perf: sign a run once at ingest instead of on every review - #376
perf: sign a run once at ingest instead of on every review#376nGervasyuk wants to merge 3 commits into
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Measured on production: opening "Approve variations" spends ~4.5s in matchingSiblings before a single thumbnail is requested. For a screen with 34 locales that call fetches 70 full-size screenshots back out of S3 and decodes them, eight at a time. The concurrency bound added with the worker pool was chosen to protect memory and CPU; on S3 the work is network-bound, so eight is simply the number of round trips it waits on. None of that has to happen at review time. The diff already decodes both screenshots at ingest, so the signature is now produced by that same pass and stored on the run. Grouping a screen becomes a column read. - computePixelmatchDiff optionally returns the signature, computed from the images it has already decoded and ignore-masked. Both paths call one signatureOfDecoded, and a test pins the fused answer to be identical to the standalone job's — if they drifted, stored signatures would silently stop matching computed ones and variations would stop grouping. - It is asked for on every comparison rather than only when the project has bulk approve switched on, so turning the flag on later does not leave a build's runs unsigned. - saveDiffResult writes it, and always overwrites: recomputing a diff after the reviewer edits the ignore areas must not leave the old signature describing a change that no longer exists. - Runs with nothing stored — ingested before this, or compared by something other than pixelmatch — fall back to the existing worker-pool path, so no backfill is needed and old builds keep working. The column is nullable with no default, so the migration is catalogue-only: no table rewrite, no long lock on a TestRun table holding a hundred builds.
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Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review. 📝 WalkthroughWalkthroughThe diff pipeline computes optional pixelmatch change signatures, stamps them with comparison settings, stores them on ChangesChange signature flow
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: ⚪ Minimal · up to This change persists pixelmatch change signatures during ingest and reuses only valid, settings-matched values during review. Invalid, older, and unsupported signatures continue to recompute, with no remaining merge-blocking risk identified. Sequence Diagram(s)sequenceDiagram
participant PixelmatchService
participant DiffWorkerPool
participant computePixelmatchDiff
participant saveDiffResult
participant TestRun
participant getChangeSignature
PixelmatchService->>DiffWorkerPool: request diff with withSignature true
DiffWorkerPool->>computePixelmatchDiff: compute diff and signature
computePixelmatchDiff-->>DiffWorkerPool: return diff and optional signature
DiffWorkerPool-->>PixelmatchService: return worker output
PixelmatchService->>saveDiffResult: pass stamped changeSignature
saveDiffResult->>TestRun: store JSON signature or null
getChangeSignature->>TestRun: read stored signature
TestRun-->>getChangeSignature: return valid signature or trigger recomputation
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✅ Passed checks (4 passed)
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Actionable comments posted: 1
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Inline comments:
In `@src/test-runs/test-runs.service.ts`:
- Around line 306-308: Update the change-signature persistence and retrieval
flow around parseStoredSignature and signatureOfDecoded to store a fingerprint
of the pixelmatch threshold/includeAA configuration, and recompute the signature
when the stored fingerprint differs from the current imageComparisonConfig.
Preserve reuse when configurations match, and add a regression test covering
configuration changes and variation grouping.
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prisma/migrations/20260904120000_add_test_run_change_signature/migration.sqlprisma/schema.prismasrc/_data_/index.tssrc/compare/libs/pixelmatch/pixelmatch.core.spec.tssrc/compare/libs/pixelmatch/pixelmatch.core.tssrc/compare/libs/pixelmatch/pixelmatch.service.spec.tssrc/compare/libs/pixelmatch/pixelmatch.service.tssrc/compare/libs/pixelmatch/signature.core.tssrc/test-runs/diffResult.tssrc/test-runs/test-runs.service.spec.tssrc/test-runs/test-runs.service.ts
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A signature only means anything under the threshold it was computed with. The in-memory memo has always keyed on threshold and includeAA; when the same value started being persisted, that guard was not carried over. So a project whose imageComparisonConfig is edited after a build was ingested could compare a stored signature, taken under the old settings, against a sibling's computed fresh under the new ones. Nothing breaks loudly: variations simply stop grouping as well as they did, and the reviewer has no way to tell why. The settings now travel with the signature, and a stored one whose settings no longer match the project's is discarded — which falls back to computing it, exactly as for a run that never had one. The optimisation now knows what it was computed under. Found by CodeRabbit on Visual-Regression-Tracker#376.
