Date: Mon, 24 Oct 2005 16:14:20 +1300
From: Mark Kirkwood <markir@paradise.net.nz>
Subject: Re: Used Memory
In-reply-to: <02b501c5d83c$d6bf0f10$1e21100a@ghwk02002147>
To: "Christian Paul B. Cosinas" <cpc@cybees.com>
Cc: pgsql-performance@postgresql.org
Message-id: <435C518C.8070505@paradise.net.nz>
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References: <02b501c5d83c$d6bf0f10$1e21100a@ghwk02002147>

Christian Paul B. Cosinas wrote:
>  
> 
> Here is the result of “free” command” I am talking about.
> 
> What does this result mean?
> 

I seem to recall the Linux man page for 'free' being most 
unenlightening, so have a look at:

http://gentoo-wiki.com/FAQ_Linux_Memory_Management

(For Gentoo, but should be applicable to RHEL).

The basic idea is that modern operating systems try to make as much use 
of the memory as possible. Postgresql depends on this behavior - e.g. a 
page that has previously been fetched from disk, will be cached, so it 
can be read from memory next time, as this is faster(!)

>  
> 
> I just noticed that as long as the free memory in the first row (which 
> is 55036 as of now) became low, the slower is the response of the 
> database server.
>  

Well, you could be swapping - what does the swap line of 'free' show then?

Also, how about posting your postgresql.conf (or just the non-default 
parameters) to this list?

Some other stuff that could be relevant:

- Is the machine just a database server, or does it run (say) Apache + Php?
- When the slowdown is noticed, does this coincide with certain 
activities - e.g, backup , daily maintenance, data load(!) etc.


regards

Mark

> 
> I choose Polesoft Lockspam to fight spam, and you?
> http://www.polesoft.com/refer.html

Nope, not me either.