Dashboard query plan regression
A dashboard query slowed from 200ms to 8s for some users but stayed fast for others, with no deploy. The query filters tasks by `assignee_id` and `status`. `EXPLAIN ANALYZE` on a slow case shows the planner estimating ~50 rows but actually returning ~900k — it chose an index nested loop that's terrible at that real volume. The `status` column is wildly skewed: 95% of all rows are `status='done'`, and the slow users are ones querying their large pile of done tasks. Stats are up to date. Triage and mitigate.
What a strong answer looks like
Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.
0:00 of about 30 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.