Re: How to cripple a postgres server

On Tue, 2002-05-28 at 14:24, Tom Lane wrote:
> Stephen Robert Norris <srn(at)commsecure(dot)com(dot)au> writes:
> > One big difference, though, is that with the vacuum problem, the CPU
> > used is almost all (99%) system time; loading up the db with lots of
> > queries increases user time mostly, with little system time...
>
> Hmm, that's a curious point; leaves one wondering about possible kernel
> bugs.
>
> > In any event, it seems a bug that merely having connections open causes
> > this problem! They aren't even in transactions...
>
> If the problem is that you've launched far more backends than the system
> can really support, I'd have no hesitation in writing it off as user
> error. "Idle" processes are not without cost. But at this point
> I can't tell whether that's the case, or whether you're looking at a
> genuine performance bug in either Postgres or the kernel.
>
> Can you run strace (or truss or kernel-call-tracer-of-your-choice) on
> the postmaster, and also on one of the putatively idle backends, so
> we can see some more data about what's happening?
>
> regards, tom lane

I wonder if it's a problem with a second SIGUSR2 arriving before the
first is finished? It seems much easier to trigger the effect with more
rapid vacuums than with a delay (even accounting for the reduced number
of vacuums occurring).

Stephen