Replace SubscribeEvictions with IRecordTriggers

[badrishc]

Replace SubscribeEvictions with IRecordTriggers.OnEvict for heap-size tracking

Garnet's CacheSizeTracker used LogAccessor.SubscribeEvictions to drive a LogSizeTracker.OnNext observer that, on every page eviction, allocated a scan iterator and walked the page to sum MemoryUtils.CalculateHeapMemorySize over each non-null / non-closed record. This is heavyweight for a hot path (buffer-pool allocation, iterator bookkeeping, epoch resume/suspend, and a virtual dispatch per page).

This PR migrates the per-page heap-size decrement onto the per-record IRecordTriggers.OnEvict hook introduced in #1695, which the object allocator already walks during EvictRecordsInRange. That lets us collapse the "scan iterator + observer + sum" path into a single per-record callback directly on the record we would have visited anyway.

Tsavorite changes

• Add EvictionSource { MainLog, ReadCache } and thread it through IRecordTriggers.OnEvict, IStoreFunctions.OnEvict, and IAllocator.EvictRecordsInRange. Garnet uses this to route decrements to the correct counter (AddHeapSize vs AddReadCacheHeapSize).
• Add AllocatorSettings.IsReadCache and AllocatorBase.IsReadCache, set to true by Tsavorite.cs when constructing the read-cache allocator. This is the cleanest way to distinguish the two allocators at OnPagesClosedWorker time without relying on the evictCallback sentinel.
• AllocatorBase.EvictPageForRecovery now also routes through the per-record EvictRecordsInRange when storeFunctions.CallOnEvict is set. The legacy MemoryPageScan(observer) path is preserved as a fallback for consumers that still use SubscribeEvictions.
• Collapse AllocatorBase's constructor to accept AllocatorSettings directly instead of unpacking individual fields at each concrete allocator (ObjectAllocatorImpl, SpanByteAllocatorImpl, TsavoriteLogAllocatorImpl).

Garnet changes

• GarnetRecordTriggers.CallOnEvict is now gated on cacheSizeTracker != null. OnEvict(ref LogRecord, EvictionSource) computes MemoryUtils.CalculateHeapMemorySize(in logRecord) and dispatches to AddHeapSize(-size) or AddReadCacheHeapSize(-size) based on the source.
• CacheSizeTracker.Initialize replaces the two SubscribeEvictions calls with SetLogSizeTracker calls so the fast-path size tracking during TryCopyToTail, TryCopyToReadCache, and object-page growth (UpdateSize, IncrementSize) continues to work unchanged.

Parity

Behavior at every record state encountered during page eviction is bit-for-bit identical to the prior SubscribeEvictions path:

Record state	Old path (iterator)	New path (per-record)	Delta
Valid, !Sealed, !Tombstone, !IsNull	yielded → -CalculateHeapMemorySize	OnEvict → -Calculate...	same
IsNull	skipped by iterator	skipped by filter	0
SkipOnScan (Invalid or Sealed)	skipped by iterator	skipped by filter	0
Tombstone (post-delete, already ValueIsInline)	yielded → 0 via !Info.Tombstone	skipped by filter → 0	0

Tombstones converge via two independent mechanisms (the old relies on the if (!Info.Tombstone) guard inside CalculateHeapMemorySize; the new short-circuits in the filter), so both yield 0 contribution as required given the delete-site OnDispose(Deleted) already decremented the tracker.

Testing

All tests pass on net10.0 Debug:

• CacheSizeTrackerTests 2/2
• RespListTests.ListPushPopStressTest (10 repetitions) ✓
• RespListTests, RespHashTests, RespSetTests, RespSortedSetTests: 467/467
• Tsavorite DeleteDisposeTests + ReadCacheTests: 228/228, 14 skipped
• Clean build on both Garnet.slnx and Tsavorite.slnx (0 warnings, 0 errors).

Future TODO

The only residual subtlety worth flagging (and pre-existing to this PR) is that a TryCopyToTail produces two records sharing the same IHeapObject via TryCopyFrom. If a subsequent in-place RMW on the dest mutates that shared object (growing from X to Y), CalculateHeapMemorySize at source-evict time will return the current Y, not the originally-added X — so the source's eviction under-/over-decrement scales with post-copy mutation. The old observer-iterator path reads the same field at the same time, so it has exactly the same behavior.

