RE: Script to overcome ORA-54 during DDL
- From: "Powell, Mark D" <mark.powell@xxxxxxx>
- To: "'oracle-l@xxxxxxxxxxxxx'" <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 25 Jun 2004 16:00:09 -0400
Mark, you are correct there is a request parameter to release the lock on
commit (at least from 8.1.7 up, maybe before). I forgot about this because
we do not use it. The default is to not release the lock. We pretty much
limit the use of dbms_lock to preventing duplicate processes from running so
we do not want to release the lock until our programs terminate.
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Bobak, Mark
Sent: Friday, June 25, 2004 3:40 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: Script to overcome ORA-54 during DDL
Hmm....well, as I said, I hadn't tried it...was just thinking out loud, =
a bit.
As to them being held till explicitly released, it looks like there is a
boolean parameter "RELEASE_ON_COMMIT", that controls the behavior? =
(9.2.0.5)
Anyhow, it was just a thought.....
-Mark
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Powell, Mark D
Sent: Friday, June 25, 2004 3:34 PM
To: 'oracle-l@xxxxxxxxxxxxx'
Subject: RE: Script to overcome ORA-54 during DDL
Mark, UL locks once granted are held until released via =
dbms_lock.release or
the session terminates and therefore would cover multiple commits =
actions if
that is what the holding process does.
UL locks are also a relatively expensive resource according to the =
Oracle
documentation and requiring every session to take a share level UL lock =
on a
table and then release it for OLTP type work would be a lot of overhead
relative to the work being done.
IMHO -- Mark D Powell --
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Bobak, Mark
Sent: Friday, June 25, 2004 3:21 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: Script to overcome ORA-54 during DDL
<Caveat: untested concept>
Seems to me, if you have control over the code base, and you know these =
=3D
types of
things will be necessary, you could implement something via DBMS_LOCK.
Any time a DML executes, it could first take a user defined (UL) enqueue
in shared mode. It does it's DML, commit/rollback, and the UL is =3D
released
atomically w/ the DML. Now, you come along and need to do mainenance.
So, you exec dbms_lock on the same UL enqueue, but in exclusive mode,
and if any DML is executing, you'll queue up and wait on that enqueue.
When all pending DML commits/rolls back, you'll get your exclusive
UL lock, and you can do the DDL. While this is going on, all DML will
queue up, till the exclusive lock clears. When you're done w/ the
DDL, release the exclusive lock, all DML continues where it left off.
Hmm...just thought of something. DDL implies commit before and after
the change that it's making. Would that first commit release the
lock on the UL enqueue? Hmmm, maybe that's not such a good idea.
I'll have to test it out.....
-Mark
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Jeremiah Wilton
Sent: Friday, June 25, 2004 2:56 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Script to overcome ORA-54 during DDL
Sometimes when trying to perform DDL on really hot objects (heavy
read/DML), I get:
ORA-00054: resource busy and acquire with NOWAIT specified.
I guess this is because you need to obtain a library cache lock in
order to change the object definition. Since there is no enqueue
mechanism for this resource, you can't just 'lock table ... in
exclusive mode;' All that gives you is a DML lock.
One way to avoid this is to write a PL/SQL routine that uses DBMS_SQL
and spins trying to run the DDL, stopping only when it succeeds. This
seems to work most of the time.
Does anyone have a script for doing the above that they would like to
share?
Please don't tell me to just use dbms_redefinition. That is
unnecessarily complex when the above technique can be used instead.
Thanks
--
Jeremiah Wilton
http://www.speakeasy.net/~jwilton
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