Chris McDonough wrote at 2004-3-3 04:55 -0500: >(boldly crossposting this to zodb-dev, please respond on one list or the >other but not both) > >That error *appears* to be caused by reaching a state that is impossible >to reach. The code in question is: > > for key in list(self._data.keys(None, max_ts)): > assert(key <= max_ts) > STRICT and _assert(self._data.has_key(key)) > for v in self._data[key].values(): > to_notify.append(v) > del self._data[key] > >The line that says "for v in self._data[key].values()" is the line that >throws the KeyError. But it should be impossible for the code to throw >a KeyError for the expression "self._data[key]" because the "keys" >method of the _data IOBTree just told us that the key named by "key" was >one of its keys via the range search; it should be an invariant.
If we had a low conflict connection, I would understand how this could happen: All BTree leaves are chained together. The "keys" method uses this chain to enumerate the keys. "[]" on the other hand, uses the tree structure to locate its key. Assume that a parallel thread removes a key and commits the transaction while we are in the for loop above. We may read the old state (with the later deleted key) for "keys". During the "for", we receive invalidations for the nodes affected by the deletion. When we access "[key]" we may try to load a tree node which is not yet in the ZODB cache and meanwhile invalidated. When we suppress the resulting "ReadConflictError", we may not find "key" (as it is by now deleted). In my "Transience" implementation, I ignore this exceptional case. I do use a low conflict connection and have to be prepared for this situation. Furthermore, the situation is not problematic: I want to determine sessions that should be deleted. Someone else already did it -- this is fine. No need to do it twice... -- Dieter _______________________________________________ Zope-Dev maillist - [EMAIL PROTECTED] http://mail.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope )
