Hemant,
My guess is that Oracle, at some point in time long ago, decided that DDL's
and DML's should not be mixed together. Because they could not (or did not
want to) deal with the issue, they decided to perform an implicit commit
before any DDL statement was issued. Case closed. This is the way it was
done.
Things have changed in the (more than??) 10 years that this code was
written. We are all smarter and have much more experience in what we would
like to see happen, rather than how it is currently coded. Could Oracle
change this code? Absolutely. Will they? Only if enough people ask for it
to be changed. Would I like to see it changed? No. I really don't see the
need. I think DDL and DML are two different things and should not be mixed
together. If they are mixed together, then developers need to learn how it
works and deal with it.
just my 2 cents.
Tom Mercadante
Oracle Certified Professional
-----Original Message-----
Sent: Friday, January 24, 2003 10:30 AM
To: Multiple recipients of list ORACLE-L
Take your first example :
insert into t1 values (1);
drop table t1;
-- how to deal with self-deadlock ?
insert into t1 values (2);
commit;
Why does Oracle HAVE to commit when the DROP TABLE is issued ?
What if the INSERT had been issued by another session ? Would
the DROP TABLE go through in this session ?
The "self-deadlock" could be handled as an Error -- a Transaction error,
with a message like "cannot drop table when transaction is active in
current session".
A duhveloper who has written a very long-winded .SQL file or procedure
and tries to drop a Table when he has an active transaction should be
caught and "errored" -- he shouldn't be allowed to drop his own table, he
has made a logical error.
Take the second example :
insert into t1 values (1);
drop table t2;
-- how to deal with lock by other user ?
insert into t1 values (2);
commit;
If the DROP TABLE may have to wait for another user who has a lock on T2,
why should the INSERT INTO T1 be committed ? Our user hasn't completed
his transaction yet.
It all depends on what you mean by a "Transaction". The way Oracle has
written DDLs, a "Transaction" ends and is committed when the next DDL
is issued. But that may not be a logical transaction in the real world.
My point is not that the DROP TABLE should be "roll-backable". The DROP
TABLE itself must always commit it's own statement. --- it's own statement.
That is to ensure that a third user does not see inconsistency when running
a transaction accessing T1. But why should the DROP TABLE explicitly
commit the previous statement ? In your example, you have shown that
an inconsistency may arise when a DROP is issued on a table with an
outstanding transaction.
But take the case where :
INSERT INTO T10 values ('a');
-- now I want to, for the heck of it, or bec'ose I'm a bad programmer ...
DROP TABLE XYZ ;
-- oops, my INSERT INTO T10 should be rolled back
-- but the Drop XYZ is independent
ROLLBACK;
Here, unfortunately, the DROP TABLE XYZ had already committed the INSERT
INTO T10.
I didn't want that !
It would have been better if this DROP TABLE XYZ was an Autonomous
Transaction.
But in the first example, the DROP TABLE T1 should return an error.
So, the Oracle Kernel must have some more complexity to see if there's any
outstanding
transaction in the current session [it already checks for other sessions
because they
hold TM locks on the Table !] are pending against the same table being
dropped.
Hemant
At 09:50 AM 23-01-03 -0800, you wrote:
>One question to ask is whether whether all DDL
>use the same strategy. Similarly, if you have
>multiple code paths for "do a ddl call" how much
>more risk of error do you introduce to the kernel.
>Finally how do you get a consistent error response
>to the end user if the error condition of apparently
>identical events can fail in extremely different ways.
>
>Consider the complexities of finding a consistent
>kernel level approach to:
>
>insert into t1 values (1);
>drop table t1;
> -- how to deal with self-deadlock ?
>insert into t1 values (2);
>commit;
>
>insert into t1 values (1);
>drop table t2;
> -- how to deal with lock by other user ?
>insert into t1 values (2);
>commit;
>
>
>
>Regards
>
>Jonathan Lewis
>http://www.jlcomp.demon.co.uk
>
>Coming soon a new one-day tutorial:
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>(see http://www.jlcomp.demon.co.uk/tutorial.html )
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>(see http://www.jlcomp.demon.co.uk/seminar.html )
>
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>
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>
>
>
>-----Original Message-----
>To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
>Date: 23 January 2003 16:31
>
>
> >Arup,
> > I see your point and agree that the DDL should be an autonomous tx.
> >Perhaps an enhancement request is in order? Since Oracle has the
>autonomous
> >tx code, integrating into the kernel should be considered...perhaps
>for
> >Oracle 38i?
> > In the absence of that change, I must disagree and say that ddl must
> >issue a commit. If you look at a combination of your example and
>mine, the
> >problem of waiting transactions still exists. In order to create a
>table,
> >space must be allocated. Again, if fet$ contains only 1 row for the
> >particular file where the table is to be created, there is a
>potential for a
> >serious locking problem.
> >
> >Dan
>
>
>--
>Please see the official ORACLE-L FAQ: http://www.orafaq.net
>--
>Author: Jonathan Lewis
> INET: [EMAIL PROTECTED]
>
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Hemant K Chitale
My web site page is : http://hkchital.tripod.com
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