Hive supports indexes, which are used for filters currently.
It would be very useful to add support for index-based joins in Hive.
If 2 tables A and B are being joined, and an index exists on the join key of A,
B can be scanned (by the mappers), and for each row in B, a lookup for the corresponding row in A can be performed.
This can be very useful for some usecases.