Check out techdocs.postgresql.org and download PL/Sh by Peter Eisentraut. You
can do the job with the help of an embedded Shell script.
As far as I know there is no other (easy way) of retrieving that information.
Try something like that:
CREATE OR REPLACE FUNCTION "backends_number"() RETURNS "text" AS '
#!/bin/sh
expr $(ps ax | egrep -e ''postgres:.*local'' | wc -l) - 1
' LANGUAGE 'plsh';
I have not tested this extensively but it should work.
Note: PL/Sh is not a trusted embedded languages (system calls are allowed) ->
use a separate database for that and don't use your production database
(security!!!!).
Hans
