Thanks for the replies. I'm running Postgres 8.2 on Windows XP, Intel Core Duo (though Postgres seems to use only one 1 core).
The queries are self joins on very large tables, with lots of nested loops.
On Mon, Jul 27, 2009 at 9:40 PM, Tom Lane
<tgl@sss.pgh.pa.us> wrote:
Chris <
dmagick@gmail.com> writes:
> Robert James wrote:
>> Hi. I'm seeing some weird behavior in Postgres. I'm running read only
>> queries (SELECT that is - no UPDATE or DELETE or INSERT is happening at
>> all). I can run one rather complicated query and the results come
>> back... eventually. Likewise with another. But, when I run both
>> queries at the same time, Postgres seems to ground to a halt.
> They're probably not blocking each other but more likely you're
> exhausting your servers resources. If they return "eventually"
> individually, then running both at the same time will take at least
> "eventually x2".
It could be a lot more than x2. If the two queries together eat enough
RAM to drive the machine into swapping, where it didn't swap while
doing one at a time, the slowdown could be orders of magnitude.
Watching vmstat output might be informative --- it would at least give
an idea if the bottleneck is CPU, I/O, or swap.
regards, tom lane