Re: db_file_mutliblock_read_count and physical IO

From: Wolfgang Breitling <breitliw_at_centrexcc.com>
Date: Wed, 18 Aug 2004 10:39:51 -0600
Message-Id: <6.1.0.6.2.20040818103427.02eb3d88@pop.centrexcc.com>

tkprof summarizes and for "disk IO" it counts the number of blocks read, not the number of physical I/O. So if you have 1 scattered read that read 128 blocks, or 16 scattered read that each read 8 blocks, tkprof will report 128 "disk IO"
That is one of the (many) reasons Cary advocates to look at the raw extended sql trace.

At 08:25 AM 8/18/2004, you wrote:
>I did a 10046 trace and verified that I can get up to 128 blocks/IO with
>db_file_multiblock_read_count.
>How do I metric this? I look at my total physical IOs when I did a tkprof
>report and my total number of physical IOs remained the same when I had
>the value set to 8 as when I had it set to 128?
>Before I did this test, my assumption was:
>'Oracle would do less total Physical IOs since I am retrieving more
>blocks per IO.'
>That assumption proved false. Can someone explain why?

Regards

Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com

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Received on Wed Aug 18 2004 - 12:46:08 CDT