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Re: PostgreSQL 8.4 performance tuning questions

From: Greg Smith <gsmith(at)gregsmith(dot)com>
To: Rauan Maemirov <rauan(at)maemirov(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: PostgreSQL 8.4 performance tuning questions
Date: 2009-07-31 04:10:40
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On Thu, 30 Jul 2009, Rauan Maemirov wrote:

> maintenance_work_mem = 1GB
> work_mem = 192MB
> shared_buffers = 7680MB
> max_connections = 80
> My box is Nehalem 2xQuad 2.8 with RAM 32Gb

While it looks like you sorted out your issue downthread, I wanted to 
point out that your setting for work_mem could be dangerously high here 
and contribute to problems with running out memory or using swap.  If each 
of your 80 clients was doing a sort at the same time, you'd be using 80 * 
192MB + 7680MB = 15360GB of RAM just for the server.  The problem is that 
each client could do multiple sorts, so usage might even got higher. 
Unless you have a big data warehouse setup, more common work_mem settings 
are in the 16-64MB range rather than going this high.  Just something to 
keep an eye on if you find a lot of memory is being used by the database 
processes.  I really need to refine the pgtune model to more carefully 
account for this particular problem, it's a bit too aggressive here for 
people who aren't proactively watching the server's RAM after changing the 

* Greg Smith gsmith(at)gregsmith(dot)com Baltimore, MD

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Subject: Performance 8.4.0
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