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See the source code of the Hour partitioner plugin:
The Partitioner class: HourPartitioner.java
The Dialog class: HourPartitionerDialog.java
The hour partitioner takes the name of a file to partition on. The name of the file contains the hour on which the data was captured and we want to use this to partition on. For example: Weblogs-20100329-23.txt This partitioner takes the 23 from the filename, turns it into an integer and calculates the remainder of the division by the number of partitions in the partitioning schema.