Re: Linux/PostgreSQL scalability issue - problem with 8 cores

Jakub Ouhrabka <kuba@comgate.cz> writes:
> we have a PostgreSQL dedicated Linux server with 8 cores (2xX5355). We
> came accross a strange issue: when running with all 8 cores enabled
> approximatly once a minute (period differs) the system is very busy for
> a few seconds (~5-10s) and we don't know why - this issue don't show up
> when we tell Linux to use only 2 cores, with 4 cores the problem is here
> but it is still better than with 8 cores - all on the same machine, same
> config, same workload. We don't see any apparent reason for these peaks.

Interesting.  Maybe you could use oprofile to try to see what's
happening?  It sounds a bit like momentary contention for a spinlock,
but exactly what isn't clear.

> Can this be connected with our heavy use of listen/notify and hundreds
> backends in listen mode?

Perhaps.  Have you tried logging executions of NOTIFY to see if they are
correlated with the spikes?

            regards, tom lane