I found that the error happens when I run the test using some Oracle tool
but worked fine using sqlplus.
Thanks
-----Original Message-----
Sent: Tuesday, April 23, 2002 10:38 PM
To: Multiple recipients of list ORACLE-L
as simultaneously as I could make it on W2K, 9.0.1.2 (which means the
first one was running as I started the second one)
no problems. Now I ran as sys and changed it to x$dual because I got
errors (table or view not found) when I ran as system and used x_$dual
so I don't know if that changed the test
- "Khedr, Waleed" <Waleed.Khedr_at_FMR.COM> wrote:
> Never mess up with Oracle's memory:
>
> It seems that x$dual is not designed for concurrent access. When I
> try to
> run the code below in two simultaneous windows the first one comes
> back and
> the second crash (8173):
>
> declare
> nn number;
> ss1 date;
> ss2 date;
> begin
> ---
> ss1 := sysdate;
> for i in 1..100000 loop
> select 2 into nn from sys.x_$dual;
> end loop;
> ss2 := sysdate;
> dbms_output.put_line('run time using table dual in
> centiseconds='||(ss2 -
> ss1 ) * 24 * 60 * 60 * 100);
> end;
>
>
> If the x$dual gets replaced by dual it works fine.
>
> Can any one duplicate this?
>
>
> Thanks
>
>
> Waleed
>
>
>
> -----Original Message-----
> Sent: Tuesday, April 23, 2002 6:49 PM
> To: Multiple recipients of list ORACLE-L
>
>
> I am writing a paper on application efficiency and I have a number of
> simple
> tests in that paper that illustrates that in a very efficient
> application
> the
> switch to x$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
> > > > > > >
> > > > > > > Fat City Network Services -- (858) 538-5051
> > > > > FAX:
>
=== message truncated ===
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Received on Tue Apr 23 2002 - 21:53:42 CDT
