Re: Read-ahead parameters

In "Performance Guide for IDS" book( for IDS V7.30), I found this: RA_PAGES = ( BUFFERS*bp_fract ) / ( 2*large_queries ) + 2 RA_THRESHOLD = ( BUFFERS*bp_fract ) / ( 2*large_queries ) - 2 bp_fract is the portion of data buffers to use for large scans that require read-ahead. If you want to allow large scans to table up to 75 percent of buffers, bp_fract would be 0.75 large_queries is the number of concurrent queries that require read-ahead that you intend to support. I setup our testing enviornment according this, a huge number. I am loading data to setup 20G database. Till now the loading is ok, but checkpoint time is over 20. So I don't know what exactly these parameters should be. Vivian vyao@dehavilland.ca Doug McAllister <doug.mcallister@fmr.com> on 05/18/99 04:32:41 PM Please respond to Doug McAllister <doug.mcallister@fmr.com> To: informix-list@iiug.org cc: (bcc: Vivian Yao/deHavilland/Bombardier) Subject: Re: Read-ahead parameters I have read somewhere that the max value for read ahead is 32. I do not remember where and I cannot find a reference to a max value in any doc. Any references? Doug McAllister Fidelity Investments "Carlson@WHSmith" wrote: > IDS 7.30.uc7 > HPUX 10.20 > > The bugs are supposed to be gone; after eight months I'm ready to > reenable read-aheads. > > Our original values of RA_PAGES / RA_THRESHOLD were 150 / 75. These > seemed a bit high based on the postings that I've seen since that time. > We're an OLTP shop, with batch (report) processing thrown in for good > measure. All of our queries run on some index; we have no large > sequential table scans. Our disks are 4GB FW SCSI. > > I'm planning to start at values of 64 / 32. Any thoughts, comments, or > experiences? > > John Carlson > Informix DBA > WHSmith USA