Re: Nested xacts: looking for testers and review

On Wed, May 26, 2004 at 04:35:52PM -0700, Stephan Szabo wrote:

> On Wed, 26 May 2004, Alvaro Herrera wrote:
>
> > I'm missing one item: deferred triggers. The problem with this is that
> > the deftrig queue is not implemented using normal Lists, so there's no
> > efficient way to reassign to the parent when the subtransaction commits.
> > Also I'm not sure what should happen to the "immediate" pointer --- a
> > subtransaction should have it's own private copy, or it should inherit
> > the parent's? Please whoever implemented this speak up (Stephan
> > Szabo?), as I'm not sure of the semantics.
>
> The immediate pointer basically points at the end of the queue from the
> last scanning of the trigger queue (since any "immediate" triggers from
> before that would have been run at that time there's no reason to scan
> from the beginning).

Hmm. You assume correctly that a subtransaction has (or will have) a
private queue. But we do not consider a subtransaction to be somewhat a
separate entity -- the principle is that the transaction has to feel
just like the BEGIN wasn't there. So

BEGIN;
UPDATE foo ...
UPDATE bar ...
COMMIT

has to be exactly the same as

BEGIN;
BEGIN;
UPDATE foo ...
COMMIT;
BEGIN;
UPDATE bar ...
COMMIT;
COMMIT;

Now, with that in mind: is it correct that the "immediate" pointer
points to the beginning of the subtransaction's private deferred trigger
queue, at subtransaction's start?

Now, at subtransaction end, lets suppose I concatenate the list the
original transaction had with the subtransaction's private list. What
should the immediate pointer be?

When is the immediate pointer advanced? I know it's "during scanning of
the list", but when is this? At the end of each query?

> If one sets a constraint to immediate in a subtransaction, does/should
> it cause the immediate check of pending events from its parent? And
> does that revert when the transaction ends?

Yes, I think it should fire all events, including the parent's. Good
point; it means there has to be a way of getting the whole list, from
the topmost transaction, in order :-(

I'm not sure what you mean by reverting though.

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
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