Reduce sync work: faster snapshot projection + benchmarks - #86
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Previously AddSnapshots projected each snapshot by calling FindAsync per entity, which issued one database query per snapshot (and, on an initial sync of new data, every query returned null after a round-trip). Pre-load the projected rows that already exist for the batch with a single tracked query per object type. ProjectSnapshot then resolves existing entities from the change tracker and skips the lookup entirely for entities that have no projected row yet, collapsing N queries down to roughly one per distinct object type. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_019zEmz7jPRPF6Lv8h6YAWBW
Adds a BenchmarkDotNet suite that measures CrdtRepository.AddSnapshots on its own, across 7 workloads mirroring DataModelSyncBenchmarks. Expensive DB seeding runs once in a template DB; each iteration forks the DB and recomputes the snapshot batch so no EF-tracked state leaks across iterations. - SnapshotWorker.ComputeSnapshotsToPersist: returns the exact snapshot list UpdateSnapshots would persist, without writing it. - DataModelTestBase: internal CreateRepository() and CrdtConfig accessors. - BenchmarkWorkloadBuilders: shared commit builders extracted from DataModelSyncBenchmarks (+ BuildUpdateExisting). - Program.cs: run both suites via BenchmarkSwitcher (handles --filter/args). - Remove leftover Console.WriteLine debug lines from AddSnapshots. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Two experimental fast AddSnapshots implementations that keep the EF snapshot insert unchanged but populate projected tables with raw INSERT ... ON CONFLICT upserts instead of going through EF's change tracker: - FAST: one upsert command per entity row - FAST_JSON: one command per entity type, rows passed as a single JSON array expanded with SQLite json_each/json_extract FastProjection derives table/column names, primary key, the SnapshotId shadow FK, and value converters from the EF model (no per-entity code). It dedups to the latest snapshot per entity, runs deletes before upserts (children-first) then upserts (parents-first) for FK/unique-constraint safety, and reuses the caller's transaction. CrdtRepository.AddSnapshots now selects via #if FAST_JSON / #elif FAST / #else. Program.cs adds a third FAST_JSON benchmark job and DataModelSyncBenchmarks enables [MemoryDiagnoser]. Benchmarks (CreateWords, 1000): both fast paths ~35% faster and ~32% fewer allocations than baseline; per-query vs JSON-batch shows no measurable difference against in-memory SQLite. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
The JSON-batch projection benchmarked identically to the per-query path against in-memory SQLite (same time and allocations), so remove it and keep only the per-query raw-SQL upsert path. FastProjection loses the useJsonBatch parameter and all json_each/json_extract code; CrdtRepository.AddSnapshots collapses to #if FAST / #else; the benchmark drops the FAST_JSON job. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Remove the EF change-tracker slow path and the #if FAST conditional so AddSnapshots always uses FastProjection. Deletes the now-dead slow-path helpers (ProjectSnapshot, GetEntityEntry, LoadExistingEntityIds, LoadExistingEntities). The benchmark collapses to a single job since FAST vs DEFAULT are now identical. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
FastProjection is now an injected singleton (registered in AddCrdtDataCore and resolved into CrdtRepository via ActivatorUtilities) instead of a static class. Its per-type projected-table SQL metadata cache moves from a static field onto an internal ConcurrentDictionary on CrdtConfig, so it's shared across repositories/contexts and tied to config lifetime. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review. 📝 WalkthroughWalkthroughThe change adds model-aware projection persistence, projected-entity notifications, snapshot computation support, validation tests, performance tests, and BenchmarkDotNet coverage for sync and snapshot insertion workloads. ChangesProjection and snapshot pipeline
Projection and interceptor validation
Benchmark harness
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~45 minutes Change: Refactor Sequence Diagram(s)sequenceDiagram
participant SyncCaller
participant CrdtRepository
participant SnapshotWorker
participant FastProjection
participant ProjectedEntityInterceptor
SyncCaller->>CrdtRepository: AddRangeFromSync
CrdtRepository->>SnapshotWorker: Compute snapshots
SnapshotWorker-->>CrdtRepository: Return snapshot batch
CrdtRepository->>FastProjection: AddSnapshotsRawAsync
FastProjection-->>CrdtRepository: Return projected entity changes
CrdtRepository->>ProjectedEntityInterceptor: OnProjectedEntitiesChanged
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# Conflicts: # src/SIL.Harmony/Config/HarmonyConfig.cs # src/SIL.Harmony/SnapshotWorker.cs
Notify DI interceptors and HarmonyConfig.OnProjectedEntitiesChanged after projected SQL with the latest upsert or delete per entity.
