Just back from vacation...

Jeremy Hylton wrote:
On 8/22/05, Tim Peters <[EMAIL PROTECTED]> 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.

But that only works if you have all the code in a single framework. If Zope had a commit hook, and that CPS wanted to add another one that "ran after Zope's", there would be no way to do it.

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.

Yes I agree but the partial order makes the implementation much more complex than a global agreed-on integer scale (you have to deal with the naming of packages, potential loops, etc). I agree though that there has to be some "rough consensus" on what integer mean what (i.e., well-known values for important frameworks).

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.

I don't agree. To me this is an instance of the very general problem of ordering of subscribers (and indeed if ZODB depended on an event system this kind of thing would be done with an event subscriber). And we know very well that we have unresolved issues with the ordering of event subscribers, where the "order" argument would at least introduces some flexibility that we don't have today.

I vote for keeping it in ZODB 3.5


Florent Guillaume, Nuxeo (Paris, France)   CTO, Director of R&D
+33 1 40 33 71 59   http://nuxeo.com   [EMAIL PROTECTED]
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