Re: db_file_mutliblock_read_count and physical IO
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Wed, 18 Aug 2004 10:39:51 -0600
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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