PostgresqlReplicationBehind

PostgresqlReplicationBehind #

“Replication lag is greater than 60 seconds on server {{$labels.instance}}. Currently {{ $value }} seconds behind”

Alert Rule
alert: PostgresqlReplicationBehind
annotations:
  description: |-
    "Replication lag is greater than 60 seconds on server {{$labels.instance}}.  Currently {{ $value }} seconds behind"
      VALUE = {{ $value }}
      LABELS = {{ $labels }}    
  runbook: https://srerun.github.io/prometheus-alerts/runbooks/postgres-exporter/postgresqlreplicationbehind/
  summary: Postgresql replication is more than 60s behind
expr: pg_replication_lag_seconds > 60
for: 5m
labels:
  severity: warning

Here is a runbook for the Prometheus alert rule:

Meaning #

The PostgresqlReplicationBehind alert is triggered when the replication lag of a PostgreSQL server exceeds 60 seconds. This means that the standby server is not keeping up with the primary server, and data may not be properly replicated.

Impact #

If left unresolved, this issue can lead to:

  • Data inconsistencies between the primary and standby servers
  • Increased risk of data loss in the event of a failover
  • Performance degradation due to increased load on the primary server
  • Potential for prolonged downtime during failover or maintenance

Diagnosis #

To diagnose the issue, follow these steps:

  1. Check the PostgreSQL server logs for any errors or warnings related to replication
  2. Verify that the standby server is properly configured and running
  3. Check the network connection between the primary and standby servers for any issues
  4. Verify that the replication lag is not caused by a slow network connection
  5. Check the PostgreSQL server metrics (e.g. pg_stat_replication) to determine the cause of the replication lag

Mitigation #

To mitigate the issue, follow these steps:

  1. Investigate and resolve any underlying issues causing the replication lag
  2. Adjust the PostgreSQL configuration to optimize replication performance (e.g. increasing the wal_sender_timeout parameter)
  3. Consider increasing the resources (e.g. CPU, memory) of the standby server to improve replication performance
  4. Implement additional monitoring and alerting to detect replication issues earlier
  5. Perform a failover to the standby server to ensure data consistency and availability

For more detailed instructions and troubleshooting steps, please refer to the PostgresqlReplicationBehind runbook.

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