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Re: Hardware suggestions for Linux/PGSQL server

From: William Yu <wyu(at)talisys(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Hardware suggestions for Linux/PGSQL server
Date: 2003-12-11 23:32:47
Message-ID: brauqp$1p4g$1@news.hub.org (view raw or flat)
Thread:
Lists: pgsql-performance
Jeff Bohmer wrote:
> It seems I don't fully understand the bigmem situation.  I've searched 
> the archives, googled, checked RedHat's docs, etc.  But I'm getting 
> conflicting, incomplete and/or out of date information.  Does anyone 
> have pointers to bigmem info or configuration for the 2.4 kernel?

Bigmem is the name for Linux's PAE support.

> If Linux is setup with 2GB for kernel and 2GB for user, would that be OK 
> with a DB size of 2-2.5 GB?  I'm figuring the kernel will cache most/all 
> of the DB in it's 2GB and there's 2GB left for PG processes. Where does 
> PG's SHM buffers live, kernel or user?  (I don't plan on going crazy 
> with buffers, but will guess we'd need about 128MB, 256MB at most.)

PG's SHM buffers live in user. Whether Linux's OS caches lives in user 
or kernel, I think it's in kernel and I remember reading a max of ~950KB 
w/o bigmem which means your 3.5GB of available OS memory will definitely 
have to be swapped in and out of kernel space using PAE.

>> Well if this is the case, you probably should get an Opteron server 
>> *now* and just run 32-bit Linux on it until you're sure about the 
>> software. No point in buying a Xeon and then throwing the machine away 
>> in a year when you decide you need 64-bit for more speed.
> 
> That's a good point.  I had forgotten about the option to run 32bit on 
> an Operton.  If we had 3GB or 4GB initially on an Opteron, we'd need 
> bigmem for 32bit Linux, right?
> 
> This might work nicely since we'd factor in the penalty from PAE for now 
> and have the performance boost from moving to 64bit available on 
> demand.  Not having to build another DB server in a year would also be 
> nice.
> 
> FYI, we need stability first and performance second.

We ordered a 2x Opteron server the moment the CPU was released and it's 
been perfect -- except for one incident where the PCI riser card had 
drifted out of the PCI slot due to the heavy SCSI cables connected to 
the card.

I think most of the Opteron server MBs are pretty solid but you want 
extra peace-of-mind, you could get a server from Newisys as they pack in 
a cartload of extra monitoring features.


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Subject: Measuring execution time for sql called from PL/pgSQL
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