Engine/MemoryCache: Stage 1 improvements (RFC #2647) #2649
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- Add non-reentrant Cleanup() (SemaphoreSlim.Wait(0)) to prevent overlap - Introduce TryCleanupOnDemand(): cleans on demand (no background thread) - Triggered from DiscardPage (force when free > cap) - Triggered after Extend() requeues pages (signal + on next tick) - Lightweight tick every OPS_CLEANUP_STEP ops (default 256) - Eviction policy: idle + batch (DEFAULT_IDLE=60s, DEFAULT_BATCH=128) - Stamp freed timestamp (UTC ticks) when moving readable -> free - DiscardPage/Extend/Clear now set page.Timestamp - PageBuffer: atomic eviction guard (TryBeginEvict/MarkReusable) to avoid races - Clear(): requeue readable pages, return count, wake cleanup if over cap - Dispose(): block new triggers, wait any running cleanup, dispose lock - Conservative defaults: MaxFreePages=200, Idle=60s, Batch=128, Interval=30s - No public API changes Refs: litedb-org#1756, litedb-org#2619, RFC litedb-org#2647
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zalza13
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Summary
This PR introduces the first round of improvements for the new in-memory cache in LiteDB 5.
Goal: make the cache more predictable, configurable, and robust under heavy concurrent load, while keeping all tests stable.
Key changes
Volatile on scalar tuning fields
_maxFreePages,_cleanupBatchSize,_extendsasvolatileto improve visibility across threads._idleBeforeEvict,_minCleanupInterval) remain asTimeSpan(structs cannot bevolatile).Safer on-demand cleanup triggers
NewPage()andGetWritablePage()to avoid interfering with segment extension andUniqueIDsequencing (fixes the failingCache_UniqueIDNumberingtest).GetReadablePage()(hot read path),DiscardPage()(when pages are freed),Clear()(manual cleanup),_maxFreePages(forced).SemaphoreSlim) with batched eviction and idle policy.Accurate comments & readability
Cleanup()docs to reference_cleanupBatchSizeand_idleBeforeEvict(instead of stale constants).Profiles groundwork
CacheProfile { Mobile, Desktop, Server }andApplyProfile(profile).// TODOmarker left in code).Motivation
LiteDB is often used in embedded scenarios with high concurrency and limited resources.
These changes make cache tuning safer and clearer without adding locking overhead or altering public APIs.
Impact
Related
Next steps
CacheProfileselection via engine parameter (Etapa 2).Checklist
dev-stagingNotes for reviewers