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🟡 Changes recommended
Type definitions and stored-signature parsing need tightening (notably DiffResult nullability and signature validation) to avoid incorrect runtime assumptions and corrupted-data grouping.
Once you've addressed the issues Copilot identified, you can request another Copilot review.
Pull request overview
This PR improves Approve variations performance by computing and persisting a “change signature” during ingest (alongside diff generation) so variation grouping can read a stored value instead of re-fetching and decoding many sibling screenshots at review time.
Changes:
- Add
changeSignaturepersistence toTestRunand write it whenever a diff is saved (overwriting withnullwhen absent). - Fuse signature computation into the pixelmatch diff path by reusing a shared
signatureOfDecodedimplementation to avoid duplicate decodes. - Update matching logic/tests to prefer stored signatures and fall back to worker-pool computation for older/unsupported runs.
File summaries
| File | Description |
|---|---|
| src/test-runs/test-runs.service.ts | Reads stored signatures when valid; persists signatures in saveDiffResult; adds parser for stored JSON. |
| src/test-runs/test-runs.service.spec.ts | Adds coverage for signature persistence, overwrite-to-null, stored-signature grouping, and fallback behavior. |
| src/test-runs/diffResult.ts | Introduces StampedSignature and extends DiffResult with changeSignature. |
| src/compare/libs/pixelmatch/signature.core.ts | Extracts signatureOfDecoded so diff + standalone signature share one implementation. |
| src/compare/libs/pixelmatch/pixelmatch.core.ts | Adds withSignature option and emits signature in the diff worker output when requested. |
| src/compare/libs/pixelmatch/pixelmatch.core.spec.ts | New spec ensuring fused signature matches standalone signature and doesn’t affect diff behavior. |
| src/compare/libs/pixelmatch/pixelmatch.service.ts | Always requests withSignature and stamps signature with comparison settings into DiffResult. |
| src/compare/libs/pixelmatch/pixelmatch.service.spec.ts | Tests plumbing: pool is called with withSignature, result carries stamped signature when present. |
| src/data/index.ts | Updates test-run factory defaults to include changeSignature: null. |
| prisma/schema.prisma | Adds nullable changeSignature column to TestRun. |
| prisma/migrations/20260904120000_add_test_run_change_signature/migration.sql | Adds changeSignature TEXT with nullable/no-default migration. |
Review details
Suppressed comments (1)
src/test-runs/diffResult.ts:20
- DiffResult is typed as if all fields are always present (e.g., diffName: string), but the implementation frequently uses null/undefined (e.g., NO_BASELINE_RESULT sets diffName: null and status: undefined). This makes the type inconsistent with actual runtime values and encourages unsafe assumptions downstream.
status: TestStatus;
diffName: string;
pixelMisMatchCount: number;
diffPercent: number;
isSameDimension: boolean;
- Files reviewed: 11/11 changed files
- Comments generated: 2
- Review effort level: Lite
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| const parsed: StampedSignature = JSON.parse(stored); | ||
| if (!Array.isArray(parsed?.signature) || parsed.signature.length === 0) { | ||
| return null; | ||
| } | ||
| const sameConfig = parsed.threshold === config.threshold && parsed.includeAA === config.ignoreAntialiasing; | ||
| return sameConfig ? parsed.signature : null; | ||
| } catch (error) { | ||
| logger.warn(`Ignoring unreadable stored change signature: ${error}`); | ||
| return null; | ||
| } |
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Right, and it is the same failure the config stamp on this PR was added for, one level down.
parseStoredSignature accepted any non-empty array. A stored vector of one length compared against a current one of another walks off the end of the shorter, and cosineSimilarity scores over undefined entries — it returns a number, and the number means nothing. Nothing throws; grouping just quietly gets worse, which is exactly the mode that is hard to notice and harder to attribute.
The realistic way in is not a corrupt row but a code change: COLOR_BUCKETS_PER_CHANNEL is a constant, and moving it turns every signature already in the database into the wrong shape.
Fixed in b9b7c42 — SIGNATURE_LENGTH is exported from signature.core and the stored value must match it and be all finite numbers, otherwise it is recomputed. Two tests cover it, and they caught something real on the way in: my earlier fixtures used two-element vectors, which the new check rightly rejects, so they now use full-length histograms.
| // Always written, never merged: a recomputed diff — after the | ||
| // reviewer edits the ignore areas, say — must not leave the previous | ||
| // signature behind describing a change that no longer exists. | ||
| changeSignature: diffResult?.changeSignature ? JSON.stringify(diffResult.changeSignature) : null, | ||
| }, |
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Fair — fixed in b9b7c42, though only the typing half.
