PostgreSQL version:

superuser_reserved_connections

Determines the number of connection slots that are reserved for connections by PostgreSQL superusers. At most max_connections connections can ever be active simultaneously. Whenever the number of active concurrent connections is at least max_connections minus superuser_reserved_connections, new connections will be accepted only for superusers, and no new replication connections will be accepted.

The default value is three connections. The value must be less than max_connections minus max_wal_senders. This parameter can only be set at server start.

Recommendations

You should have at least one superuser connection open for troubleshooting at all times. So if you run more than two concurrent regular administrative tasks, you'll need more reserved connections. Note that this number is taken from max_connections, not in addition to it.

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