Scheduler Hook Points

Below are suspected locations of interest regarding the CDH3 (0.20.2) task scheduler:

src/mapred/org/apache/hadoop/mapred/TaskScheduler.java - Topmost interface for all schedulers.

src/mapred/org/apache/hadoop/mapred/JobQueueTaskScheduler.java - Default FIFO Scheduler.

src/contrib/fairscheduler - Fair Scheduler.

src/contrib/capacity-scheduler - Another Scheduler.

Classes dealing with block placements

The BlockPlacementPolicy interface and its default implementation BlockPalcementPolicyDefault, used to choose on which machine to put blocks (for each block).