Re: [ZODB-Dev] Conflict resolution (was Re: Notes on using wrapper storages for record transformation)
Le lundi 24 mai 2010 19:13:51, Jim Fulton a écrit : Thanks. Looks tasty. :) I look forward to reading it. BTW, you will probably also be interested by this: http://www.python.org/~jeremy/weblog/030514.html It's old (pre-MVCC), but otherwise interesting. I would love to see an updated version (esp. with the achieved/targetted isolation level). -- Vincent Pelletier ___ 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
[ZODB-Dev] Conflict resolution (was Re: Notes on using wrapper storages for record transformation)
On Mon, May 24, 2010 at 10:57 AM, Vincent Pelletier vinc...@nexedi.com wrote: Le dimanche 23 mai 2010 16:11:44, Jim Fulton a écrit : Getting a bit more out of initial topic: I am currently searching for papers describing how conflict resolution is supposed to happen, and more exactly if it is safe to chain-resolve for a single transaction. IMO, there's nothing particularly safe about conflict resolution. Conflict resolution weakens transaction isolation in ways that can (but generally don't :) produce incorrect transactions. In the future, in addition to doing conflict resolution on the client, I'd like to make it more configurable so that, among other things, it can be disabled. Example, using a similar representation of action as in Atul Adya thesis: Reference? w1(x1) w2(x2) c2 c1 - conflict for x1, based on x0 and to rebase onto x2, so transaction 1 starts resolving. In the meanwhile: w3(c3) c3 w1(x1') c1 - conflict for transaction 1 again. This step can be repeated as many times as desired, then eventually: w1(x1) c1 - success I don't follow the above. I could not find a doc spelling out this case yet. Let me see if I understand the case: If we do conflict resolution before the commit lock is held, then there if a chance that the object under conflict gets updated again while we're doing conflict resolution, so we may have to to conflict resolution again. Is that the case you're talking about? This case can't occur in the current ZODB implementation, so there's nothing written about it. From what you said on lock not being held during the first phase, I infer that it is already standard for this to happen. That's not what I said. I said it gets the lock at the end of the first phase. The lock is held while conflict resolution is performed. Jim -- Jim Fulton ___ 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
Re: [ZODB-Dev] Conflict resolution (was Re: Notes on using wrapper storages for record transformation)
Le lundi 24 mai 2010 17:23:54, Jim Fulton a écrit : Reference? Weak Consistency: A Generalized Theory and Optimistic Implementations for Distributed Transactions http://pmg.csail.mit.edu/pubs/adya99__weak_consis-abstract.html If we do conflict resolution before the commit lock is held, then there if a chance that the object under conflict gets updated again while we're doing conflict resolution, so we may have to to conflict resolution again. Is that the case you're talking about? Yes. That's not what I said. I said it gets the lock at the end of the first phase. The lock is held while conflict resolution is performed. Oops, I didn't realise that ZEO was postponing Storage.store calls until tpc_vote call. I now realise that this is required to not interleave stores from different transactions in underlying storage. -- Vincent Pelletier ___ 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
Re: [ZODB-Dev] Conflict resolution (was Re: Notes on using wrapper storages for record transformation)
On Mon, May 24, 2010 at 3:03 PM, Vincent Pelletier vinc...@nexedi.com wrote: Le lundi 24 mai 2010 17:23:54, Jim Fulton a écrit : Reference? Weak Consistency: A Generalized Theory and Optimistic Implementations for Distributed Transactions http://pmg.csail.mit.edu/pubs/adya99__weak_consis-abstract.html Thanks. Looks tasty. :) I look forward to reading it. Jim -- Jim Fulton ___ 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
