[ISSUE #10521] Use madvise(MADV_RANDOM) to disable kernel read-ahead during correctMinOffset binary search

[lizhimins]

What is the purpose of the change

close #10521

ConsumeQueue.correctMinOffset performs binary search on mmap files (random access pattern). The Linux kernel default read_ahead_kb on NVMe devices is aggressively large, so each page fault during binary search pulls in far more data than actually needed, producing periodic disk read pulses.

On cloud disks where read/write bandwidth share a single quota, these read pulses squeeze CommitLog writes and cause periodic send-RT spikes.

Brief changelog

• Call madvise(MADV_RANDOM) before binary search to disable read-ahead, restore madvise(MADV_NORMAL) in the finally block
• Add config switch correctMinOffsetMadviseEnable (default: off)
• Skip on Windows where madvise is not available
• Platform check cached as static final to avoid repeated evaluation

Verifying this change

• Added unit tests covering large dataset (5000 entries), small dataset (10 entries), and empty queue scenarios
• Production validation: send p99 stabilized at ~4ms with zero pulses over 60 minutes (previously 7 pulses/hour with p99 spikes to 26ms)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.08%. Comparing base (226e24f) to head (ac66627).
⚠️ Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
...n/java/org/apache/rocketmq/store/ConsumeQueue.java	35.71%	4 Missing and 5 partials ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #10523      +/-   ##
=============================================
- Coverage      48.18%   48.08%   -0.10%     
+ Complexity     13394    13369      -25     
=============================================
  Files           1377     1377              
  Lines         100730   100753      +23     
  Branches       13012    13019       +7     
=============================================
- Hits           48536    48449      -87     
- Misses         46264    46345      +81     
- Partials        5930     5959      +29     

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[RockteMQ-AI]

Review by github-manager-bot

Summary

Uses madvise(MADV_RANDOM) to disable kernel read-ahead during ConsumeQueue.correctMinOffset binary search on mmap'd files, addressing periodic disk read pulses that squeeze CommitLog writes on cloud disks.

Findings

• [Info] ConsumeQueue.java:619–640 — The madvise(MADV_RANDOM) setup is placed before the try block, and the restore (MADV_NORMAL) is in the finally block. This is correct: if the setup itself throws, MADV_RANDOM was never applied so there is nothing to restore. No gap between successful madvise and entering try.

• [Info] ConsumeQueue.java:46 — IS_LINUX = !MixAll.isWindows() is cached as static final — good, avoids repeated platform evaluation on every correctMinOffset call.

• [Info] MessageStoreConfig.java — New correctMinOffsetMadviseEnable defaults to false. Safe rollout path; operators opt in explicitly.

• [Info] ConsumeQueueTest.java — Three test scenarios (5000 entries, 10 entries, empty queue) with sequential correction calls verify that MADV_NORMAL is properly restored between invocations. Good coverage.

• [Info] LibC.java — MADV_RANDOM = 1 and madvise(Pointer, NativeLong, int) already exist in the codebase; no new native bindings needed.

Suggestions

• Minor: Consider adding a log.debug when madvise(MADV_RANDOM) is successfully applied (not just on failure), to aid production diagnostics when the feature is enabled. Optional.

Verdict

Well-scoped optimization with production validation data (p99 stabilized at ~4ms, zero pulses vs 7/hour before). Config-gated, properly guarded, and well-tested. LGTM.

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Automated review by github-manager-bot

[lollipopjin]

LGTM