On 08/30/2010 03:36 PM, Jim Fulton wrote: > The tricky thing about this is the last paragraph. If the method > doesn't raise an error, then there can't be updates to the object > until after the transaction commits. For most current > implementations, this implies that the storage lock is help when this > is called. For ZEO, some special care will be necessary because the > storage lock isn't acquired until the very end of the first phase of > 2-phase commit. > > I'm particularly concerned about the impact on RelStorage.
Thanks for calling attention to this. Like ZEO, RelStorage doesn't acquire the commit lock until the end of the first phase of 2-phase commit, for performance reasons. Therefore, if I understand correctly, ZEO and RelStorage will have to maintain a list of OID/serials that the transaction is depending on, then check that list after the commit lock is acquired (but still in the first phase). If anything has changed, we should raise a ReadConflictError. Does that sound right? BTW, perhaps the method name and signature could be as simple as "require(oid, serial)". It simply declares to the storage that the transaction requires a specific version of an object. Shane _______________________________________________ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org https://mail.zope.org/mailman/listinfo/zodb-dev