Keep the slnx migration from main and include SIL.Harmony.Benchmarks in the solution.
Main now uses Microsoft.Testing.Platform, so solution-wide dotnet test was launching the Benchmarks exe and failing on unknown MTP flags.
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In `@src/SIL.Harmony/Db/FastProjection.cs`:
- Line 219: Update AddSnapshotsRawAsync and the SQL construction around
InsertSql to avoid unconditionally emitting SQLite-specific ON CONFLICT/excluded
syntax. Select provider-specific upsert SQL based on the configured EF Core
provider, or reject EnableProjectedTables for unsupported providers, and add
integration coverage for every provider declared as supported.
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harmony.slnxsrc/SIL.Harmony.Benchmarks/AddSnapshotsBenchmarks.cssrc/SIL.Harmony.Benchmarks/BenchmarkWorkloadBuilders.cssrc/SIL.Harmony.Benchmarks/DataModelSyncBenchmarks.cssrc/SIL.Harmony.Benchmarks/Program.cssrc/SIL.Harmony.Benchmarks/SIL.Harmony.Benchmarks.csprojsrc/SIL.Harmony.Tests/DataModelTestBase.cssrc/SIL.Harmony.Tests/ProjectedEntityInterceptorTests.cssrc/SIL.Harmony.Tests/SIL.Harmony.Tests.csprojsrc/SIL.Harmony/Config/HarmonyConfig.cssrc/SIL.Harmony/CrdtKernel.cssrc/SIL.Harmony/DataModel.cssrc/SIL.Harmony/Db/CrdtDbContextFactory.cssrc/SIL.Harmony/Db/CrdtRepository.cssrc/SIL.Harmony/Db/FastProjection.cssrc/SIL.Harmony/Db/ICrdtDbContext.cssrc/SIL.Harmony/Db/IProjectedEntityInterceptor.cssrc/SIL.Harmony/SIL.Harmony.csprojsrc/SIL.Harmony/SnapshotWorker.cs
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Addresses review feedback on the raw-SQL projection path: - Scope ProjectedTableInfoCache by (IModel, Type) so a config shared across multiple EF models/providers can't reuse another model's metadata. - Use the property's relational type-mapping converter instead of GetValueConverter(), and reject models FastProjection can't source (non-SnapshotId shadow properties, TPH discriminators) up front. - Order same-type rows by their self-referencing FK so a referenced row is upserted before the row pointing at it (acyclic; cycles remain unsupported). Each fix has a regression test verified to fail before the change. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
The projected-table upserts use SQLite's INSERT ... ON CONFLICT ... excluded dialect, so fast projection only supports the SQLite provider. Throw a clear NotSupportedException at the projection entry point when projected tables are enabled on any other provider, pointing at HarmonyConfig.EnableProjectedTables. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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⚠️ Performance Alert ⚠️
Possible performance regression was detected for benchmark.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 2.
| Benchmark suite | Current: 1334d81 | Previous: 5e379ef | Ratio |
|---|---|---|---|
SIL.Harmony.Tests.DataModelPerformanceBenchmarks.AddSingleChangePerformance(StartingSnapshots: 0) |
4105166.52 ns (± 667059.817775192) |
1859056.6176470588 ns (± 58820.05785586715) |
2.21 |
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| await repo.DeleteStaleSnapshots(oldestAddedCommit); | ||
| Dictionary<Guid, Guid?> snapshotLookup = []; | ||
| Dictionary<Guid, ObjectSnapshot?> snapshotLookup = []; | ||
| if (commitsToApply.Count > 10) |
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This would be a good time to tweak this:
I'm pretty sure this should consider the change count rather than commit count.
Or maybe we can just totally drop the if. Aren't we doing work that the snapshot-worker will almost definitely have to do anyway? So, even if we only preload 2 snapshots, is that somehow worse than letting the snapshot worker load them on demand?
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I think originally I had the if as a way to keep the normal path (one change) fast. Because it was just looking up the mapping between entity and snapshot then it was actually doing more work than was needed by the snapshot worker. But since it's actually just looking up the snapshot now, it's not doing more work. So yes, we could drop the if now.
