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RE: nowait cursors in triggers

Khemmanivanh, Somckit

2005-06-09

Replies:

Hey,

I'm no trigger expert and may be way off, but...

Just trying to work out the event flow here...

Session 1 deletes where x =3D 1 (this sets the lock on this row), then =
the
trigger fires and locks the remaining rows

Session 2 tries to delete where x =3D 2, but Sess 1's trigger would have
acquired a lock on this row, thus session 2 waits.=20

To me the trigger for session 2 would not have fired yet since it's
being blocked on the delete process. The trigger is an AFTER delete
trigger but the delete never gets a chance to complete due to the lock
acquired by the first trigger.

Sess 2's select ... for update nowait statement never gets a chance to
execute...By the way is there a way to check if a trigger has fired?

Feel free to correct me if I'm way off. =20


Thanks!=20
-----Original Message-----
From: oracle-l-bounce@(protected)
[mailto:oracle-l-bounce@(protected)
Sent: Wednesday, June 08, 2005 10:22 PM
To: oracle-l@(protected)
Subject: nowait cursors in triggers

Hi all,

Does anyone know of a restriction (documented or otherwise) that
prohibits triggers from using 'for update nowait' cursors ?

Consider the following example:
--------------------------------
SQL> create table T ( x number, y number );

Table created.

SQL> insert into T values (1,1);

1 row created.

SQL> insert into T values (2,1);

1 row created.

SQL> create or replace
2 trigger TRG after delete on T
3 declare
4   cursor C is select * from t
5   where y =3D3D 1
6   for update NOWAIT;
7 begin
8   open c;
9 end;
10 /

Trigger created.

Session 1 then does the following:

SQL> set sqlprompt 'SES1> '
SES1> delete from t where x =3D3D 1;

1 row deleted.

Session 2 then tries to delete a different row, but the
after-statement trigger will then try to
get a nowait lock on both rows:

SQL> set sqlprompt 'SES2> '
SES2> delete from t where x =3D3D 2;

(waiting....waiting....)

Is this correct behaviour ? Why does ses2 not get a "ORA-00054:
resource busy and acquire with NOWAIT specified"

Cheers
Connor

--=3D20
Connor McDonald
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
=3D3D=3D
=3D3D=3D3D
email: connor_mcdonald@(protected)
web:  http://www.oracledba.co.uk

"Semper in excremento, sole profundum qui variat"
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