Regular keys differ from sort keys in that they can be (somehow) sorted,
but their order is not necessarily "intuitive". So regular keys are
sufficient for sortbased grouping, but not for explicit sorting
(groupSort, partitionSort, outputSort).
Right now, this difference is only relevant for POJOs. Since the order of
POJO fields is not (well) defined and they are ordered based on all their
fields, the resulting order is not well defined either.
We can add support for sorting POJOs if these implement Comparable or
somehow define the order of their fields (as proposed in FLINK1665)
20150406 14:34 GMT+02:00 Stephan Ewen <sewen@apache.org>:
> I as that a recent commit introduced the notion of sort key types, which
> have a well defined order.
>
> What is the difference to a regular key? Regular keys are also sortable, so
> why the distinction?
>
