RE: DDLs -- was Re: simple question on DDL

Tom - I think you've nailed it. Think of the design decisions that some of Oracle's competitors made in the early days and how silly they seem in retrospect. Anyone remember the row-locking vs. block-locking wars?

   The other aspect that many people don't think of if they have never worked in a vendor's development staff is inertia. You as a developer are assigned a list of tasks which is usually larger than you can accomplish. Marketing bases those tasks on 1) which features will get more customers or 2) what customers are howling about -- where is the ROI? Changing how the kernel works is a high-risk business, so I think you are probably stuck with the way it works, even if you feel it is inconsistent.

   If Oracle did go back and "fix" stuff in this area, there may be customer scripts that rely on this behavior, even if we feel it is inconsistent.

-----Original Message-----
Sent: Friday, January 24, 2003 11:35 AM
To: Multiple recipients of list ORACLE-L

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:
>Cost Based Optimisation
>(see http://www.jlcomp.demon.co.uk/tutorial.html )
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>
>-----Original Message-----
>To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
>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
>
>
>--
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>Author: Jonathan Lewis
> INET: jonathan_at_jlcomp.demon.co.uk
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Hemant K Chitale
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