Re: Autonomous Transaction (WIP)

On 04/09/2014 08:44 AM, Pavan Deolasee wrote:
> On Wed, Apr 9, 2014 at 11:03 AM, Rajeev rastogi
> <rajeev(dot)rastogi(at)huawei(dot)com <mailto:rajeev(dot)rastogi(at)huawei(dot)com>> wrote:
>
>
> Though autonomous transaction uses mixed approach of
> sub-transaction as well as main
> transaction, transaction state of autonomous transaction is
> handled independently.
>
>
> Whenever I was asked to have a look at implementing this feature, I
> always wondered about the great amount of global state that a backend
> maintains which is normally tied to a single top transaction. Since AT
> will have same characteristics as a top level transaction, I wonder
> how do you plan to separate those global state variables ? Sure, we
> can group them in a structure and put them on a stack when an AT
> starts and pop them off when the original top transaction becomes
> active again, finding all such global state variables is going to be
> tricky.
I would hope most of this to be solved by having one (read only) virtual
transaction and
then juggling the ATs in a way similar to current subtransaction machinery.

The main differences would be that:

A) the top level transaction stays virtual

and

B) ATs are committed independantly

This would be greatly simplified if we can accept the restriction that
there is only single
snapshot per backend (not per transaction). To me this seems a
completely sensible restriction.

Re syntax, I think we need a way to name the transactions so we can have
a way
to switch between multiple parallel active autonomous transactions.

-----
BEGIN TRANSACTION myfirsttransaction;

do something in myfirsttransaction;

BEGIN TRANSACTION anothertransaction;

do something in anothertransaction;

SET TRANSACTION myfirsttransaction;

more work in myfirsttransaction;

ROLLBACK anothertransaction;

COMMIT; -- or COMMIT myfirsttransaction;
----

Cheers
Hannu

>
> Thanks,
> Pavan
>
> --
> Pavan Deolasee
> http://www.linkedin.com/in/pavandeolasee