Hotfix(emergency): replace joined Count() aggregates with per-relation subqueries - #2824
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…ubqueries - Three Count(distinct=True) annotations joined in one query fanned out to 9M+ rows for large events, forcing a disk-spilled sort (504s in prod).
szabozoltan69
approved these changes
Sep 7, 2026
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Quick and great solution! |
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Problem
GET /api/v2/emergency/{id}/was timing out (504) for events with a lot of related data. Root cause:EmergencyViewset.get_queryset()computed 3 counts (projects, surge alerts, active deployments) usingCount(distinct=True)on 3 separate relations inside one query. Joining unrelated one-to-many relations multiplies rows instead of adding them — for event 5854 that's 98 × 302 × 330 = 9.7 million rows generated just to get 3 numbers, forcing Postgres to sort/group all of it (spilled 6.9 GiB to disk).Fix
Replaced the 3 joined
Count()aggregates with 3 independent correlated subqueries (one per count, no cross-joining). Same result, no row explosion.Before / After (event 5854)
Before / After (event 6646, smaller: old code could finish here)
Values identical before/after: confirms this is a performance fix only, no behavior change.