Re: Read ahead & Buffer wait ratio query.

Tony Woods wrote: > > Hello all, > > Below is the formulla I use for calculating the Read Ahead usage : > ((ixdaRA + idxRA + daRA) / RApgsused) * 100 > Many I times I see the percentage is above 100. Does it mean that the page > which was read ahead was read/used twice or more. I don't have a manual to hand, but this must be wrong. You want to see what you used as a percentage of what you read ahead. So it must be: (RApgsused / (ixdaRA + idxRA + daRA)) * 100 > I have seen this formulla in Informix list mails for calculating Buffer wait > ratio or Buffer turnover ratio : > ((bufwaits/(pagreads + bufwrits)) * 100) > Can anybody please explain me the mean of this in simple english? This is looking at the buffer waits as a percentage of buffer IO (reads & writes). I must confess I am not convinced this is the best formula as I often get figures of up to 4000% on very inactive systems. On such systems pagreads is smaller than bufreads, so using bufreads gives a more useful answer. Cheers, -- Mark. +----------------------------------------------------------+-----------+ | Mark D. Stock mailto:mdstock@mydas.freeserve.co.uk |//////// /| | http://www.informix.com http://www.informixhandbook.com |///// / //| | http://www.iiug.org +-----------------------------------+//// / ///| | |This email will self-destruct in |/// / ////| | |10 sec. If you received this email |// / /////| | |in error, sorry about the mess. |/ ////////| +----------------------+-----------------------------------+-----------+