[Copilot]

Pull request overview

This PR migrates Garnet heap-size accounting on page eviction from the SubscribeEvictions iterator/observer scan path to Tsavorite’s per-record IRecordTriggers.OnEvict callback, while also threading an EvictionSource (main log vs read cache) through the eviction APIs.

Changes:

• Introduces EvictionSource { MainLog, ReadCache } and threads it through IRecordTriggers.OnEvict, IStoreFunctions.OnEvict, and IAllocator.EvictRecordsInRange.
• Adds AllocatorSettings.IsReadCache / AllocatorBase.IsReadCache to tag eviction callbacks with the correct source.
• Updates Garnet CacheSizeTracker wiring to use SetLogSizeTracker (fast-path size tracking) and moves eviction decrements to GarnetRecordTriggers.OnEvict.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
libs/storage/Tsavorite/cs/src/core/Index/Tsavorite/Tsavorite.cs	Marks the read-cache allocator via AllocatorSettings.IsReadCache = true.
libs/storage/Tsavorite/cs/src/core/Index/StoreFunctions/StoreFunctions.cs	Updates store-functions eviction forwarding to include EvictionSource.
libs/storage/Tsavorite/cs/src/core/Index/StoreFunctions/IStoreFunctions.cs	Updates OnEvict signature to include EvictionSource.
libs/storage/Tsavorite/cs/src/core/Index/StoreFunctions/IRecordTriggers.cs	Adds EvictionSource enum and updates IRecordTriggers.OnEvict signature/docs.
libs/storage/Tsavorite/cs/src/core/Allocator/TsavoriteLogAllocatorImpl.cs	Switches allocator base ctor usage to pass AllocatorSettings directly.
libs/storage/Tsavorite/cs/src/core/Allocator/TsavoriteLogAllocator.cs	Updates EvictRecordsInRange signature to include EvictionSource.
libs/storage/Tsavorite/cs/src/core/Allocator/SpanByteAllocatorImpl.cs	Switches allocator base ctor usage to pass AllocatorSettings directly.
libs/storage/Tsavorite/cs/src/core/Allocator/SpanByteAllocator.cs	Updates EvictRecordsInRange signature to include EvictionSource.
libs/storage/Tsavorite/cs/src/core/Allocator/ObjectAllocatorImpl.cs	Threads EvictionSource into per-record eviction callbacks to storeFunctions.OnEvict.
libs/storage/Tsavorite/cs/src/core/Allocator/ObjectAllocator.cs	Updates wrapper to pass EvictionSource through EvictRecordsInRange.
libs/storage/Tsavorite/cs/src/core/Allocator/IAllocator.cs	Updates EvictRecordsInRange contract to include EvictionSource.
libs/storage/Tsavorite/cs/src/core/Allocator/AllocatorSettings.cs	Adds IsReadCache flag for allocator tagging.
libs/storage/Tsavorite/cs/src/core/Allocator/AllocatorBase.cs	Stores IsReadCache, passes EvictionSource into eviction calls, and updates recovery eviction path.
libs/server/Storage/SizeTracker/CacheSizeTracker.cs	Replaces SubscribeEvictions with SetLogSizeTracker for internal size tracking.
libs/server/Storage/Functions/GarnetRecordTriggers.cs	Enables CallOnEvict and implements OnEvict(ref LogRecord, EvictionSource) heap-size decrement routing.

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[Copilot]

CallOnEvict is currently gated on cacheSizeTracker != null, but GarnetServer.CreateStore always constructs a CacheSizeTracker and passes it into GarnetRecordTriggers even when heap-size tracking is disabled (only sets sizeTracker = cacheSizeTracker when LogMemorySize/ReadCacheMemorySize > 0). This makes CallOnEvict effectively always true and will invoke OnEvict on every page eviction, doing MemoryUtils.CalculateHeapMemorySize work even when there is no tracker initialized (and the decrement becomes a no-op). Consider gating on cacheSizeTracker.IsInitialized (or mainLogTracker/readCacheTracker != null) so eviction callbacks are only enabled when size tracking is actually configured.

