider removing it for clarity.

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between f4a1afb and 1984407.

📒 Files selected for processing (1)

• include/cc/object_cc_map.h (1 hunks)

🔇 Additional comments (1)

include/cc/object_cc_map.h (1)

1835-1839: LGTM! Fix prevents standby crash on OOM.

The nullptr check correctly handles the case where FindEmplace fails to allocate a new CCE due to memory exhaustion. By enqueuing the request to the memory-full wait list and returning false, the request will be retried once capacity becomes available. This pattern is consistent with other handlers in this file (e.g., ApplyCc at lines 430-456, ReplayLogCc at lines 2196-2205).