Read Ahead Parameters

Posted in 1999

Steve Romankiw — Wed, 02 Jun 1999 10:07:54 -0400 — source: Informix-list mailing list archive (1991-1998)

<< I am reposting this message. I don't think it made it through! >> I was recently looking at the same recommended parameters and thought it was rather strange with the numbers I came up with. My environment: BUFFERS=50,000 bp_fact=0.50 # random % large_queries=2 # random queries RA_PAGES = ( BUFFERS*bp_fract ) / ( 2*large_queries ) + 2 = 25,000 / 4 + 2 = 6,250 + 2 = 6,252 RA_THRESHOLD = ( BUFFERS*bp_fract ) / ( 2*large_queries ) - 2 = 25,000 / 4 - 2 = 6,500 - 2 = 6248 The RA_PAGES and RA_THRESHOLD values in the above calculation vary slightly <g> from the previously mentioned 64 / 32 or 16 / 4. Any thoughts? I did a several tests with the above values. My original query took 20 minutes to run. With the above changes, the queries takes 15 mintues. My original settings were the defaults. Steve Romankiw