Re: Currval and buffer gets

I am writing a paper on application efficiency and I have a number of simple tests in that paper that illustrates that in a very efficient application the switch to x$dual can make around a 70-80 percent improvent. But beaware: the test suite only accesses x$dual and not other tables so the impact is large and the application is written in the most efficient way. Running the same test but in a worse efficiency case. shows only a 2-3 percent gain ......

Anjo.

"Khedr, Waleed" wrote:

> Can you guys tell me about all the overhead to resolve the view definition
> to reach the magical X$dual table?
>
> Waleed
>
> -----Original Message-----
> Sent: Tuesday, April 23, 2002 12:58 PM
> To: Multiple recipients of list ORACLE-L
>
> Redefine the view to work on dual and pay the price !!!
> Checked it on oracle 8.1.6 and 9.0.1.
> I will take the risk that maybe in some future date this will not work
> if it can save a lot of resources now.
>
> Yechiel Adar
> Mehish
>
> ----- Original Message -----
> To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> Sent: Tuesday, April 23, 2002 3:13 PM
>
> > what would you do if Oracle removed this x$dual or made it multiple row
> > table in future upgrades?
> >
> > -----Original Message-----
> > To: Multiple recipients of list ORACLE-L
> > Sent: 4/23/02 4:08 AM
> >
> > Hello Gaja
> >
> > Thanks for the detailed info.
> > I created a view and did grant to public.
> > I did 10 selects and they did only 2 buffers get.
> > BTW - describe on x$dual does not work but select * works.
> >
> > Yechiel Adar
> > Mehish
> >
> > ----- Original Message -----
> > To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> > Sent: Monday, April 22, 2002 8:15 PM
> >
> >
> > > Hello Yechiel,
> > >
> > > X$DUAL is an Oracle-internal table "in the SGA" and
> > > will not be shown in an ALL_OBJECTS listing.
> > > Obviously, you need to be SYS to see this. You can do
> > > a describe as SYS and you will see it. Which is the
> > > reason why I recommended creating a view and a public
> > > synonym on the view, so that the application may
> > > reference it without any issues.
> > >
> > > Cheers,
> > >
> > > Gaja
> > >
> > > --- Yechiel Adar <adaryechiel_at_hotmail.com> wrote:
> > > > Hello Gaja
> > > >
> > > > I could not find x$dual. Did select on all_objects
> > > > got zip.
> > > > Oracle 8.1.6.3.4 on NT.
> > > >
> > > > Yechiel Adar
> > > > Mehish
> > > >
> > > > ----- Original Message -----
> > > > To: Multiple recipients of list ORACLE-L
> > > > <ORACLE-L_at_fatcity.com>
> > > > Sent: Sunday, April 21, 2002 8:28 PM
> > > >
> > > >
> > > > > Hi Yechiel,
> > > > >
> > > > > Any full-table-scan in Oracle 8i (or below)
> > > > consumes 4
> > > > > LIOs to the segment header. This number has
> > > > reduced to
> > > > > 2 in 9i. Given that the 1 row that you are going
> > > > after
> > > > > is in 1 data block, there is 1 LIO for the data
> > > > block
> > > > > itself, given you a total of 5 LIOs. You can
> > > > verify
> > > > > this by setting 10046 for the session and looking
> > > > at
> > > > > the trace output.
> > > > >
> > > > > The workaround is to reference x$dual in your
> > > > > application. Alternatively, you can create a view
> > > > on
> > > > > x$dual, create a synonym for it and then go from
> > > > > there. You will incur some I/O for the first
> > > > access of
> > > > > the query (with the synonym), but subsequent
> > > > accesses
> > > > > will incur 0 LIOs against x$dual.
> > > > >
> > > > > Cheers,
> > > > >
> > > > > Gaja
> > > > > --- Yechiel Adar <adaryechiel_at_hotmail.com> wrote:
> > > > > > I did two statspack snapshots, one hour and
> > > > forty
> > > > > > minutes apart.
> > > > > > Then I generated a report and loaded it into
> > > > > > oraperf.com.
> > > > > > In the report I saw that the two SQL statements
> > > > that
> > > > > > where executed the most
> > > > > > times where:
> > > > > >
> > > > > > Select xxxx.currval from dual;
> > > > > >
> > > > > > Select xxxx.nextval from dual;.
> > > > > >
> > > > > > Each one was executed about 90,000 times with 5
> > > > > > buffer gets per execution.
> > > > > > The net result was about 950,000 buffer get for
> > > > > > nextval and currval.
> > > > > >
> > > > > > My question is:
> > > > > > Why should there be about 5 buffer gets per
> > > > > > execution?
> > > > > >
> > > > > > Yechiel Adar
> > > > > > Mehish
> > > > > > --
> > > > > > Please see the official ORACLE-L FAQ:
> > > > > > http://www.orafaq.com
> > > > > > --
> > > > > > Author: Yechiel Adar
> > > > > > INET: adaryechiel_at_hotmail.com
> > > > > >
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> > > > > =====
> > > > > Gaja Krishna Vaidyanatha
> > > > > Director, Storage Management Products,
> > > > > Quest Software, Inc.
> > > > > Co-author - Oracle Performance Tuning 101
> > > > >
> > > >
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> > > =====
> > > Gaja Krishna Vaidyanatha
> > > Director, Storage Management Products,
> > > Quest Software, Inc.
> > > Co-author - Oracle Performance Tuning 101
> > > http://www.osborne.com/database_erp/0072131454/0072131454.shtml
> > >
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> > Author: Khedr, Waleed
> > INET: Waleed.Khedr_at_FMR.COM
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> Author: Yechiel Adar
> INET: adaryechiel_at_hotmail.com
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> Author: Khedr, Waleed
> INET: Waleed.Khedr_at_FMR.COM
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Anjo Kolk
  INET: anjo_at_oraperf.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
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