On Wed, Dec 12, 2012 at 8:29 AM, David Gould <daveg@sonic.net> wrote:
> We lose noticable performance when we raise fill-factor above 10. Even 20 is
> slower.
Whoa.
> During busy times these hosts sometimes fall into a stable state
> with very high cpu use mostly in s_lock() and LWLockAcquire() and I think
> PinBuffer plus very high system cpu in the scheduler (I don't have the perf
> trace in front of me so take this with a grain of salt). In this mode they
> fall from the normal 7000 queries per second to below 3000.
I have seen signs of something similar to this when running pgbench -S
tests at high concurrency. I've never been able to track down where
the problem is happening. My belief is that once a spinlock starts to
be contended, there's some kind of death spiral that can't be arrested
until the workload eases up. But I haven't had much luck identifying
exactly which spinlock is the problem or if it even is just one...
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company