Comments on: Slow Code

By: Event snapshots « Oracle Scratchpad

Event snapshots « Oracle Scratchpad — Sun, 15 Jun 2008 20:13:38 +0000

[...] — Jonathan Lewis @ 8:13 pm UTC Jun 15,2008 Some time ago I wrote a note about using dbms_lock() to slow down your SQL, and followed up with an example of using this type of code to help with [...]

By: Jonathan Lewis

Jonathan Lewis — Fri, 18 May 2007 09:54:31 +0000

Gabe, Alexander: My error. If you want to use a pl/sql function to build a 'function-based index' it has to be deterministic. This has got me into the habit of declaring any function I call from SQL a deterministic function, even though it's not necessary.

By: matthew

matthew — Fri, 18 May 2007 07:06:38 +0000

gabe

thank you, I just didn’t get it at first

By: Gabe

Gabe — Thu, 17 May 2007 18:03:03 +0000

Alexander,

Quite true.
I just kept “building on” … taking the deterministic clause out is indeed all it takes to avoid the caching.

Thanks.

By: Alexander Fatkulin

Alexander Fatkulin — Wed, 16 May 2007 23:46:06 +0000

Gabe,

for your case – why not just get rid of the deterministic clause?

That way you don’t need to play with a rownum’s and such.

By: Gabe

Gabe — Wed, 16 May 2007 16:24:41 +0000

Matthew,

Well, you’re not switching off anything really. You just make it so there is nothing to cache: the cache is based on the input … add something unique, like rownum, and then you’re sleeping on every row. The function remains deterministic.

create or replace function wait_row(
i_v in varchar2,
i_sec in number default 5,
i_rnm in number default 0
) return varchar2
deterministic
parallel_enable
as
begin
sys.dbms_lock.sleep(i_sec);
return i_v;
end;
/

SQL> select wait_row(n,1) from x;

WAIT_ROW(N,1)
————————————————

0001
0000
0001
0000
0001
0000
0001
0000
0001
0000
0001

11 rows selected.

Elapsed: 00:00:03.01
SQL> select wait_row(n,1,rownum) from x;

WAIT_ROW(N,1,ROWNUM)
————————————————

0001
0000
0001
0000
0001
0000
0001
0000
0001
0000
0001

11 rows selected.

Elapsed: 00:00:11.03

Caveats?

By: v$session_wait_history « Oracle Scratchpad

v$session_wait_history « Oracle Scratchpad — Wed, 16 May 2007 10:14:21 +0000

[...] of the first things I did with the wait_row() function that I described in my last blog, was to set up a simple way to emulate this view in 8i and 9i. The code, which has to be run under [...]

By: matthew

matthew — Wed, 16 May 2007 08:30:33 +0000

gabe,

I can’t follow you
Could you please explain ?

Sounds very interesting, can I really switch the caching mechanism on / off ?

By: neil kodner

neil kodner — Tue, 15 May 2007 17:39:13 +0000

Every time I’ve tried to use dbms_lock.sleep(), I’ve run into weird latching problems. This was in the 9.2.0.4. days. I remember that a lot of other things would slow down when I invoked sleep(). Maybe things are different now-would you be willing to run some tests?

By: Gabe

Gabe — Tue, 15 May 2007 15:36:53 +0000

A third parameter defaulted to 0 would allow to – effectively – bypass or allow the caching mechanism by passing or not passing in the rownum. Would it not?