Use the Replication Slot Retained WAL alert in Mini DBA to monitor PostgreSQL instances and make this condition visible before it becomes a wider database incident.
Mini DBA describes this alert as: Replication slots retaining too much WAL can fill the WAL volume when consumers lag or disappear. The default evaluation frequency is Minute, so the alert is intended to be close enough to operational reality for live triage.
This alert protects storage and recovery capacity. It helps you find growth, retention, and backup conditions that can stop writes, break recovery objectives, or leave the server without enough working space for normal database activity.
Enable it where replication, read replicas, failover, or reporting copies are part of the service design. Disable it on standalone systems that do not use replication so the alert list stays focused.
Threshold meaning: GB retained. Major threshold: 50 GB. Minor threshold: 10 GB. Comparison direction: "over". Use higher thresholds on batch-heavy, development, or intentionally bursty systems where brief pressure is expected. Use lower thresholds on latency-sensitive production systems, small instances with little headroom, and services with strict recovery or availability commitments.
Free space by removing safe-to-delete files, expanding the volume or tablespace, moving growth-heavy objects, correcting retention settings, or shrinking only after a documented one-off event. For recovery-related areas, verify that backups and log shipping or archiving are healthy before deleting anything.
If this alert is noisy, check whether the workload naturally has short bursts. Raise the duration or threshold for expected batch windows, but keep a lower route for production systems where user-facing latency matters. Avoid simply disabling the alert until you know whether the noise is caused by threshold choice or by a real capacity trend.