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Re: [PERFORMANCE] Buying hardware

From: david(at)lang(dot)hm
To: David Rees <drees76(at)gmail(dot)com>
Cc: Jeff <threshar(at)threshar(dot)is-a-geek(dot)com>, Matthew Wakeling <matthew(at)flymine(dot)org>, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>, A B <gentosaker(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: [PERFORMANCE] Buying hardware
Date: 2009-01-27 04:06:09
Message-ID: alpine.DEB.1.10.0901262001390.16162@asgard.lang.hm (view raw or flat)
Thread:
Lists: pgsql-performance
On Mon, 26 Jan 2009, David Rees wrote:

> And yes, the more memory you can squeeze into the machine, the better,
> though you'll find that after a certain point, price starts going up
> steeply.  Of course, if you only have a 15GB database, once you reach
> 16GB of memory you've pretty much hit the point of diminishing
> returns.

actually, you need more memory than that. besides the data itself you 
would want memory for several other things, among them:

1. your OS
2. your indexes
3. you per-request memory allocations (for sorting, etc)
   this is highly dependant on your workload (type and number of parallel 
requests)
4. 'dead' tuples in your table (that will be cleared by a vaccum, but 
haven't been yet)

and probably other things as well.

I don't know how large a database will fit in 16G of ram, but I suspect 
it's closer to 8G than 15G.

any experts want to throw out a rule-of-thumb here?

David Lang

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