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fetch exposures from counter in db instead of scanning and counting - #3420
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danoswaltCL wants to merge 1 commit into
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danoswaltCL wants to merge 1 commit into
danoswaltCL wants to merge 1 commit into
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🟡 Changes recommended
Exposure counters can permanently undercount because synchronized databases skip the backfill and legacy writers can add exposures during or after backfilling without updating the counter.
2 open issues
What changed in this PR
Replaces exposure-table scans in paginated feature-flag reads with maintained per-flag counters to reduce list latency.
Changes:
- Adds a counter entity and migration that backfills existing exposure totals.
- Atomically increments counters for newly inserted exposures and uses them in paginated responses.
- Updates unit tests and documents counter consistency and repair procedures.
| File | Description |
|---|---|
packages/backend/test/unit/services/FeatureFlagService.test.ts |
Tests count attachment and zero defaults. |
packages/backend/test/unit/repositories/FeatureFlagExposureRepository.test.ts |
Tests SQL construction, counter lookup, and empty inputs. |
packages/backend/src/database/migrations/1794418860625-featureFlagExposureCount.ts |
Creates and backfills the counter table with cascade deletion. |
packages/backend/src/api/services/FeatureFlagService.ts |
Reads maintained counts for paginated flags. |
packages/backend/src/api/repositories/FeatureFlagExposureRepository.ts |
Adds atomic exposure/count writes and counter lookups. |
packages/backend/src/api/models/FeatureFlagExposureCount.ts |
Defines the separate per-flag counter entity. |
packages/backend/src/api/models/FeatureFlag.ts |
Converts exposureCount to a plain response property. |
packages/backend/CLAUDE.md |
Documents counter maintenance, invariants, and reconciliation. |
Review effort: Balanced
| return { | ||
| ...featureFlag, | ||
| // A flag with no exposures yet has no counter row | ||
| exposureCount: exposureCounts.get(featureFlag.id) ?? 0, |
Comment on lines
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| INSERT INTO "feature_flag_exposure_count" ("featureFlagId", "count") | ||
| SELECT "featureFlagId", COUNT(*)::int | ||
| FROM "feature_flag_exposure" | ||
| GROUP BY "featureFlagId" |
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The migration backfills existing counts.
Also to note this should have minimal impact even though it moves a db operation to a frequent call; only first-time callers will be registering an exposure and thus incrementing the counter, which can't be much added work, but we should keep it in my for performance tests.