Table of Contents
See HBase and MapReduce up in javadocs. Start there. Below is some additional help.
When TableInputFormat, is used to source an HBase table in a MapReduce job, its splitter will make a map task for each region of the table. Thus, if there are 100 regions in the table, there will be 100 map-tasks for the job - regardless of how many column families are selected in the Scan.