[ZODB-Dev] Ordering before commit hooks

[Jeremy Hylton]

On 8/22/05, Tim Peters <tim at zope.com> wrote:
> Jim still wonders, and he got me wondering too, whether the `order=` gimmick
> is really needed.  For example, you could have gotten to the same end here
> with the old method, by registering your actions with an object of your own
> creation, and registering just one commit hook with the transaction, where
> that one hook looked at the actions you registered with your own object and
> ran them in whatever order _it_ determined was best.  The ordering logic
> would have been out of ZODB then, not limited to what an integer `order` can
> express, and might even benefit from "ah, if I have to run A, then there's
> no need to also run B or C" kinds of optimizations.

I think that's the right reasoning.  I agree with Jim.

The transaction manager coordinates the actions of unconnected
resource managers.  If there are several transaction participants that
are all part of the same software package, they can provide their own
internal ordering as you suggest.  If they are not related, then
there's no reason to think they care about their order relative to
other participants they know nothing about.  To the extent that
software cares about order, there is likely a simple partial order
(run before X) rather than the total order that order= suggests to me.

> I'm inclined to agree with Jim that `order=` wasn't needed; that it was too
> general for the specific use case we've seen; and that it's not general
> enough for plausible other use cases.
> 
> Should this really go into ZODB 3.5?  The method name change and robustified
> signature were good improvements, and I'd certainly like to keep them.  I
> think the jury is still out on `order`, though.  Anyone else have strong
> feelings for or against it?

Keep it out.

Jeremy