Query a parameter (postgresql.conf setting) like "max_connections"

Does anyone know if it's even possible (and how, if yes) to query a database server setting in PostgreSQL (9.1)?

I need to check the max_connections (maximum number of open db connections) setting.

You can use SHOW:

SHOW max_connections;

This returns the currently effective setting. Be aware that it can differ from the setting in postgresql.conf as there are a multiple ways to set run-time parameters in PostgreSQL. To reset the "original" setting from postgresql.conf in your current session:

RESET max_connections;

However, not applicable to this particular setting. The manual:

> This parameter can only be set at server start.

To see all settings:

SHOW ALL;

There is also pg_settings:

> The view pg_settings provides access to run-time parameters of the > server. It is essentially an alternative interface to the SHOW and > SET commands. It also provides access to some facts about each > parameter that are not directly available from SHOW, such as minimum > and maximum values.

For your original request:

SELECT *
FROM   pg_settings
WHERE  name = 'max_connections';

Finally, there is current_setting(), which can be nested in DML statements:

SELECT current_setting('max_connections');

Related:

• https://stackoverflow.com/questions/30179441/how-to-test-my-ad-hoc-sql-with-parameters-in-postgres-query-window/30179814#30179814