Take for example problems you can solve with map-reduce. Very easy to parallelize. From the application developers point of view there is no concurrency or sync

Take for example problems you can solve with map-reduce. Very easy to parallelize. From the application developers point of view there is no concurrency or synchronization necessary, because it was already solved in general by the framework. Unfortunately, there are lots of problems, where this is not possible. For example, for a distributed concensus problem the conflict resolution is application-specific.