Buffer Waits Ratio

Hi Everyone, I've been trying to get this ratio down below 10% I've been using a calculation posted on here by Art. ratio = bufwaits/pagreads+bufwrits * 100 at the moment the best result I've had has been 11% when I opted for 71 LRU's .. Howver, when I was using 95 LRU's it seemed to settle on 14%. What other factors do I need to take into account?

Andrew Bland <blanda@hep.bradford.gov.uk> wrote in message news:383D2C9D.1D7000C4@hep.bradford.gov.uk... > Hi Everyone, > > I've been trying to get this ratio down below 10% I've been using a > calculation posted on here by Art. > > ratio = bufwaits/pagreads+bufwrits * 100 > > at the moment the best result I've had has been 11% when I opted for > 71 LRU's .. Howver, when I was using 95 LRU's it seemed to settle on > 14%. What other factors do I need to take into account? Read aheads. RA_PAGES and RA_THRESHOLD has impact on bufwaits. To decrease bufwaits you must decrease this two params. ------------------------------------------------- With best regards, Yuri Dovgart SAP R/3, Informix technical consultant, Informix Certified Professional, Senior System Consultant System Architecture and High Availability Systems, 'Telecominvest' company Email y_dovgart@tci.ukrtel.net ICQ 39284285 > > >

On Thu, 25 Nov 1999 12:33:33 +0000, Andrew Bland <blanda@hep.bradford.gov.uk> wrote: >Hi Everyone, > > I've been trying to get this ratio down below 10% I've been using a >calculation posted on here by Art. > > ratio = bufwaits/pagreads+bufwrits * 100 > > at the moment the best result I've had has been 11% when I opted for >71 LRU's .. Howver, when I was using 95 LRU's it seemed to settle on >14%. What other factors do I need to take into account? > > > I was having the same problem, and the answer I kept getting was - MORE BUFFERS. Well, it worked. But I had to increase the memory on the machine - .5 Gig to 1.5 Gig. Sometimes you don't have that luxury. On the read ahead. Check your read ahead percent used (# Used / (other three read values)). If it is >= 98%, I would rather live with buff waits at 11% because of the values of reading info from buffers that read ahead give you. If buff waits start climbing, then ease back on the read ahead. Maybe decreasing the threashold parameter by itself first, then the read ahead pages. I get good results working with one parameter at a time. I also did the recommended 127 LRU's. That seems to work pretty well too. Another important factor is to trend this info (buff waits and read aheads) over time. Maybe a week, or more. Don't bounce the engine every day trying to tune these parameters. It usually doesn't work that easily. Chris