Oracle-L: RE: Cache on sysdate? --From 9i performance planning manual

From: Jamadagni, Rajendra <Rajendra.Jamadagni_at_espn.com>
Date: Thu, 26 Dec 2002 14:14:14 -0800
Message-ID: <F001.00522A59.20021226141414@fatcity.com>

Richard,

If you look in the tracefile ... there is no select from dual. It used to be like that but things changed (as Anjo mentions maybe be around 8iR3). The sysdate call is now a C function call.
Raj

Rajendra Jamadagni MIS, ESPN Inc.
Rajendra dot Jamadagni at ESPN dot com
Any opinion expressed here is personal and doesn't reflect that of ESPN Inc.

QOTD: Any clod can have facts, but having an opinion is an art!

-----Original Message-----
Sent: Thursday, December 26, 2002 3:59 PM To: Multiple recipients of list ORACLE-L

That's because doing dt := sysdate is more optimized, it's still select sysdate into dt from dual but more optimized. select from dual doing 4 db block gets in 8i and 2 db block gets in 9i, but you can tune it to cut it down.

Richard Ji

-----Original Message-----
Sent: Thursday, December 26, 2002 2:45 PM To: Multiple recipients of list ORACLE-L

That's what I thought too. But the results of testing are somewhat different.
Maybe it's evaluated within the PL/SQL engine and does not require a context

switch to the SQL engine.

Platform : Sun Solaris 2.6
Oracle : 8.1.7.4 (32 bit)

DEV:43#14739-23049>@dual1
DEV:43#14739-23049>declare
  2 dt date;
  3 begin
  4

  5          for i in 1..10000
  6          loop
  7      select sysdate into dt from dual;

8 -- dt := sysdate;
9 end loop;
10 end;
11 /

PL/SQL procedure successfully completed.

Elapsed: 00:00:01.97

DEV:43#14739-23049>@dual1
DEV:43#14739-23049>declare
  2 dt date;
  3 begin
  4

  5          for i in 1..10000
  6          loop
  7  --    select sysdate into dt from dual;
  8      dt := sysdate;

9 end loop;
10 end;
11 /

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.92

Regards,
Denny

Quoting K Gopalakrishnan <kaygopal_at_yahoo.com>:

> Raj:
>
> Both are same. It is internally translated as a select call to dual.
>
> KG
>
> --- "Jamadagni, Rajendra" <Rajendra.Jamadagni_at_espn.com> wrote:
> > Can someone please explain me why you have to use
> >
> > select sysdate
> > from dual
> > /
> >
> > when
> >
> > my_date_Var := sysdate;
> >
> > just works fine? Maybe I am clueless ... but I can take an
> > explanation
> >
> > Raj
>
> =====
> Have a nice day !!
> ------------------------------------------------------------
> Best Regards,
> K Gopalakrishnan,
> Bangalore, INDIA.

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Received on Thu Dec 26 2002 - 16:14:14 CST