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max_connections / shared_buffers / effective_cache_size questions

From: Puddle <rotaecho(at)yahoo(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: max_connections / shared_buffers / effective_cache_size questions
Date: 2005-06-24 18:54:31
Message-ID: 20050624185431.56684.qmail@web32807.mail.mud.yahoo.com (view raw or flat)
Thread:
Lists: pgsql-performance
Hello, I'm a Sun Solaris sys admin for a start-up
company.  I've got the UNIX background, but now I'm
having to learn PostgreSQL to support it on our
servers :)

Server Background:

Solaris 10 x86
PostgreSQL 8.0.3 
Dell PowerEdge 2650 w/4gb ram.
This is running JBoss/Apache as well (I KNOW the bad
juju of running it all on one box, but it's all we
have currently for this project). I'm dedicating 1gb
for PostgreSQL alone.

So, far I LOVE it compared to MySQL it's solid.

The only things I'm kind of confused about (and I've
been searching for answers on lot of good perf docs,
but not too clear to me) are the following:

1.) shared_buffers I see lot of reference to making
this the size of available ram (for the DB).  However,
I also read to make it the size of pgdata directory.  

I notice when I load postgres each daemon is using the
amount of shared memory (shared_buffers).  Our current
dataset (pgdata) is 85mb in size.  So, I'm curious
should this size reflect the pgdata or the 'actual'
memory given?

I currently have this at 128mb 

2.) effective_cache_size - from what I read this is
the 'total' allowed memory for postgresql to use
correct? So, if I am willing to allow 1GB of memory
should I make this 1GB?

3.) max_connections, been trying to figure 'how' to
determine this #.  I've read this is buffer_size+500k
per a connection.  

ie.  128mb(buffer) + 500kb = 128.5mb per connection?

I was curious about 'sort_mem' I can't find reference
of it in the 8.0.3 documentation, has it been removed?

work_mem and max_stack_depth set to 4096
maintenance_work_mem set to 64mb

Thanks for any help on this.  I'm sure bombardment of
newbies gets old :)

-William


		
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