Re: Adding BUFFERS slowed Checkpoints

A similar situation has occurred here recently. i increased the buffers = sixfold and moved the cache rate from 94% to 98%, I also increased LRUs = and cleaners to 127. (Struck a bug in going to 128) Checkpoints had been = 0 to 3 seconds, mostly 0 and 1, now I am getting several a day at 4 and 5 = seconds. LRU_MAX_DIRTY and MIN_DIRTY are set a 7 and 3, I have just = decreased to 3 and 1 in the expectation of cutting back the checkpoint = times. If the poster is already at 3 and 1 then it may be worth going = even lower. rgds Peter Tashkoff <tashkop@iname.com> Zespri International Limited Std Disclaimers Apply All rights reserved. No party may use this document to vilify another. Zespri New Zealand Kiwifruit, The World's Finest >>> Jay Aymond <jay@ulife.com> 12/03/98 04:45:29 >>> David & Adina Samson <samsons@netmedia.net.il> wrote: > We had a system with which had a cache read hit rate of 94%. >Originally, the BUFFERS parameter were set to 26,000 (i.e. 52Mb). Since >the machine has 512Mb, we increased the BUFFERS to 132,000 (i.e. >264Mb). This improved the cache hit rate issue. However, it actually >caused some problems. > > Our LRU_MAX_DIRTY and MIN_DIRTY are 3 & 1, respectively. Our >system doesn't write enough to hit the MAX dirty (3% * 132000 buffers = =3D >3960 dirty pages). Therefore, the cleaner threads aren't being used >and all writing is being done at checkpoint time. (On average, we're >writing about 500 pages per checkpoint.) These checkpoints have taken >about 4-5 seconds. In our environment, that's too long. > > How do we shorten the checkpoints? I need them to be on the >order of 1 second each. > Are there kernel parameters that need to be changed when we >increase the BUFFERS so high? > > > We're running OnLine 7.22.UC1 under HP-UX 10.20. > > Thanks in advance for your help. > > > David > >David Samson, Senior Database Researcher dsamson@ndsisrael.com=20 >NDS Technologies Israel Ltd. +972 2-589-4529 >PO Box 23012 Fax: +972 2-589-4578 > Jerusalem, Israel Cellular: +972 51 287 481 > > How many LRU's do you have? You could increase the number of LRU queues --- this would decrease the number of buffers per LRU queue. *************************************************************** Jay Aymond United Life & Annuity Insurance Company Email: jay@ulife.com=20 ***************************************************************