Re: compiling, performance of PostGreSQL 8.3 on 64-bit processors

On Thu, Jun 26, 2008 at 7:12 PM, Adam Rich <adam(dot)r(at)sbcglobal(dot)net> wrote:
>
>> 1. I have heard of problems arising from compiling PostGreSQL (8.3) on
>> 64-bit
>> processors. What sort of problems am I likely to encounter and how
>> should I fix
>> them? We are will run Linux Redhat 5 on a Dell PE2950 III Quad Core
>> Xeon E54
>> 2.33 GHz, and a Dell PE2950 III Quad Core Xeon L5335 2.0 GHz.
>>
>> 2. Are there performance problems running PostGreSQL 8.3 on a 64-bit
>> processor?

Should compile and run fine--I haven't heard of any problems with it,
and PG has run on 64-bit systems (SGI, Sun, Alpha) long before there
was x86_64.

> I have a few more questions on the 64-bit topic. Is there any benefit
> to running a 32-bit OS (rhel 5 in this case) on a server with more than
> 4 GB of memory? In other words, can the OS-level cache take advantage
> of more than 4 GB of memory?

With a 32-bit kernel and >4GB of memory, you will indeed get more
available to cache from the OS. It's generally not recommended to use
more than 8GB with a 32-bit kernel.

> Can a process (such as PG backend) use
> more than 4 GB of shared memory on a 32-bit OS?

No, and the practical limit is more like 2GB (or less).

>Or is the 4 GB memory
> point the place where you normally transition to a 64-bit OS?

In this day and age there's not too much of a reason to run in 32 bits
on a server capable of 64. If necessary, you can run 32-bit legacy
binaries under a 64-bit kernel, if you set up the libraries properly.

> For people with experience running postgresql on systems with 16+ GB
> of memory, what parameter settings have you found to be effective?
> (This would be a large database that's mostly read-only that we'd
> like to fit completely in memory)

Can't help with this one, sorry.

> Is it possible to backup (pg_dump) from a 32-bit OS to a 64-bit OS,
> or is a plain SQL dump necessary?

pg_dump output (which by default *is* plain SQL, though there are two
other formats) is compatible across architectures. Backups of the
on-disk database files are not.

-Doug