The parameter is genuinely nullable: a comparison that produced nothing clears the row back to new, the body has always been written for that, and a test passes null outright. The signature said DiffResult, which is the sort of small untruth that invites a real one later, so it now says DiffResult | null.
I left the diffResult && ... guards as they are. They read as redundant next to optional chaining, but rewriting assignments whose semantics are "undefined leaves the column untouched, null clears it" is a change with real behavioural surface for a stylistic gain — and this PR is already carrying a schema migration. Worth doing on its own, not as a rider here.
A signature is a fixed-length histogram, and parseStoredSignature accepted any non-empty array as one. Comparing a stored vector of one length against a current one of another walks off the end of the shorter and scores the similarity over undefined entries — it returns a number, and the number means nothing. Nothing throws; grouping just quietly gets worse. That is the same failure the config stamp was added for, one level down: if COLOR_BUCKETS_PER_CHANNEL is ever changed, every signature already in the database becomes the wrong shape. The length and element types are now checked against what this build produces, so a stored signature that no longer fits is recomputed instead of half-used. Also types saveDiffResult's parameter as nullable. It genuinely is — a comparison that produced nothing clears the row back to "new", the body has always handled that, and a test passes null — but the signature claimed otherwise, which is the sort of small lie that invites a real one later. Both found by Copilot on Visual-Regression-Tracker#376.
The measurement
On a production build of ~11k runs, opening Approve variations spends ~4.5 s inside
matchingSiblingsbefore a single thumbnail is even requested. From the network panel, that one request is the long bar; everything after it is images.For a screen with 34 locales, that call fetches 70 full-size screenshots back out of S3 and decodes them, eight at a time. The concurrency bound introduced with the worker pool (#372) was chosen to protect memory and the shared queue — correct when the work is CPU-bound on local disk. On S3 it is network-bound, so eight is simply the number of round trips the reviewer waits on: 70 / 8 ≈ 9 pairs × ~500 ms ≈ the 4.5 s observed.
The fix
None of that has to happen at review time. The diff already decodes both screenshots at ingest. The signature is now produced by that same pass and stored on the run, so grouping a screen becomes a column read.
computePixelmatchDiffoptionally returns the signature, computed from the images it has already decoded and ignore-masked. Both it and the standalone job call onesignatureOfDecoded, and a test pins the fused answer to be identical to the standalone one. That test is the point of the change: if the two drifted, stored signatures would silently stop matching computed ones and variations would quietly stop grouping.saveDiffResultwrites it, and always overwrites. Recomputing a diff after the reviewer edits the ignore areas (which goes throughcalculateDiff) must not leave the previous signature behind describing a change that no longer exists.Old builds
Runs with nothing stored — ingested before this, or compared by lookSame/odiff/vlm — fall back to the existing worker-pool path, memoized as before. No backfill is required and no build stops working; new builds are simply fast. A backfill could be added later if the wait on existing builds is worth it.
The migration
changeSignature TEXT— nullable, no default, so on Postgres 11+ this is a catalogue-only change: no table rewrite and no long lock on aTestRuntable holding a hundred builds' worth of runs.Storage is bounded by how many runs actually carry a change: the signature is null when nothing changed, so only runs with a diff pay ~450 bytes.
Tests
Watched failing first, at three levels:
pixelmatch.core.spec— the fused signature equals the standalone one; absent when not asked for, when the screenshots are identical; the diff itself is unaffected.pixelmatch.service.spec— the plumbing only (Pixelmatch is mocked in that file, so correctness lives in the core spec): the pool is asked withwithSignature, and what comes back lands in the result.test-runs.service.spec— grouping runs off stored signatures without asking the compare service at all, falling back per-run when one is missing, and persistence including the overwrite-with-null case.All 37 backend spec files pass. (The full parallel run trips over a missing Prisma engine binary in the sandbox, identically on
master, so specs were run one at a time.)tsc, eslint and prettier clean; eslint's 5 warnings are the same onesmasterhas.Summary by CodeRabbit
New Features
Bug Fixes