On-callMediumoc-g125

Subject Data corruptionLevel Mid–Senior~30 minCommon in Databases & SQL interviewsIndustries Technology, Software development

Question

Support reports user names and addresses with accented and non-Latin characters now show as garbled mojibake (e.g. 'José' → 'JosÃ©', '北京' → question marks) for records created in the last 3 hours. Older records are fine. Dashboards: error rate normal, no failed inserts. Context: a service was redeployed 3 hours ago after a connection-library upgrade; the MySQL columns are `utf8mb4`, but the new driver's default connection charset is `latin1` (the old driver defaulted to `utf8mb4`). How do you triage, stop further corruption, and recover the already-corrupted rows?

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.