[Zope] ZODB.POSException.ConflictError (in custommade product)

[Dieter Maurer]

Gitte Wange wrote at 2003-11-3 10:12 +0100:
 > ....
 > > I said: your counter (any one of them) in the ZODB should become
 > > a "BTrees.Length.Length" instance. I thought, this were pretty clear.
 > 
 > Now it's pretty clear :-)
 > I updated the counts to be a BTrees.Length instance instead of just an 
 > integer.
 > Looks like it helped but we still see the error sometimes (not as often as 
 > before).
 > The code for updating the counts look like this:
 > 
 > def addCount(self, url):
 >         """
 >         Add a new count for an url
 >         """
 >         counts = self._counts
 >         if not url in counts.keys():
 >             counts[url] = Length(0)
 >         counter = counts[url]
 >         counter.change(1)
 >         counts[url] = counter
 >         self._counts = counts
 >         self._p_changed = 1
 > 
 > Guess the error is raised when assigning the counts to self._counts.
 > I have experienced before that dictinaries don't survive a restart of Zope if 
 > not saving them as above but maybe this can work:

Yes, probably.

Make your "_counts" an "BTrees.OOBTree.OOBTree" instance (which is
itself a persistent object).
You can then drop "self._counts= counts" and "self._p_changed = 1".

 > ...
 > def addCount(self, url):
 >         """
 >         Add a new count for an url
 >         """
 >         if not url in self._counts.keys():
 >             counts = self._counts
 >             counts[url] = Length(0)
 >             self._counts = counts
 >             self._p_changed = 1
 >         counter = self._counts[url]
 >         counter.change(1)
 > 
 > Would that work ?

Yes.

 > > That said: you may want to replace the dictionary by a
 > > "BTrees.OOBTree.OOBTree" instance.
 > > This way, the conflict resolution of "OOBTrees" may prevent
 > > (most) concurrent writes to the mapping (when you add
 > > new entries to the mapping) causing exceptions.
 > > It may not be necessary, though, as you probably rarely add
 > > new entries (usually, you will count in already existing counters).
 > 
 > It's very rarely that I will add new entries - all existing pages already 
 > exist in the tool.

Then, you *can* stay with a dictionary.
But an "OOBTree" would still give you easier code (no "_p_changed = 1").

-- 
Dieter