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DDL). Second, there is a method to do DDL over a database link, in a fashion, using the job queue facility, DBMS_JOB or, in Oracle 10g, the scheduler package, DBMS_SCHEDULER. Instead of trying to do DDL over the link, you use the link to schedule a remote job to be executed as soon as you commit. In that fashion, the job runs on the remote machine, is not a distributed transaction, and can do the DDL. In fact, this is the method by which the Oracle Replication Services perform distributed DDL to do schema replication.

Autonomous transactions allow you to create a transaction within a transaction that will commit or roll back changes independently of its parent transaction. They allow you to suspend the currently executing transaction, start a new one, do some work, and commit or roll back all without affecting the currently executing transaction state. Autonomous transactions provide a new method of controlling transactions in PL/SQL and may be used in Top-level anonymous blocks Local (a procedure in a procedure), stand-alone, or packaged functions and procedures Methods of object types Database triggers

Before we take a look at how autonomous transactions work, I d like to emphasize that this type of transaction is a powerful and therefore dangerous tool when used improperly. The true need for an autonomous transaction is very rare indeed. I would be very suspicious of any code that makes use of them that code would get extra examination. It is far too easy to accidentally introduce logical data integrity issues into a system using them. In the sections that follow, we ll discuss when they may safely be used after seeing how they work.

The best way to demonstrate the actions and consequences of an autonomous transaction is by example. We ll create a simple table to hold a message: ops$tkyte%ORA11GR2> create table t ( msg varchar2(25) ); Table created. Next, we ll create two procedures, each of which simply INSERTs its name into the message table and commits. However, one of these procedures is a normal procedure and the other is coded as an autonomous transaction. We ll use these objects to show what work persists (is committed) in the database under various circumstances. First, here s the AUTONOMOUS_INSERT procedure: ops$tkyte%ORA11GR2> create or replace procedure Autonomous_Insert 2 as 3 pragma autonomous_transaction; 4 begin 5 insert into t values ( 'Autonomous Insert' ); 6 commit; 7 end; 8 / Procedure created.

Note the use of the pragma AUTONOMOUS_TRANSACTION. This directive tells the database that this procedure, when executed, is to be executed as a new autonomous transaction, independent from its parent transaction.

compilation option. Other pragmas are available. Refer to the PL/SQL programming manual; you ll find a list of them in its index.

And here s the normal NONAUTONOMOUS_INSERT procedure: ops$tkyte%ORA11GR2> create or replace procedure NonAutonomous_Insert 2 as 3 begin 4 insert into t values ( 'NonAutonomous Insert' ); 5 commit; 6 end; 7 / Procedure created. Now let s observe the behavior of the nonautonomous transaction in an anonymous block of PL/SQL code: ops$tkyte%ORA11GR2> begin 2 insert into t values ( 'Anonymous Block' ); 3 NonAutonomous_Insert; 4 rollback; 5 end; 6 / PL/SQL procedure successfully completed. ops$tkyte%ORA11GR2> select * from t; MSG ------------------------Anonymous Block NonAutonomous Insert As you can see, the work performed by the anonymous block, its INSERT, was committed by the NONAUTONOMOUS_INSERT procedure. Both rows of data were committed, so the ROLLBACK command had nothing to roll back. Compare this to the behavior of the autonomous transaction procedure: ops$tkyte%ORA11GR2> delete from t; 2 rows deleted. ops$tkyte%ORA11GR2> commit; Commit complete. ops$tkyte%ORA11GR2> begin