I don't think we are in a position to decide what is a reasonable compromise; we can do better. For example - as Radim suggested - it might seem reasonable to have the older value around for a little while. We'll need a little bit of history of values and tombstones anyway for many other reasons.
Sanne On 12 May 2014 09:37, Dan Berindei <[email protected]> wrote: > Radim, I would contend that the first and foremost guarantee that put() > makes is to leave the cache in a consistent state. So we can't just throw an > exception and give up, leaving k=v on one owner and k=null on another. > > Secondly, put(k, v) being atomic means that it either succeeds, it writes > k=v in the cache, and it returns the previous value, or it doesn't succeed, > and it doesn't write k=v in the cache. Returning the wrong previous value is > bad, but leaving k=v in the cache is just as bad, even if the all the owners > have the same value. > > And last, we can't have one node seeing k=null, then k=v, then k=null again, > when the only write we did on the cache was a put(k, v). So trying to undo > the write would not help. > > In the end, we have to make a compromise, and I think returning the wrong > value in some of the cases is a reasonable compromise. Of course, we should > document that :) > > I also believe ISPN-2956 could be fixed so that HotRod behaves just like > embedded mode after the ISPN-3422 fix, by adding a RETRY flag to the HotRod > protocol and to the cache itself. > > Incidentally, transactional caches have a similar problem when the > originator leaves the cluster: ISPN-3421 [1] > And we can't handle transactional caches any better than non-transactional > caches until we expose transactions to the HotRod client. > > [1] https://issues.jboss.org/browse/ISPN-2956 > > Cheers > Dan > > > > > On Mon, May 12, 2014 at 10:21 AM, Radim Vansa <[email protected]> wrote: >> >> Hi, >> >> recently I've stumbled upon one already expected behaviour (one instance >> is [1]), but which did not got much attention. >> >> In non-tx cache, when the primary owner fails after the request has been >> replicated to backup owner, the request is retried in the new topology. >> Then, the operation is executed on the new primary (the previous >> backup). The outcome has been already fixed in [2], but the return value >> may be wrong. For example, when we do a put, the return value for the >> second attempt will be the currently inserted value (although the entry >> was just created). Same situation may happen for other operations. >> >> Currently, it's not possible to return the correct value (because it has >> already been overwritten and we don't keep a history of values), but >> shouldn't we rather throw an exception if we were not able to fulfil the >> API contract? >> >> Radim >> >> [1] https://issues.jboss.org/browse/ISPN-2956 >> [2] https://issues.jboss.org/browse/ISPN-3422 >> >> -- >> Radim Vansa <[email protected]> >> JBoss DataGrid QA >> >> _______________________________________________ >> infinispan-dev mailing list >> [email protected] >> https://lists.jboss.org/mailman/listinfo/infinispan-dev > > > > _______________________________________________ > infinispan-dev mailing list > [email protected] > https://lists.jboss.org/mailman/listinfo/infinispan-dev _______________________________________________ infinispan-dev mailing list [email protected] https://lists.jboss.org/mailman/listinfo/infinispan-dev
