What runs first: the partitioner or the combiner?

Question

I was wondering between partitioner and combiner, which runs first?

I was of the opinion it is the partitiner first and then combiner and then the keys are redirecte

Answer 1

Combiner is a map side reducer. It means what the reducer performing everything done by combiner. The main use of the combiner is a tuneup/ optimize the performance. After combiner optimize the code, the petitioner separate and assists to get multiple outputs. Combiner is optional, but highly recommendable for large files.

The partitioner divides the data according to the number of reducers and depends on the requirements devides the output. For instance: The output male, female, separate 2 outputs by using partitioner.

First Combiner will come then Partitioner will come, both are come in Mapside only, but not in reducer side.