RE: Tuning methodology (was T3's) and use of NetApp's

Mladen,

Read http://www.hotsos.com/dnloads/1.Holt2000.02.01-Backwards.pdf (by Jeff Holt) for complete details about the difference between Oracle's "scattered" and "sequential" reads.

Read http://www.ixora.com.au/tips/tuning/redo_latches.htm (by Steve Adams) for details on the redo latch question.

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com

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-----Original Message-----
Gogala
Sent: Sunday, August 18, 2002 11:33 PM
To: Multiple recipients of list ORACLE-L

On 2002.08.18 23:48 Cary Millsap wrote:
> >
> > 4. 'db file sequential read' does *not* typically indicate a
> > full-table scan, because 'db file sequential read' events, since
> > Oracle8.0 are almost always single-block read calls (before that,
the
> > event could indicate multi-blocks reads of sort segment blocks into
a
> > PGA).
>
> [DM] Does this parameter measure anything then?
>
> It shows the number of blocks read from the OS via calls to read().

I was told, in a private communication, by a person who used to work for Oracle Support
that oracle is reading indexes via "read" and tables via "readv" call, indicating that
a "sequential" read really refers to to reading indexes and "scattered" refers to reading
tables. Is that a correct interpretation? One more thing, oracle documentation claims that
oracle, as of 8i, first reserves redo copy latch and then, after that, it reserves the
allocation latch. After many hours of trying, I finally gave up trying to understand the
algorithm. Can you, please, shed some light on that? Thanks!

-- 
Mladen Gogala
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Author: Mladen Gogala
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-- 
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Author: Cary Millsap
  INET: cary.millsap_at_hotsos.com

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