[jira] Created: (MAPREDUCE-1266) Allow heartbeat interval smaller than 3 seconds for tiny clusters

["Todd Lipcon (JIRA)" <ji...@apache.org>]

Allow heartbeat interval smaller than 3 seconds for tiny clusters
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                 Key: MAPREDUCE-1266
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1266
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
          Components: jobtracker, task, tasktracker
    Affects Versions: 0.22.0
            Reporter: Todd Lipcon
            Priority: Minor


For small clusters, the heartbeat interval has a large effect on job latency. This is especially true on pseudo-distributed or other "tiny" (<5 nodes) clusters. It's not a big deal for production, but new users would have a happier first experience if Hadoop seemed snappier.

I'd like to change the minimum heartbeat interval from 3.0 seconds to perhaps 0.5 seconds (but have it governed by an undocumented config parameter in case people don't like this change). The cluster size-based ramp up of interval will maintain the current scalable behavior for large clusters with no negative effect.

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