Re: Potential memory usage issue

In response to David Brain <dbrain(at)bandwidth(dot)com>:
>
> I recently migrated one of our large (multi-hundred GB) dbs from an
> Intel 32bit platform (Dell 1650 - running 8.1.3) to a 64bit platform
> (Dell 1950 - running 8.1.5). However I am not seeing the performance
> gains I would expect

What were you expecting? It's possible that your expectations are
unreasonable.

In our testing, we found that 64bit on the same hardware as 32bit only
gave us a 5% gain, in the best case. In many cases the gain was near
0, and in some there was a small performance loss. These findings seemed
to jive with what others have been reporting.

> - I am suspecting that some of this is due to
> differences I am seeing in reported memory usage.
>
> On the 1650 - a 'typical' postmaster process looks like this in top:
>
> 5267 postgres 16 0 439m 427m 386m S 3.0 21.1 3:31.73 postmaster
>
> On the 1940 - a 'typical' postmaster process looks like:
>
> 10304 postgres 16 0 41896 13m 11m D 4 0.3 0:11.73 postmaster
>
> I currently have both systems running in parallel so the workloads will
> be approximately equal. The configurations of the two systems in terms
> of postgresql.conf is pretty much identical between the two systems, I
> did make some changes to logging, but nothing to buffers/shared memory
> config.
>
> I have never seen a postmaster process on the new system consume
> anywhere near as much RAM as the old system - I am wondering if there is
> something up with the shared memory config/usage that is causing my
> performance issues. Any thoughts as to where I should go from here?

Provide more information, for one thing. I'm assuming from the top output
that this is some version of Linux, but more details on that are liable
to elicit more helpful feedback.

We run everything on FreeBSD here, but I haven't seen any difference in
the way PostgreSQL uses memory on ia32 FreeBSD vs. amd64 FreeBSD. Without
more details on your setup, my only suggestion would be to double-verify
that your postgresql.conf settings are correct on the 64 bit system.

--
Bill Moran
Collaborative Fusion Inc.

wmoran(at)collaborativefusion(dot)com
Phone: 412-422-3463x4023

****************************************************************
IMPORTANT: This message contains confidential information and is
intended only for the individual named. If the reader of this
message is not an intended recipient (or the individual
responsible for the delivery of this message to an intended
recipient), please be advised that any re-use, dissemination,
distribution or copying of this message is prohibited. Please
notify the sender immediately by e-mail if you have received
this e-mail by mistake and delete this e-mail from your system.
E-mail transmission cannot be guaranteed to be secure or
error-free as information could be intercepted, corrupted, lost,
destroyed, arrive late or incomplete, or contain viruses. The
sender therefore does not accept liability for any errors or
omissions in the contents of this message, which arise as a
result of e-mail transmission.
****************************************************************