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Note that while resolvers which implement the GenericUDAFResolver2 interface are provided the extra information regarding the presence of DISTINCT qualifier of invocation with the wildcard syntax, they can choose to ignore it completely if it is of no significance to them. The underlying data filtering to compute DISTINCT values is actually done by Hive's core query processor and not by the evaluator or resolver; the information is provided to the resolver only for validation purposes. The AbstractGenericUDAFResolver base class offers an easy way to transition previously written UDAF implementations to migrate to the new resolver interface without having to re-write the implementation since the change from implementing GenericUDAFResolver interface to extending AbstractGenericUDAFResolver class is fairly minimal. (There may be issues with implementations that are part of an inheritance hierarchy since it may not be easy to change the base class.) a