RE: Tim Gorman's "...Cost-Based Optimizer.doc"

  • From: "Goulet, Dick" <DGoulet@xxxxxxxx>
  • To: <somckit.khemmanivanh@xxxxxxxxxxxxxxxx>, <cmarquez@xxxxxxxxxxxxxxxx>, <mgogala@xxxxxxxxxxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
  • Date: Thu, 16 Jun 2005 13:43:47 -0400

What really gets to me with the CBO is that often a simple /*+ RULE */
does the trick=20

-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Khemmanivanh,
Somckit
Sent: Thursday, June 16, 2005 1:36 PM
To: cmarquez@xxxxxxxxxxxxxxxx; mgogala@xxxxxxxxxxxxxxxxxxxx;
oracle-l@xxxxxxxxxxxxx
Subject: RE: Tim Gorman's "...Cost-Based Optimizer.doc"

Could it be that scattered reads take less time "if" the next block of
data to be read is "actually" adjacent to the last block read, therefore
you wouldn't be incurring seek time as you might with sequential
reads?=3D20


Thanks!=3D20
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Marquez, Chris
Sent: Thursday, June 16, 2005 7:53 AM
To: mgogala@xxxxxxxxxxxxxxxxxxxx; oracle-l@xxxxxxxxxxxxx
Subject: Tim Gorman's "...Cost-Based Optimizer.doc"



One comment / question on OPTIMIZER_INDEX_COST_ADJ;
It seems that on "NON-cached" filesystems (e.g. RAW, OCFS) that there
would/do NOT be a great difference in "db file scattered reads" vs. "db
file sequential reads" AVERAGE_WAITS...as every read from disk (on
non-cached filesystem) is a *real* read from dusk...no OS buffer to
help, no?

Thanks,

Chris Marquez
Oracle DBA



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