On-callMediumoc-g064

Subject Bad rolloutLevel Mid–Senior~30 minCommon in Databases & SQL interviewsIndustries Software development

Question

v62 of the dashboard service (Ruby on Rails) rolls out at 11:30. Page loads on the project-list view get slow (p95 from 300ms to 4s) and the primary database's query rate jumps 8x while its CPU climbs to 95%, even though user traffic is unchanged. Slow-query logs show a flood of tiny identical-shaped SELECTs against the 'members' table, one per project row. v62 'cleaned up' the project-list query by removing an explicit eager-load. 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.

Learn the concepts

Diagram & narrate the incident

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Run or narrate your approach, then ask the coach.