Re: bufwaits and RA_PAGES

Art, I have seen different posts on the BR formula. BR = (bufwaits / (dskreads + bufwrits)) * 100.00 See below first and BR = (bufwaits / (pagereads + bufwrits)) * 100.00 See below second Which one is the correct formula? Thanks Kernoal Please respond to kagel@bloomberg.net To: informix-list@iiug.org Subject: Re: bufwaits and RA_PAGES BUFWAITS can have three causes: 1) Severe buffer starvation (ie need lots more buffers) 2) Excessive readahead, or RA_PAGES & RA_THRESHOLD too large or close together 3) Too few LRUS (most commmon cause!) Your new RA parameters are IMMENSE, unless your storage farm us made up of several older clerks with pencil and keyboard ;-) you cannot need 2K read ahead, chances are that will push the bufwaits higher! To determine if your BUFWAITS is reasonable given your load (some waits are unavoidable as many processes may just need the same buffers at the same time and so will have to wait) calculate the BUFWAIT Ratio (BR): BR = (bufwaits / (dskreads + bufwrits)) * 100.00 A reasonable BR value is under 10% with the ideal at 7% or less. Anything over 10% is usually death. For the onstat -p you posted the formula gives: BR = (3187033 / (40054626 + 29804841)) * 100.00 = 4.56% Which is excellent! No worries mate. At least not on this one. Note that NOAGE is very important on HP as HP/UX is aggressive about aging long running processes meaning that before long your oninits are running at a very low priority! Unless nothing else is running on that machine this can severely affect performance. FWIW. [SNIP] > On this special machine the DB resides on normal disks, but usually we > use RAID5 - would this > make any difference? Singleton disks will have slower overall response time and require more readahead than any striped array. BTW I STRONGLY recommend AGAINST using RAID5 for Informix database disks (my reasons are elsewhere in the CDI archives search for it) and I recommend instead RAID10 first choice followed by RAID 3 or RAID 4. If you are using singleton drives, are you using Informix mirroring for redundancy? Good idea! Art S. Kagel *********************************** second ***************************************** Rob Gale wrote: > > Oh wise gurus...your advice please... [SNIP] > Profile > dskreads pagreads bufreads %cached dskwrits pagwrits bufwrits %cached > 64800092 101527218 3401510871 98.09 6868834 9821955 32234899 78.69 > [SNIP] > bufwaits lokwaits lockreqs deadlks dltouts ckpwaits compress seqscans > 7884672 0 2730403448 0 0 1257 672142 70099 BUFWAITS ratio: (7884672 / (101527218 + 32234899)) * 100 = 5.98454% That's OK. [SNIP] > Profile > dskreads pagreads bufreads %cached dskwrits pagwrits bufwrits %cached > 64800393 101527530 3401750070 98.10 6868844 9822051 32236046 78.69 > [SNIP] > bufwaits lokwaits lockreqs deadlks dltouts ckpwaits compress seqscans > 7884770 0 2730489989 0 0 1257 672174 70103 BUFWAITS ratio: (7884770 / (101527530 + 32236046)) * 100 = 5.89455% So is that and the ratio of the differences is at about 6.72% which is still OK.