RE: Currval and buffer gets

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
> > > > >
> > > > > Fat City Network Services -- (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
> >
> > __________________________________________________
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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: Yechiel Adar
  INET: adaryechiel_at_hotmail.com

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Author: Khedr, Waleed
  INET: Waleed.Khedr_at_FMR.COM

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