Re: How do I check LRU contention - onstat -g spi ????

InfoJones wrote: > > How am I certain that I don't have LRU contention going on? > > I understand that onstat -g spi can help - not sure how to read it > though > Will lru contention cause the bufwaits from an onstat -p to increase? [output SNIPPED] You can sometimes gleen LRU contention by looking at the number of spins per loop in the -g spi output, yes. This value should be low for a well tuned system. The best indicator of LRU and buffer contention is what I have called the Bufwaits Ratio which is: BR = bufwaits / (dskreads + bufwrits) * 100 Ideally this ratio should be around 7%, values over 10% are sure death and a quiet system or one with no natural contention will show ratios below 5%. In between 7 and 10% is a no-man's land where you will get intermittent reports of slow performance for short periods. To determine whether buffer contention or LRU contention is involved try to calculate your buffer turnover rate: Buffer Turnovers = (dskreads + bufwrits) / BUFFERS BTR = (Buffer Turnover) / (time since last stats clearing) expressed as turnovers per unit time. If you are turning over your buffer pool more often than a few times an hour you probably need more buffers. Add buffers and check again. -- Art S. Kagel & Family kagel@erols.com

Art S. Kagel & Family <kagel@erols.com> wrote: : InfoJones wrote: : [output SNIPPED] : To determine whether buffer contention or LRU contention is involved : try to calculate your buffer turnover rate: : Buffer Turnovers = (dskreads + bufwrits) / BUFFERS : BTR = (Buffer Turnover) / (time since last stats clearing) expressed : as turnovers per unit time. Should one multiply BUFFERS by page size in the Buffer Turnovers calculation or go with just the value of BUFFERS from the config file? : If you are turning over your buffer pool more often than a few times : an hour you probably need more buffers. Add buffers and check again. : -- : Art S. Kagel & Family : kagel@erols.com -- bothwellno@spam.duke.edu