Psql: error: connection to server on socket “/var/run/postgresql/.s.pgsql.5432” failed: fatal: sorry, too many clients already

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Answer:

This error can occur when the maximum number of clients that can connect to the PostgreSQL server has been reached. The server has a limit on the maximum number of concurrent connections it can handle. When this limit is reached, new connections are refused, resulting in the “too many clients already” error.

To resolve this error, you can try one or more of the following steps:

  1. Check existing connections: Use the following query to check the current number of connections:

    SELECT count(*) FROM pg_stat_activity;

    This will give you the count of active connections to the PostgreSQL server. If it is close to or exceeds the maximum number of allowed connections, you might need to terminate some existing connections.

  2. Increasing maximum connections: If your application consistently requires a high number of connections, you can increase the maximum number of connections allowed by modifying the PostgreSQL server configuration. The configuration file is typically located at /etc/postgresql/{version}/main/postgresql.conf. Look for the max_connections parameter and increase its value. After modifying the configuration, you need to restart the PostgreSQL server for the changes to take effect.
  3. Optimizing connection handling: Analyze your application’s connection usage patterns and see if there are any areas where connection pooling or connection reuse can be implemented to reduce the number of connections required.
  4. Scaling resources: If none of the above solutions resolve the issue, you might need to consider scaling your PostgreSQL infrastructure by adding more resources such as additional servers or upgrading to a higher-capacity server.

It’s important to note that increasing the maximum number of connections should be done cautiously, as it consumes additional system resources. Monitoring your server’s performance and considering the available system resources is crucial when making changes.

Example on how to check and terminate existing connections using psql command-line tool: 


   psql -U postgres -c "SELECT pg_terminate_backend(pg_stat_activity.pid) FROM pg_stat_activity WHERE pg_stat_activity.datname = 'your_database_name' AND pid <> pg_backend_pid();"

In the above command, replace postgres with the username of your PostgreSQL database and your_database_name with the name of the database for which you want to terminate connections.

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