Why are reduce tasks always pending?
The reduce tasks of a MapReduce job will not be dispatched to run if the MapReduce application is not pre-started and the runReduceTaskOnMapSlot setting is disabled.
To avoid this situation, do one of the following:
- Allow a MapReduce application to be pre-started. This is the default configuration.
- Allow reduce tasks to run on a map task's slot. This is a common configuration for optimized MapReduce performance.