[badrishc]

Heap-Size Accounting: Record Lifecycle Trace

All destruction-side heap accounting is internal to Tsavorite via logSizeTracker. GarnetRecordTriggers is a no-op for accounting — triggers remain available for app-level resource cleanup (e.g. IDisposable.Dispose on value objects holding external resources).

Accounting Model

Creation (+value): Session functions (PostInitialUpdater/Writer, PostCopyUpdater, InPlaceUpdater) emit +value via cacheSizeTracker.AddHeapSize. Only the app knows the heap size of a newly created value.

Destruction (−key, −value): Tsavorite handles all decrements internally:

• OnDispose(Deleted): −value via logSizeTracker (before tombstone is set)
• EvictRecordsInRange: −(key+value) for non-tombstoned records, −key for tombstoned records
• CopyUpdate eager clear: −valueObject via logSizeTracker + IHeapObject.Dispose()
• TryCopyToTail / TryCopyToReadCache: +(key+value) via logSizeTracker.UpdateSize (balanced by eviction)

Lifecycle Trace

Event	Tsavorite internal accounting	Trigger	Status
Mutable Delete	OnDispose(Deleted): −value. Tombstone set after. Eviction: −key.	No-op	✅
Immutable Delete	OnDispose(Deleted) on source: −value. Source sealed. Eviction: −key (value already cleared).	No-op	✅
RMW ExpireAndStop IPU	OnDispose(Deleted): −value. Tombstone set after. Eviction: −key.	No-op	✅
RMW ExpireAndResume IPU	OnDispose(Deleted): −value. PostInitialUpdater: +value (new). Eviction: −(key+value).	+value	✅
RMW ExpireAndStop NCU (elidable)	OnDispose(Deleted): −value. Tombstone set. Elided → freelist clears key. Eviction skips (invalid).	No-op	✅
RMW ExpireAndStop NCU (non-elidable)	OnDispose(Deleted) on source: −value. Eviction of source: −key. New tombstone at tail (no heap).	No-op	✅
RMW ExpireAndResume NCU/CU	OnDispose(Deleted) on source: −value. Source eviction: −key. New record: +value.	+value	✅
RMW ExpireAndStop CU	OnDispose(Deleted) on source: −value. Source sealed. Eviction: −key. Tombstone at tail (no heap).	No-op	✅
CopyUpdate (ClearSource=true)	Internal: −valueObject + Dispose(). Source sealed. Eviction: −key.	PCU: +value	✅
CopyUpdate (ClearSource=false, checkpoint)	Source keeps value object, sealed. Eviction: −(key+value).	PCU: +value	✅
CopyUpdate (source in readonly)	Source not sealed. Eviction: −(key+value).	PCU: +value	✅
Elision after delete	OnDispose(Deleted): −value. Freelist transfer clears key. Eviction skips (invalid).	No-op	✅
Revivification (to freelist)	ClearHeapFields(clearKey=true). No tracker decrement (prior Deleted already did −value).	No-op	✅
Revivification (from freelist)	Zeros all fields. Session fn: +value for new content.	+value	✅
CAS failure	ClearHeapFields frees memory. No tracker decrement (session fn never added +).	No-op	✅
WrongType IPU	No tombstone. No OnDispose. Record intact.	No-op	✅
Page eviction (non-tombstoned)	−CalculateHeapMemorySize() (key+value).	No-op	✅
Page eviction (tombstoned)	−key overflow only (value already decremented at delete site).	No-op	✅
Recovery eviction	Same as runtime eviction.	No-op	✅
TryCopyToTail	+(key+value) via logSizeTracker.UpdateSize. Balanced by eviction.	No session fn	✅
TryCopyToReadCache	+(key+value) via readcacheBase.logSizeTracker.UpdateSize. Balanced by eviction.	No session fn	✅
Disk read (pending IO)	No tracker impact (transient record).	No-op	✅
Scan (in-memory / disk)	No tracker impact.	No-op	✅
Checkpoint serialization	No tracker impact (temporary clone).	N/A	✅