perf: restore UNION ALL pagination for /events/past#2682
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…memory sort Extract fetch_upcoming_events and fetch_past_events into two new methods: - paginated_events(upcoming:) — builds a UNION ALL across workshops, meetings, and events with LIMIT/OFFSET at the database level - load_events(rows) — fetches only the 20 visible rows with full eager loading, preserving UNION sort order Previously, all past workshops (~1100) were loaded into AR objects and sorted/paginated in Ruby. Now only the current page's 20 rows ever leave the database. Benchmark (first load / cached): Past events page: 11.3s → 1.3s DB queries count: ~119 → 118 (same — view N+1s unchanged) Allocations: 25M → 2.9M (cached)
This was referenced Jul 2, 2026
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Problem
The
/events/pastpage times out on Heroku (503) because it loads all past workshops (~2,500), events (~250), and meetings (~50) into ActiveRecord objects, sorts them in Ruby, then paginates. This is the same issue described in the original #2666.What happened to the original fix
PR #2666 built a database-level UNION ALL + LIMIT/OFFSET pagination approach, which reduced the page from 11.3s to 1.3s. However, it was accidentally lost during branch cleanup — it was merged into
bullet-n-plus-one-fixesvia #2666, but then that branch was force-pushed before merging tomaster, dropping the UNION ALL commit. Thebullet-n-plus-one-fixesbranch that eventually merged only contained the smaller organisers eager-load fix.This fix
Cherry-picks the original UNION ALL commit (
f775e3bd) from the survivingarel-union-paginationbranch, then applies the production fix that was learned later::organisersfromEvent.includesandMeeting.includesinload_events, because those models'organisersscope generates SQL without properly joiningpermissions, causingPG::UndefinedTableon production data (fixed in39da6926on master).:organisersonWorkshop.includes, because Workshop's complex associations forceeager_load(LEFT JOINs), which correctly includes the permissions table.:venuetoMeeting.includesand:hosttoWorkshop.includesto match the current master's eager loading pattern.How it works
paginated_events(upcoming:)— builds an Arel UNION ALL query across Workshops, Meetings, and Events with LIMIT/OFFSET at the database level. Only 20(id, event_type)pairs leave the database.load_events(rows)— fetches full ActiveRecord objects for just those 20 rows with eager loading, preserving the UNION sort order.Verification
spec/controllers/events_controller_spec.rb— 4 examples, all passingspec/features/listing_events_spec.rb— 4 examples, all passing