Free temporary space should be modelled better
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Key: HADOOP-657
URL: http://issues.apache.org/jira/browse/HADOOP-657
Project: Hadoop
Issue Type: Improvement
Components: mapred
Affects Versions: 0.7.2
Reporter: Owen O'Malley
Assigned To: Owen O'Malley
Currently, there is a configurable size that must be free for a task tracker to
accept a new task. However, that isn't a very good model of what the task is
likely to take. I'd like to propose:
Map tasks: totalInputSize * conf.getFloat("map.output.growth.factor", 1.0) /
numMaps
Reduce tasks: totalInputSize * 2 * conf.getFloat("map.output.growth.factor",
1.0) / numReduces
where totalInputSize is the size of all the maps inputs for the given job.
To start a new task,
newTaskAllocation + (sum over running tasks of (1.0 - done) * allocation) >=
free disk * conf.getFloat("mapred.max.scratch.allocation", 0.90);
So in English, we will model the expected sizes of tasks and only task tasks
that should leave us a 10% margin. With:
map.output.growth.factor -- the relative size of the transient data relative to
the map inputs
mapred.max.scratch.allocation -- the maximum amount of our disk we want to
allocate to tasks.
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