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

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

-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Khemmanivanh,
Somckit
Sent: Thursday, June 16, 2005 1:36 PM
To: cmarquez_at_collegeboard.org; mgogala_at_allegientsystems.com; oracle-l_at_freelists.org
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_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Marquez, Chris
Sent: Thursday, June 16, 2005 7:53 AM
To: mgogala_at_allegientsystems.com; oracle-l_at_freelists.org 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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