Re: autonomous transactions

> On Wed, Jan 23, 2008 at 05:50:02PM -0500, Tom Lane wrote:
> > Simon Riggs <simon@2ndquadrant.com> writes:
> > >> From looking at how Oracle does them, autonomous transactions are
> > >> completely independent of the transaction that originates them --
> they
> > >> take a new database snapshot. This means that uncommitted changes
in
> the
> > >> originating transaction are not visible to the autonomous
> transaction.
> >
> > > Oh! Recursion depth would need to be tested for as well. Nasty.
> >
> > Seems like the cloning-a-session idea would be a possible
implementation
> > path for these too.
> 
> Oracle has a feature where you can effectively save a session and
return
> to it. For example, if filling out a multi-page web form, you could
save
> state in the database between those calls. I'm assuming that they use
> that capability for their autonomous transactions; save the current
> session to the stack, clone it, run the autonomous transaction, then
> restore the saved one.
> --

You are describing an uncommitted transaction and not an autonomous
transaction.  Transactions in Oracle are not automatically committed
like they are in PostgreSQL.

Here is a basic example of an autonomous transaction: 

create or replace procedure pr_log_error (p_error_message
errorlog.message%type) is 
  pragma autonomous_transaction;
begin
  insert
    into errorlog
         (log_user,
          log_time,
          error_message)
  values (user,
          sysdate(),
          p_error_message);
  commit;
exception
  when others then
    rollback;
    raise;
end;
  

And then you can call it from a procedure like this:

create or replace procedure pr_example is
begin
  null;--do some work
  commit;  --commit the work
exception
  when others
    pr_log_error(p_error_message => sqlerrm);
    rollback;
    raise;
end;

The autonomous transaction allows me to insert and commit a record in
different transaction than the calling procedure so the calling
procedure can rollback or commit.

You can also remove the commit/rollback from pr_example and instead do
it from the anonymous block that calls it.  I just added it to make it
clear that it is a different transaction than the error logging
transaction.



Jon