PostgresDB 40P01: Deadlock detected

Raised when a deadlock situation is detected within a transaction.
  1. Identify the query causing the deadlock:
    • Run SELECT * FROM pg_stat_activity WHERE state = 'active'; to see active queries that might be involved in the deadlock.
  2. Check the PostgreSQL logs:
    • Locate and review the PostgreSQL log files (typically found in the pg_log directory within the data directory) for detailed error messages and the queries involved in the deadlock.
  3. Obtain lock information:
    • Execute SELECT relation::regclass, * FROM pg_locks WHERE NOT GRANTED; to see which queries are waiting for locks, which can help identify the sources of the deadlock.
  4. Cancel or terminate the offending query:
    • Use SELECT pg_cancel_backend(pid); to gently cancel a query using its PID, or
    • SELECT pg_terminate_backend(pid); to forcefully terminate the backend process if canceling doesn't work. Replace pid with the process ID of the query involved in the deadlock.
  5. Analyze and optimize the queries:
    • After resolving the immediate deadlock, consider analyzing the queries and transaction patterns that contributed to the deadlock. Use EXPLAIN or EXPLAIN ANALYZE with the queries to understand their execution plans and identify potential optimizations.

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