Re: About RA_PAGES

From: "Dpto. Informatica" <navidul@retemail.es> > >mars1972@my-deja.com wrote: > > > > > RA_PAGES 1000 # Number of pages to attempt to read> > > > ahead > > > > RA_THRESHOLD 500 # Number of pages left before next> > group > > > > > > Or the bigger question (to me): > > > How did you arrive at those values for your RA variables?? > > > -- > > > John Carlson > > > Informix DBA > > > WHSmith USA > > > > > > > Definitely. In the Performance Tuning guide, they state quite clearly > > that the RA_PAGES shouldn't be set higher than 32, for this very reason. > > Try RA_PAGES at 32 and RA_THRESHOLD at 16 or 24 so so. What's > > happening is each of the aoi threads is being forced to read 1000 * > > PAGE_SIZE, or probably either 2 or 4 MB into memory for every 500 read. > > I bet your ra pages used is in the gutter. > > > >--- > > Sorry, I haven't the documentation 'Performance Tuning Guide', I've >only >the 'Performance Guide', where I've used the follow formula, in page 3-60: > >RA_PAGES = (BUFFERS * bp_fact) / ( 2 * large_queries) + 2 >RA_THRESHOLD = (BUFFERS * bp_fact) / ( 2 * large_queries) - 2 > >bp_fact = Portion of data buffers to use large scans that require >read-ahead > i.e.: 75 percent off buffers. > >large_queries = number of concurrent queries that require read-ahead that >you intend to support. > >This information is OLD or is more new than you have ?. > >If my information is not correct, then I will use RA_PAGES = 32 and >RA_THRESHOLD = 24. The thing is, your disk probably can't keep up with such large read-aheads, so you're wasting a lot of effort. ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com