On Fri, Mar 20, 2009 at 2:26 PM, Joe Uhl <joeuhl@xxxxxxxxx> wrote: > On Mar 17, 2009, at 12:19 AM, Greg Smith wrote: > >> On Tue, 17 Mar 2009, Gregory Stark wrote: >> >>> Hm, well the tests I ran for posix_fadvise were actually on a Perc5 -- >>> though >>> who knows if it was the same under the hood -- and I saw better >>> performance >>> than this. I saw about 4MB/s for a single drive and up to about 35MB/s >>> for 15 >>> drives. However this was using linux md raid-0, not hardware raid. >> >> Right, it's the hardware RAID on the Perc5 I think people mainly complain >> about. If you use it in JBOD mode and let the higher performance CPU in >> your main system drive the RAID functions it's not so bad. >> >> -- >> * Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD > > I have not yet had a chance to try software raid on the standby server > (still planning to) but wanted to follow up to see if there was any good way > to figure out what the postgresql processes are spending their CPU time on. > > We are under peak load right now, and I have Zabbix plotting CPU utilization > and CPU wait (from vmstat output) along with all sorts of other vitals on > charts. CPU utilization is a sustained 90% - 95% and CPU Wait is hanging > below 10%. Since being pointed at vmstat by this list I have been watching > CPU Wait and it does get high at times (hence still wanting to try Perc5 in > JBOD) but then there are sustained periods, right now included, where our > CPUs are just getting crushed while wait and IO (only doing about 1.5 MB/sec > right now) are very low. > > This high CPU utilization only occurs when under peak load and when our JDBC > pools are fully loaded. We are moving more things into our cache and > constantly tuning indexes/tables but just want to see if there is some > underlying cause that is killing us. > > Any recommendations for figuring out what our database is spending its CPU > time on? What does the cs entry on vmstat say at this time? If you're cs is skyrocketing then you're getting a context switch storm, which is usually a sign that there are just too many things going on at once / you've got an old kernel things like that. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
