Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

CHAPTER 8 ■ TRANSACTIONS 275
Autonomous Transactions
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 would like to emphasize
that they are 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 an extra looking at. 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.
How Autonomous Transactions 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$tkyte@ORA10G> create table t ( msg varchar2(25) );
Table created.
Next, we’ll create two procedures, each of which simply INSERTs its name into the message
table and commits. However, one of these procedures is a normal procedure and the
other is coded as an autonomous transaction. We’ll use these objects to show what work persists
(is committed) in the database under various circumstances.
First, here’s the AUTONOMOUS_INSERT procedure:
ops$tkyte@ORA10G> 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. That directive tells the database that
this procedure, when executed, is to be executed as a new autonomous transaction, independent
from its parent transaction.