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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Currval and buffer gets
On ORACLE 8163/Win2K , I got some interesting results
though...
ONE SESSION ONLY
SYS_at_ZETA@RSAKTHI>
run time using table dual in centiseconds=400
PL/SQL procedure successfully completed.
Elapsed: 00:00:03.75
SYS_at_ZETA@RSAKTHI>
SYS_at_ZETA@RSAKTHI>
TWO CONCURRENT SESSIONS
SYS_at_ZETA@RSAKTHI>/
run time using table dual in centiseconds=500
PL/SQL procedure successfully completed.
Elapsed: 00:00:04.17
THREE CONCURRENT SESSION SYS_at_ZETA@RSAKTHI>/ run time using table dual in centiseconds=700
PL/SQL procedure successfully completed.
Elapsed: 00:00:06.59
Notice 100 centiseconds increase in each concurrent session..:)
HTH
RS
--- Lyubomir Petrov <lpetrov_at_yahoo.com> wrote:
> No, I couldn't duplicate this effect
> (8.1.7.0.0/Linux
> and 9.0.1.1.1/Win2k) - 1) first test 2 simultaneous
> sessions and then 2) second test 3 simultaneous
> sessions running.
>
> Regards
> Lyubomir Petrov
>
> --- "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
>
=== message truncated ===
-- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Sakthi , Raj INET: rajan_sakthi_at_yahoo.com Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Wed Apr 24 2002 - 16:53:27 CDT
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