Thread: Postgres function use makes machine crash.

Hi all,

I've been dealing with a problem for the past two days
where a certain sql statement works 2 out of 5 times, and
the other 3 times, it causes the machine (quad Xeon 2.8GHz
+ 792543232 bytes mem, linux kernel  2.4.26-custom, pg ver 7.3.4)
to slow down, and finally grind to a halt. It looks like postgres
gets itself into an insane loop, because no matter how much
shared memory I give it, it uses it all, and then
the kernel starts swapping.

I'm pretty sure it's not the kernel, because I've tried four different
2.4.2* stable kernels, and the same happens.

I've attached the query, and the functions used inside the query,
as well as the table structure and an explain. (I haven't been
able to get explain analyze)

It seems that when I replace the functions used in the query,
with the actual values returned by them (one date in each case),
the query runs in 10 seconds.

I did vacuum analyze, and reindex seemed to  work at one
stage, but now it doesn't anymore.

Is there some limitation in using functions that I do not know
about, or is it a bug?

(It seems to be hanging on the max_fpp('''')
function call from inside the fpp_max_ms() function.)

Please help.

Kind Regards
Stefan

Stef <svb@ucs.co.za> writes:
> I've been dealing with a problem for the past two days
> where a certain sql statement works 2 out of 5 times, and
> the other 3 times, it causes the machine (quad Xeon 2.8GHz
> + 792543232 bytes mem, linux kernel  2.4.26-custom, pg ver 7.3.4)
> to slow down, and finally grind to a halt.

IIRC, PG prior to 7.4 had some problems with memory leaks in repeated
execution of SQL-language functions ... and your query sure looks like
it's going to be doing a lot of repeated execution of those functions.

Please try it on 7.4.2 and see if you still have a problem.

It seems somewhat interesting that you see the problem only sometimes
and not every time, but there's not much point in investigating further
if it turns out the problem is already fixed.

            regards, tom lane

Tom Lane mentioned :
=> Please try it on 7.4.2 and see if you still have a problem.

Will do, and I'll post the results

Thanks!