[PERFORM] Strange performance response for high load times

2009-06-18 Thread Peter Alban
Hi All, We are having a reasonably powerful machine for supporting about 20 databases but in total they're not more then 4GB in size. The machine is 2 processor 8 core and 8 Gig or ram so I would expect that PG should cache the whole db into memory. Well actually it doesn't. What is more

Re: [PERFORM] Strange performance response for high load times

2009-06-18 Thread Kenneth Marshall
On Thu, Jun 18, 2009 at 08:27:02PM +0200, Peter Alban wrote: Hi All, We are having a reasonably powerful machine for supporting about 20 databases but in total they're not more then 4GB in size. The machine is 2 processor 8 core and 8 Gig or ram so I would expect that PG should cache the

Re: [PERFORM] Strange performance response for high load times

2009-06-18 Thread Peter Alban
So Ken , What do you reckon it should be ? What is the rule of thumb here ? cheers, Peter On Thu, Jun 18, 2009 at 8:30 PM, Kenneth Marshall k...@rice.edu wrote: On Thu, Jun 18, 2009 at 08:27:02PM +0200, Peter Alban wrote: Hi All, We are having a reasonably powerful machine for

Re: [PERFORM] Strange performance response for high load times

2009-06-18 Thread Kenneth Marshall
On Thu, Jun 18, 2009 at 09:42:47PM +0200, Peter Alban wrote: So Ken , What do you reckon it should be ? What is the rule of thumb here ? cheers, Peter It really depends on your query mix. The key to remember is that multiples (possibly many) of the work_mem value can be allocated in an

Re: [PERFORM] Strange performance response for high load times

2009-06-18 Thread Peter Alban
What's still badgering me , is the performance when, there is no load or significantly lower than peek times ? Why is there such a big difference ? i.e. off peek times a simple select with where (on indexed column) and limit taks* 40 ms* during peek times it took *2 seconds* - 50 times slower

Re: [PERFORM] Strange performance response for high load times

2009-06-18 Thread Kevin Grittner
Peter Alban peter.alb...@gmail.com wrote: Why is there such a big difference ? i.e. off peek times a simple select with where (on indexed column) and limit taks* 40 ms* during peek times it took *2 seconds* - 50 times slower ! If your high work_mem setting you may have been causing the