RE: Currval and buffer gets

 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
> > > >
> > > > Fat City Network Services -- (858) 538-5051
> > FAX:
> > > > (858) 538-5051
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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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> =====
> 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
>
> __________________________________________________
> Do You Yahoo!?
> Yahoo! Games - play chess, backgammon, pool and more
> http://games.yahoo.com/
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> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Gaja Krishna Vaidyanatha
> INET: oraperfman_at_yahoo.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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