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From "Matei Zaharia (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-706) Support for FIFO pools in the fair scheduler
Date Sat, 04 Jul 2009 01:36:47 GMT
Support for FIFO pools in the fair scheduler
--------------------------------------------

                 Key: MAPREDUCE-706
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-706
             Project: Hadoop Map/Reduce
          Issue Type: New Feature
          Components: contrib/fair-share
            Reporter: Matei Zaharia


The fair scheduler should support making the internal scheduling algorithm for some pools
be FIFO instead of fair sharing in order to work better for batch workloads. FIFO pools will
behave exactly like the current default scheduler, sorting jobs by priority and then submission
time. Pools will have their scheduling algorithm set through the pools config file, and it
will be changeable at runtime.

To support this feature, I'm also changing the internal logic of the fair scheduler to no
longer use deficits. Instead, for fair sharing, we will assign tasks to the job farthest below
its share as a ratio of its share. This is easier to combine with other scheduling algorithms
and leads to a more stable sharing situation, avoiding unfairness issues brought up in MAPREDUCE-543
and MAPREDUCE-544 that happen when some jobs have long tasks. The new preemption (MAPREDUCE-551)
will ensure that critical jobs can gain their fair share within a bounded amount of time.

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