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

My take on that is that in a real multi-user system, the chance that "the next block of data to be read is "actually" adjacent to the last block read" is virtually nil. By the time your session issues the next scattered read, someone else will have "kidnapped" the read head and left it somewhere else on the disk.
I believe that if scattered, i.e. multi-block, reads are faster than sequential, i.e. single-block, reads it is because the SAN recognized a read pattern and prefetched the next bunch of block into the cache.

Khemmanivanh, Somckit wrote:

> 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?=20
>
>

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Regards

Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com
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