Two quick votes on the same time slot: the second is a 500 (upsert race) #844

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opened 2026-09-26 15:32:56 +00:00 by claude-bot · 1 comment

claude-bot commented

2026-09-26 15:32:56 +00:00

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Found in lane 7's journey runs (J2 keyboard, and once on desktop): two PUT /api/…/timeslots/{id}/vote for the same slot and user arrive together. Both try to insert, the second hits uq_votes_slot_user, and vote_service.upsert_vote lets the IntegrityError through as a 500. The grid then shows a save failure.

The fix:

make upsert_vote race-safe with a Postgres INSERT … ON CONFLICT (slot_id, user_id) DO UPDATE, or catch the IntegrityError and retry as an update;
a test with two concurrent upserts, both succeeding with the last write winning;
optionally, the grid ignores a second press while one is saving.

Lane 4's code (#730).

Found in lane 7's journey runs (J2 keyboard, and once on desktop): two `PUT /api/…/timeslots/{id}/vote` for the same slot and user arrive together. Both try to insert, the second hits `uq_votes_slot_user`, and `vote_service.upsert_vote` lets the IntegrityError through as a **500**. The grid then shows a save failure. **The fix:** - make `upsert_vote` race-safe with a Postgres `INSERT … ON CONFLICT (slot_id, user_id) DO UPDATE`, or catch the IntegrityError and retry as an update; - a test with two concurrent upserts, both succeeding with the last write winning; - optionally, the grid ignores a second press while one is saving. Lane 4's code (#730).

claude-bot referenced this issue

2026-09-26 15:33:22 +00:00

Lane 7: Talking — discussions, Talk tabs, Needs you, and Table rules & safety pages (#733) [HOLD for owner's T-answers] #846

rbrooks referenced this issue from a commit

2026-09-26 15:45:17 +00:00

fix(webapp): race-safe vote upsert, and start/commit-timing evidence (#844, #845)

claude-bot referenced this issue from a pull request that will close it,

2026-09-26 15:45:45 +00:00

fix(webapp): two quick votes on the same slot no longer race into a 500 (#844) #847

claude-bot closed this issue

2026-09-26 16:58:03 +00:00

claude-bot referenced this issue from a commit

2026-09-26 16:58:05 +00:00

Merge PR #847: two quick votes on the same slot no longer race into a 500 (#844)

claude-bot commented

2026-09-26 16:58:38 +00:00

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Fixed by #847, merged 2026-09-26.

The fix: upsert_vote is now a single INSERT … ON CONFLICT ON CONSTRAINT uq_votes_slot_user DO UPDATE, so the second writer updates the first one's row.

The test: a concurrency test drives two real sessions over separate connections, and both succeed. Before the fix it failed with the exact IntegrityError.

The optional frontend guard (ignoring a second press while a save is in flight) wasn't needed, since the server is now race-safe.

Fixed by #847, merged 2026-09-26. **The fix:** `upsert_vote` is now a single `INSERT … ON CONFLICT ON CONSTRAINT uq_votes_slot_user DO UPDATE`, so the second writer updates the first one's row. **The test:** a concurrency test drives two real sessions over separate connections, and both succeed. Before the fix it failed with the exact IntegrityError. The optional frontend guard (ignoring a second press while a save is in flight) wasn't needed, since the server is now race-safe.

claude-bot referenced this issue

2026-09-26 18:16:23 +00:00

Routes answer 200 before their commit: get_db commits after the response is sent #851