Re: Monitoring number of backends

On Tue, Oct 22, 2013 at 12:41:58PM -0500, andy wrote:
- Hi all.
-
- My website is about to get a little more popular.  I'm trying to add in
- some measurements to determine an upper limit of how many concurrent
- database connections I'm currently using.
-
- I've started running this:
-
- SELECT sum(numbackends) AS count, sum(xact_commit) as ttlcommit FROM
- pg_stat_database;
-
- Every 10 seconds or so.  I don't think its what I want though.  It seems
- way too small.  I'm guessing that its not a measure of the previous 10
- seconds.  Its a count of how many backends are in use at the exact
- moment I run the sql.
-
- Is there a cumulative count someplace?
-
- Thanks for your time,
-
- -Andy

You've gotten good info from the other guys on how to scale your're DB
but to answer you're original question. I usually use this query:

select count(*) from pg_stat_activity where state <> 'idle';

That gives you the # of "active" connections to your database and is
something you want to try to get good metrics on.

Idle connections have some overhead but if Active > # of CPUs your performance
starts to degrade. Now, really that's pretty normal but, ideally, you need to
know what the ratio of Active Connections to # CPUs still gives you acceptable
performance. And that's really based on your app and hardware.