Parameter · Connections and Authentication / Connection Settings
reserved_connections
Sets the number of connection slots reserved for roles with privileges of pg_use_reserved_connections.
- Default:
0 - Type: integer
- Range: 0 … 262143
- Applies: Restart required
In plain words
Extra connection slots kept for trusted roles that are not superusers, such as a monitoring agent. Grant them pg_use_reserved_connections and they can still connect when the application has exhausted its share.
The default 0 turns this reserve off.
For DBAs and operators
Added in PostgreSQL 16. When the number of free slots is greater than superuser_reserved_connections but ≤ superuser_reserved_connections + reserved_connections, only superusers and members of pg_use_reserved_connections are admitted. Others get FATAL: remaining connection slots are reserved for roles with privileges of the "pg_use_reserved_connections" role. Once only the superuser reserve is left, even these roles get the SUPERUSER message.
GRANT pg_use_reserved_connections TO monitoring;
-- postgresql.conf (restart required)
reserved_connections = 2The value must be less than max_connections − superuser_reserved_connections, and it reduces the number of slots ordinary roles can use. Reserve slots for operational roles that genuinely need to connect during a connection storm, while leaving the superuser reserve available for emergency administration. Access to these slots is determined by membership in pg_use_reserved_connections; the right count depends on your monitoring, automation and incident-response connection needs.
How to change it
Change in postgresql.conf or ALTER SYSTEM, then restart the server.
See it in context
Roles and privileges Client backend Process model Postmaster