Hi Ken, OK - maybe there is a bit of conflicting info here - Let's begin by saying you must try and have the hit ratio above 99% for optimum performance (As stated in the performance and Tuning manual). If you look at selftunebufpoolsize - it will adjust the buffpool when your cache hit ratio is below 98% - indicating the general rule that 98% is the cut-off point for acceptable performance. Above 97%(in my mind anyhow is 98% or higher in any case). I think what it should state is that it should not be lower than 98%.... Anycase - I've got experience on both sides of this figure - 96-97% hit ratio my server was performing like a dog - and you will only see this in expiration processing and big SQL queries - some of my queries that create reports was running for 5 hours - they now run in about half an hour. When you get a techie phoning you and saying he's been waiting for an hour already just to get the list of files to pick from during a restore you will know what I'm talking about.
The cache hit is now sitting at 99.11 and the performance from everything is excellent. When your cache hit ratio goes lower than 98% it indicates that you have a performance problem somewhere - it might be like in our case where our mainframe was running 100% CPU most of the day and night - increasing the buffpoolsize in this case meant nothing. Once we solved the CPU utilisation issues (By moving workload off this mainframe), our cache hit ratio went back up and performance is excellent. So there you have it: 96%-97% - bad performance 97%-98% - OK - but not good (Let's call it acceptable) 98%-99% - Good performance 99%-100% - Excellent performance Hope this helps! Regards Christo ---------------------------------------------------------------------- No experience. I fact I'm learning from your experience. While you say "from my training at IBM that a cache hit rate of 99% and above is recommended" I found the following statement in the web interface. The server database performs best with a cache hit ratio above 97% in the database bufferpool. To tune the bufferpool size, (a) reset the bufferpool statistics, (b) execute server operations that use the database, and (c) view the database details to see if the cache hit ratio is above 97%. If the cache hit ration is NOT above this percentage, increase the size of the BUFPOOLSIZE specification in the server options file. Conflicting advice? Perhaps your 97.7% is good and no problem exists. Let's hear from others. Please...... Ken [EMAIL PROTECTED] >>> [EMAIL PROTECTED] 08/21/2002 12:46:04 AM >>> Hi all, first I've to thank all participants for the amount of answers I got on my latest questions. Now I've got a new one which relates on the bufferpoolsize and the cache hit rate on OS/390 TSM-Servers. we use the following bufpoolsize: 32768 our chache hit rate: 97,7 % I know from my training at IBM that a cache hit rate of 99 % and above is recommended. Is it possible, that a lower cache hit rate can cause performance-problems? What is your experience? MfG Sascha Br�uning Sparkassen Informatik, Fellbach OrgEinheit: 6322 Wilhelm-Pfitzer Str. 1 70736 Fellbach Telefon: (0711) 5722-2144 Telefax: (0711) 5722-1630 Mailadr.: [EMAIL PROTECTED] ______________________________________________ "The information contained in this communication is confidential and may be legally privileged. It is intended solely for the use of the individual or entity to whom it is addressed and others authorised to receive it. If you are not the intended recipient you are hereby notified that any disclosure, copying, distribution or taking action in reliance of the contents of this information is strictly prohibited and may be unlawful. Absa is liable neither for the proper, complete transmission of the information contained in this communication, nor for any delay in itsreceipt, nor for the assurance that it is virus-free."
