[infinispan-dev] conflicts resolution in DeltaAware

Hi Mircea, I remember you recently mentioned that you have been looking into ways to give the ability to the application to resolve updating conflicts. I don't think you where referring to AtomicMap or any other DeltaAware specifically, but it seems now that we urgently need something like this in OGM. I'm looking into the Delta interface, which defines this single method: DeltaAware merge(DeltaAware d); This looks great to merge an update onto an existing value; But of course the world is made of parallel executing updates, especially so when transactions are involved, so we would like to be able to deal with multiple concurrent updates being applied on the same read value. I'm wondering if we could get something like DeltaAware merge(DeltaAware originalValue, DeltaAware updateA, DeltaAware updateB) throws UnsolvableConflict; As Emmanuel pointed out while implementing OGM, if two different updates are being applied to an AtomicMap, it's possible that the updates relate to different keys in the AtomicMap, and for the OGM usecase we would be totally fine with that and would *not* like the transaction to be rolled back. From my understanding of AtomicMap, if two different keys are changed one transaction will fail (correct?). Of course it's totally possible that both updates where going to affect the same keys, and in this case we want to have the operation rolled back. I don't mean the API I wrote literally, I wrote it like that just to give a general picture of what we need; I'm not really liking the idea of throwing an exception on a potentially frequently occurring event, and also while you could chain such invocations in case of multiple updates arriving on the same key, I think it would be far better to be able to try different combinations - or let the application try to be clever - to try resolving as much non conflicting DeltaAware updates as possible. Considering that each transaction might change multiple keys, it would be awesome to describe the API in such a way that either Infinispan or the application can be "smart" and be able to estimate which transaction could be removed (rolled back) to provide the minimum amount of rolled back transactions. I'm not even sure the policy should favour the maximum amount of transactions, maybe the application wants to favour the highest possible changeset, or a specific important one. Even if we start just implementing the method signature I proposed, that could bring a hell of scalability improvements; possibly not only to HibernateOGM but as far as I understood the TreeCache as well. Ideas? Emmanuel, do you agree this would fit the HibernateOGM needs? Cheers, Sanne