Andrey, If I leave behind my knowledge about Ignite internals, my expectation would be that an EntryProcessor is invoked on all affinity - both primary and backup - nodes in the grid. The main reason behind this expectation is that usually a serialized EntryProcessor instance is smaller than resulting object being stored in the cache, so sending a serialized EntryProcessor should be cheaper. Is there a specific reason you expect an EntryProcessor to be called only once across all the nodes?
I would not imply any restrictions on how many times an EntryProcessor is called during a cache update. For example, in a case of explicit optimistic READ_COMMITTED transaction it may be called more than once because Ignite needs to calculate a return value for the first invoke() and then it should be called second time during commit when transactional locks are held. Current requirement is that an EntryProcessor should be a stateless function, and it may be called more than once (but of course it will receive the same cache value every time). I agree that this should be properly articulated in the documentation, I will make sure that it will be reflected in the forthcoming 1.5 release javadocs.
