Re: Postgre Eating Up Too Much RAM

On our old server, our hosting company said the server was running out of
RAM and then became unresponsive. I haven't checked about the new server
yet.

I noticed our problems started about the time when we loaded a new client
into the database that had nearly 1 GB of large files stored in BLOBs -
PDFs, images, Word docs, etc. We have a daily process that pulls these
large files out for search indexing. It is likely the new server crashed
at about the time this indexing was taking place.

When we are reading large files out of the BLOBs (upwards of 100 MB a
piece), could that cause Postgres to eat up the RAM that remains? With a
server having 32 GB RAM I would think only two database connections (that
should be all that the processes use for the indexing) would NOT have this
effect.

I am glad to see I am not totally missing something obvious but am also a
bit flummoxed over this issue. With this server upgrade I changed OS
(CentOS to Ubuntu), upgraded Postgres (8.3 to 8.4), increased the RAM (6 GB
to 32 GB), increased the hard drive space (1/2 TB to over 1.5 TB on a RAID
10), changed to completely new hardware, removed a ton of stuff on the
server we didn't need (like CPanel and its baggage) and even had our daily
backups turned off temporarily. In fact, the old server was lasting 2 days
or more before having problems and with the new server it went belly up in
just a day.

Is there any kind of diagnostics you can think of that would help get to
the root of the problem - something I could put in a cron job or a monitor
app I could run on the server that would at least tell us what is going on
if / when it happens again?

Thanks for all the help!
Aaron

==================================================================
Aaron Bono
Aranya Software Technologies, Inc.
http://www.aranya.com
http://codeelixir.com
==================================================================

On Tue, Nov 13, 2012 at 9:19 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Craig Ringer <craig(at)2ndQuadrant(dot)com> writes:
> > On 11/14/2012 06:12 AM, Aaron Bono wrote:
> >> Am I reading this right? Are there individual connections using over
> >> 300 MB or RAM by themselves?
>
> > If I recall correctly, RSS is charged against a PostgreSQL back-end when
> > it touches `shared_buffers`. So that doesn't necessarily mean that the
> > back-end is using the full amount of memory listed as RSS.
>
> Yeah. Since Aaron's got shared_buffers set to 256MB, the shared memory
> segment is something more than that (maybe 270-280MB, hard to be sure
> without checking). The RSS numbers probably count all or nearly all of
> that for each process, but of course there's really only one copy of the
> shared memory segment. RSS is likely double-counting the postgres
> executable as well, which means that the actual additional memory used
> per process is probably just a few meg, which is in line with most
> folks' experience with PG.
>
> The "free" stats didn't look like a machine under any sort of memory
> pressure --- there's zero swap usage, and nearly half of real RAM is
> being used for disk cache, which means the kernel can find no better
> use for it than caching copies of disk files. Plus there's still 10G
> that's totally free. Maybe things get worse when the machine's been up
> longer, but this sure isn't evidence of trouble.
>
> I'm inclined to think that the problem is not RAM consumption at all but
> something else. What exactly happens when the server "hangs"?
>
> regards, tom lane
>
>
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