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Re: Tuning for mid-size server

From: Ron Johnson <ron(dot)l(dot)johnson(at)cox(dot)net>
To: PgSQL Performance ML <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Tuning for mid-size server
Date: 2003-10-22 21:36:51
Message-ID: 1066858611.12532.223.camel@haggis (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On Tue, 2003-10-21 at 14:27, Christopher Browne wrote:
> In the last exciting episode, josh(at)agliodbs(dot)com (Josh Berkus) wrote:
> > So what is the ceiling on 32-bit processors for RAM? Most of the
> > 64-bit vendors are pushing Athalon64 and G5 as "breaking the 4GB
> > barrier", and even I can do the math on 2^32.  All these 64-bit
> > vendors, then, are talking about the limit on ram *per application*
> > and not per machine?
> I have been seeing ia-32 servers with 8GB of RAM; it looks as though
> there are ways of having them support ("physically, in theory, if you
> could get a suitable motherboard") as much as 64GB.
> But that certainly doesn't get you past 2^32 bytes per process, and
> possibly not past 2^31 bytes/process.
> >From Linux kernel help:
>     Linux can use up to 64 Gigabytes of physical memory on x86
>     systems.  However, the address space of 32-bit x86 processors is
>     only 4 Gigabytes large. That means that, if you have a large
>     amount of physical memory, not all of it can be "permanently
>     mapped" by the kernel. The physical memory that's not permanently
>     mapped is called "high memory".
> And that leaves open the question of how much shared memory you can
> address.  That presumably has to fit into the 4GB, and if your
> PostgreSQL processes had (by some fluke) 4GB of shared memory, there
> wouldn't be any "local" memory for sort memory and the likes.
> Add to that the consideration that there are reports of Linux "falling
> over" when you get to right around 2GB/4GB.  I ran a torture test a
> while back that _looked_ like it was running into that; I can't verify
> that, unfortunately.

Well thank goodness that Linux & Postgres work so well on Alpha
and long-mode AMD64.

Ron Johnson, Jr. ron(dot)l(dot)johnson(at)cox(dot)net
Jefferson, LA USA

"Fear the Penguin!!" 

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