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Re: How much RAM is too much ?

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: <pgsql-admin(at)postgresql(dot)org>,"A J" <s5aly(at)yahoo(dot)com>
Subject: Re: How much RAM is too much ?
Date: 2010-07-22 20:55:29
Message-ID: 4C4869F10200002500033B8C@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-admin
A J <s5aly(at)yahoo(dot)com> wrote:
 
> Cost aside, are there any technical factors to consider before
> increasing RAM (assuming the system can support it) ? Is there a
> sweet spot beyond which more RAM does not help Postgres or
> actually harms ?
 
I've never heard of putting more RAM in a machine hurting
performance, as long as it's the right type of RAM for that machine.
On the other hand, you can easily configure PostgreSQL to allocate
more RAM for specific purposes than is good.
 
> If my database is only couple of hundred Gigs, can I not just have
> RAM that big and have read from buffer all the time ?
 
Sure, as long as you allow enough extra for the OS and all other
processes.  If you're looking at hundreds of GB of RAM on a box,
plan on letting the OS use the vast majority of that for caching.
 
This doesn't obviate the need for a RAID controller with its own BBU
RAM if you want write performance to be good.
 
-Kevin

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