[ISSUE #10462] Add memory backpressure to dispatch

[lizhimins]

What is the purpose of the change

Part of #10462

Add memory backpressure mechanism to the tiered storage dispatcher. When available heap memory falls below the configured threshold, dispatch is skipped to prevent OOM.

Brief changelog

• Add tieredStoreDispatchMinFreeMemoryRatio (default 0.1) and tieredStoreDispatchMinFreeMemoryMaxBytes (default 1GB) config
• Add isMemoryEnough() check before dispatch
• Remove Dispatcher semaphore, rely on thread pool natural throttling
• Rename dispatchWithSemaphore to dispatch

Verifying this change

• mvn compile succeeds
• mvn test -pl tieredstore passes (112 tests, 0 failures)

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 69.56522% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.99%. Comparing base (a6fb9e2) to head (c2fb6d1).
⚠️ Report is 10 commits behind head on develop.

Files with missing lines	Patch %	Lines
...q/tieredstore/core/MessageStoreDispatcherImpl.java	53.33%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #10470      +/-   ##
=============================================
- Coverage      48.03%   47.99%   -0.05%     
- Complexity     13286    13295       +9     
=============================================
  Files           1376     1377       +1     
  Lines         100558   100645      +87     
  Branches       12985    12996      +11     
=============================================
- Hits           48305    48302       -3     
- Misses         46333    46397      +64     
- Partials        5920     5946      +26     

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[oss-sentinel-ai]

Review: Approved ✅

PR: #10470 — Add memory backpressure to dispatch
Type: Enhancement (3 files, +51/-15)

Assessment

Adds memory backpressure mechanism to prevent OOM:

• Configurable min free memory ratio (default 0.1)
• Max bytes cap (default 1GB)
• isMemoryEnough() check before dispatch
• Removes Dispatcher semaphore, relies on thread pool throttling

Verdict

✅ Critical stability improvement for tiered storage. Part of #10462.

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🤖 Automated review by oss-sentinel-ai