IN- The data type processed by the combine function.
OUT- The data type emitted by the combine function.
@Public @FunctionalInterface public interface GroupCombineFunction<IN,OUT> extends Function, Serializable
GroupReduceFunctionand "pre-reduce" the data. The combine functions typically do not see the entire group of elements, but only a sub-group.
Combine functions are frequently helpful in increasing the program efficiency, because they allow the system to reduce the data volume earlier, before the entire groups have been collected.
This special variant of the combine function supports to return more than one element per group.
It is frequently less efficient to use than the
values- The elements to be combined.
out- The collector to use to return values from the function.
Exception- The function may throw Exceptions, which will cause the program to cancel, and may trigger the recovery logic.
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