On Wed, 12 Feb 2003, Tatsuo Ishii wrote:
> > My other pet peeve is the default max connections setting. This should be
> > higher if possible, but of course, there's always the possibility of
> > running out of file descriptors.
> >
> > Apache has a default max children of 150, and if using PHP or another
> > language that runs as an apache module, it is quite possible to use up all
> > the pgsql backend slots before using up all the apache child slots.
> >
> > Is setting the max connections to something like 200 reasonable, or likely
> > to cause too many problems?
>
> It likely. First you will ran out kernel file descriptors. This could
> be solved by increasing the kernel table or lowering
> max_files_per_process, though. Second the total throughput will
> rapidly descrease if you don't have enough RAM and many
> CPUs. PostgreSQL can not handle many concurrent
> connections/transactions effectively. I recommend to employ some kind
> of connection pooling software and lower the max connections.
Don't know if you saw my other message, but increasing max connects to 200
used about 10% of all my semaphores and about 10% of my file handles.
That was while running pgbench to create 200 simo sessions.
Keep in mind, on my fairly small intranet database server, I routinely
have >32 connections, most coming from outside my webserver. Probably no
more than 4 or 5 connects at a time come from there. These are all things
like Windows boxes with ODBC running access or something similar. Many of
the connections are idle 98% of the time, and use little or no real
resources, even getting swapped out should the server need the spare
memory (it doesn't :-) that machine is set to 120 max simos if I remember
correctly.
while 200 may seem high, 32 definitely seems low. So, what IS a good
compromise? for this and ALL the other settings that should probably be a
bit higher. I'm guessing sort_mem or 4 or 8 meg hits the knee for most
folks, and the max fsm settings tom has suggested make sense.
What wal_sync method should we make default? Or should we pick one based
on the OS the user is running?
