Code Room
On-callHardoc-g238
Subject Database incidentsLevel Senior–Staff~40 minCommon in Databases & SQL · Storage & CDN · Reliability & on-call · Distributed systems interviewsIndustries Technology, Software development

Question

Postgres primary. Disk usage on the data volume climbed steadily over 2 days and just hit 100%; the DB is now refusing writes / crashing on `could not write to file ... No space left on device`. The `pg_wal` directory is huge. There was no traffic spike. Two weeks ago a team set up a logical-replication subscriber for a new data pipeline; that subscriber has been down for days. Triage, get writes back safely, and prevent recurrence.

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.

Diagram & narrate the incident
Loading whiteboard…
Run or narrate your approach, then ask the coach.