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Bringing this back @myieye so it turns out our fast path of adding 1 change is much worse when we do this. Inside SnapshotWorker it can just get the snapshot with a simple get latest snapshot for object query. Which is much much faster than this query which has to get the latest snapshot per entry and compare to commits etc.
The works is per entity id, so I created a new test, take a look at DataModelPerformanceTests.SimpleAddCountChangesPerformanceTest
I tweaked our warmup runs, and so now our normal 1 count test is failing, but we may just need to tweak our ratios again I'm not sure. The surprise here is that it can be faster to run the simple query 100 times, compared to running this query once. SQLite is weird. Not quite sure what to do here yet, but it's still open for question.
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Gotcha. So:
- we probably do want a gate/
if - the gate should be pretty high if it's really that expensive (around 50-150 unique entities?). It makes sense that it's expensive.
- it should actually be gated on the number of unique entity IDs - not commit count or change count
- We could potentially write a benchmark-y test that documents why we choose the number that we do
Small operations are fast enough anyway.
We're only trying to optimize big, slow stuff that actually benefits from a heavy query:
- big syncs
- project downloads (essentially just a big one-way sync)
- syncs that add old commits (which is essentially just another kind of "big" sync)
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ok, it looks like I didn't push the tests I wrote. There's a new perf test now. I put the gate at 220, running in release 200 is actually faster just fetching each snapshot one by one. That might change with #118.
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I think the perf tests are failing due to a change I made in DataModel that we now always query snapshots. |
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See #86 (comment)
Everything else looks good to me.
| await MeasureTime(() => dataModelTest.WriteNextChange(GetChanges(dataModelTest, count)).AsTask()); | ||
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| await StartTrace(); | ||
| var runtimeAddChange10000Snapshots = await MeasureTime(() => dataModelTest.WriteNextChange(GetChanges(dataModelTest, count)).AsTask()); |
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Theoretically GetChanges should probably run outside the measured code.
| internal static readonly ProjectedEntitiesChangedDelegate DefaultOnProjectedEntitiesChanged = | ||
| static _ => ValueTask.CompletedTask; | ||
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| public int PrefetchSnapshotsBreakpoint { get; set; } = 220; //not exactly sure the right number, but 200 is slower with the query, in release builds |
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It would be cool to see your optimization PR fail, because we have a test that documents this as being a reasonable value (neither too high or too low).
Up to you.
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Overview
Reduces the work done during sync (
AddRangeFromSync→SnapshotWorker.UpdateSnapshots→CrdtRepository.AddSnapshots) and adds a benchmark suite to measure it. On theCreateWordsworkload at 10k changes this branch takes sync from ~1.96 s / 976 MB allocated down to ~0.99 s / 538 MB — roughly 2× faster and ~45% less memory.What changed
Snapshot pre-load (
SnapshotWorker/DataModel)UpdateSnapshotsnow bulk-loads the relevant current snapshots (with theirCommit) into a cache keyed by entity id, andSnapshotWorkerreads full snapshots straight from that cache instead of issuing aFindSnapshotDB round-trip per cache hit.Fast raw-SQL projection (
FastProjection, new)INSERT ... ON CONFLICT(pk) DO UPDATE(one upsert per entity row) instead of going through EF's change tracker (FindAsync/SetValues/ graph tracking).SnapshotIdshadow FK, value converters — is derived from the EF model, so there is no per-entity code.FastProjectionis an injectable singleton; its per-type SQL metadata cache lives on an internalConcurrentDictionaryonCrdtConfig, shared across repositories/contexts. This replaces the previous EF change-tracker projection path inCrdtRepository.AddSnapshots, which is removed.Benchmarks (new
SIL.Harmony.Benchmarksproject)DataModelSyncBenchmarks(7 sync workloads) and anAddSnapshotsBenchmarksthat isolates the persist step,[MemoryDiagnoser]enabled. Run withdotnet run -c Release --project src/SIL.Harmony.Benchmarks.Testing
DataModelPerformanceBenchmarkstiming-threshold tests, which also fail onmain(environmental, not caused by this change).Notes for reviewers
ON CONFLICTafter aSELECTneeds the SQLiteWHERE truedisambiguator in the code history — the current per-query path usesVALUES). If other providers are ever targeted,FastProjectionwould need revisiting.Word.AntonymIdpointing at another newWordin the same batch) is not ordered; it's a nullableSET NULLFK and not exercised by current workloads.Summary by CodeRabbit
New Features
Performance
Bug Fixes