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 <t...@sss.pgh.pa.us> wrote: > Chris <dmag...@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 >
