Re: db file sequential/scattered read

Thank you Jonathan and Kevin for clarifying and my apologies Steve for quoting you out of context.

Regards,
Ivan Bajon, ocp

"Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message news:979151756.2709.0.nnrp-09.9e984b29_at_news.demon.co.uk...
>
> There are two different contexts here -
> Steve is talking about the disk being read
> sequentially - which usually occur because
> Oracle is doing a table scan or index fast full scan
>
> Anjo is talking about a wait event called
> 'db file scattered read' - which usually means
> that Oracle is doing a tablescan or index fast
> full scan (or as Kevin Brand mentioned, 8.1.6
> read-ahead). It is unfortunate that a disk sequential
> read happens to be displayed as an Oracle scattered
> read. The reason is that the read is into scattered
> memory locations, rather than a single sequential
> memory block.
>
>
> --
> Jonathan Lewis
> Yet another Oracle-related web site: http://www.jlcomp.demon.co.uk
>
> Practical Oracle 8i: Building Efficient Databases
>
> Publishers: Addison-Wesley
> See a first review at:
> http://www.ixora.com.au/resources/index.htm#practical_8i
> More reviews at: http://www.jlcomp.demon.co.uk/book_rev.html
>
>
>
> Ivan Bajon wrote in message <93h9gi$eof$1_at_news.inet.tele.dk>...
> >Could someone please clarify whether full table scans cause waits for db
> >file sequential read or scattered reads. I've seen claims on both.
> >
> >Steve Adams says:
> >"Sequential reads occur mainly in connection with full table scans and
 fast
> >full index scans." (Taken from Tips->Disk Configuration for Sequential
 Scans
> >on Ixora)
> >
> >In "Description of Oracle7 Wait Events and Enqueues" (2.36 db file
 scattered
> >read) Anjo Kolk says:
> >"This event is normally an indicator that a Full Table Scan is happening
 on
> >the object identified before."
> >
> >This leaves me confused. Which is it? Both?
> >
> >Regards,
> >Ivan Bajon, ocp
> >
> >
>
>
Received on Wed Jan 10 2001 - 15:41:51 CST