Re: Physical Logging performance

R'diger M'hl wrote: > "Mark D. Stock" <mdstock@mydassolutions.com> wrote: > > >>R'diger M'hl wrote: >> >>>Good morning everybody, >>> >>>some time ago, I found the tip, that the pages/io should be >>>less than the bufsize (around 75%). Is that true? >> >>Certainly 75% is a good place to be. A lot less than that and you are >>wasting resources. A lot more than that and you have potential for >>performance improvement. Usually the resources you are wasting (as with >>your logical log buffer) are not significant enough to reallocated else >>where. > > > Memory is not the problem, we still have a lot. I'm sure, and the amount you are talking about is nothing. >>>I had a physical bufsize of 16 and always a pages/io of >>>around 15.7 so I increased the bufsize to now 32, but >>>it still shows a high number. >>>Do I need to increase even more? >> >>Yes, in general keep increasing until it starts to drop towards around >>75%. Remember though that this is a cache, and if the system goes down >>you lose your cache. > > > Thanks a lot, Mark. > > When the system crashes it will lose the physical buffer, that > means the before images that are not written to disk. > Isn't that rebuilt during physical and logical recovery when > informix comes up? Yes, as far as I'm concerned, losing your pre-images before they are written to disk is not a problem, so rather maximise performance for those that make it to disk, which hopefully is most of them. ;-) > Thanks, Keith. > > Yes, I was afraid of big numbers, because the Admin Guide speaks > of 32 for normal and 64 for heavy workload. You have perhaps also > defined a high number of buffers? On your comment about recommended values in the manual, these are simply that. You can't expect a manual to hold useful values for every situation. If you are tuning to the 75% rule then you will maximise usage of the buffer, and as Keith said, don't be afraid of large numbers. Cheers, -- Mark. +----------------------------------------------------------+-----------+ | Mark D. Stock mailto:mdstock@MydasSolutions.com |//////// /| | Mydas Solutions Ltd http://MydasSolutions.com |///// / //| | +-----------------------------------+//// / ///| | |We value your comments, which have |/// / ////| | |been recorded and automatically |// / /////| | |emailed back to us for our records.|/ ////////| +----------------------+-----------------------------------+-----------+ sending to informix-list