PostgresqlDeadLocks

PostgresqlDeadLocks #

PostgreSQL has dead-locks

Alert Rule
alert: PostgresqlDeadLocks
annotations:
  description: |-
    PostgreSQL has dead-locks
      VALUE = {{ $value }}
      LABELS = {{ $labels }}    
  runbook: https://srerun.github.io/prometheus-alerts/runbooks/postgres-exporter/postgresqldeadlocks/
  summary: Postgresql dead locks (instance {{ $labels.instance }})
expr: increase(pg_stat_database_deadlocks{datname!~"template.*|postgres"}[1m]) > 5
for: 0m
labels:
  severity: warning

Meaning #

The PostgresqlDeadLocks alert is triggered when the number of deadlocks in a PostgreSQL database exceeds 5 within a 1-minute window. Deadlocks occur when two or more transactions are blocked, each waiting for the other to release a resource. This can lead to performance degradation, slow query execution, and even crashes.

Impact #

  • Performance degradation: Deadlocks can cause queries to take longer to execute, leading to increased latency and decreased throughput.
  • Unavailability: In extreme cases, deadlocks can cause PostgreSQL to become unresponsive or even crash, leading to downtime and data loss.
  • Data Inconsistency: Deadlocks can also lead to inconsistent data, as transactions may be rolled back or terminated unexpectedly.

Diagnosis #

To diagnose the root cause of the deadlocks:

  1. Check the PostgreSQL logs for error messages related to deadlocks.
  2. Use the pg_stat_activity view to identify the queries and transactions involved in the deadlock.
  3. Analyze the database schema and query patterns to identify potential bottlenecks and hotspots.
  4. Check for any ongoing maintenance operations, such as vacuuming or indexing, that may be contributing to the deadlocks.

Mitigation #

To mitigate the deadlocks:

  1. Immediate Response: Cancel any blocked queries and restart the affected transactions.
  2. Short-Term Fix: Adjust the max_locks_per_transaction setting to increase the number of locks available to transactions.
  3. Long-Term Solution:
    • Implement row-level locking instead of table-level locking.
    • Optimize database schema and query patterns to reduce contention and hotspots.
    • Increase the deadlock_timeout setting to allow transactions to wait longer before aborting.
  4. Monitoring and Prevention: Continuously monitor PostgreSQL performance and query activity to identify potential deadlock situations before they occur.
  5. Post-Incident Analysis: Perform a post-mortem analysis to identify the root cause of the deadlock and implement changes to prevent similar situations in the future.
Edit this page