On-callHardoc-g019

Subject Disk fullLevel Senior–Staff~35 minCommon in Databases & SQL · Storage & CDN · Distributed systems interviewsIndustries Technology, Software development

Question

At 01:10 your Postgres primary stops accepting writes: the app logs 'could not extend file ... No space left on device' and the database goes effectively read-only. df shows the data volume at 100%. The pg_wal directory has ballooned to hundreds of GB. You recently set up a new logical replication subscriber for an analytics pipeline, and that subscriber has been down for maintenance since yesterday afternoon. How do you triage, recover service, 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.

Learn the concepts

Diagram & narrate the incident

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Run or narrate your approach, then ask the coach.