How to diagnose and fix the 8004 sqlserver_rejected_establishment_of_sqlconnection error code in Postgres.

The 08004 error code in PostgreSQL represents “sqlserver_rejected_establishment_of_sqlconnection”. This error occurs when the server rejects the establishment of a SQL connection for some reason. Here are some steps to diagnose and fix this issue:

  1. Review Server Logs:
  • The first step should always be to check the PostgreSQL server logs for detailed error messages that explain why the connection was rejected.
  1. Examine pg_hba.conf Configuration:
  • Incorrect settings in the pg_hba.conf file can lead to the server rejecting connections. Make sure that the client’s IP address, the database they’re connecting to, and the user role have the correct permissions and are using the appropriate authentication method.
  1. Check postgresql.conf Settings:
  • In the postgresql.conf file, ensure that the listen_addresses parameter is correctly configured to accept connections on the desired interfaces.
  1. Validate User Credentials and Permissions:
  • Verify that the username and password are correct and that the user has permission to connect to the specified database.
  1. Database Role Attributes:
  • Check the role attributes for the user trying to connect using the psql command \du. Ensure the role has login permission and is not expired or locked.
  1. Check for Connection Limits:
  • The server might reject new connections if it has reached its maximum number of allowed connections. Check if increasing max_connections in postgresql.conf or using connection pooling can help.
  1. Network Restrictions:
  • Ensure that network firewalls, security groups, or other network policies are not blocking the connection to the PostgreSQL server’s port (default is 5432).
  1. SSL/TLS Configuration:
  • If the server is configured to require SSL connections, ensure that the client is configured to use SSL and that all necessary certificates are valid and properly located.
  1. Server Resource Exhaustion:
  • The server might reject connections if it’s running low on system resources like memory or CPU. Monitor the server’s resource usage and upgrade or scale as necessary.
  1. Authentication Method Mismatch:
    • The server could reject connections if the client is attempting to use an authentication method not supported for that user or database in the pg_hba.conf file.

For a more in-depth understanding of PostgreSQL error codes and their meanings, the PostgreSQL documentation is an excellent resource. If you encounter a situation that isn’t resolved by the standard troubleshooting steps, searching through community discussions, such as those on Stack Overflow, can also provide tailored solutions and advice from experienced PostgreSQL users.

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