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From "Konstantin Boudnik (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1266) Allow heartbeat interval smaller than 3 seconds for tiny clusters
Date Sat, 05 Dec 2009 19:38:20 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12786470#action_12786470
] 

Konstantin Boudnik commented on MAPREDUCE-1266:
-----------------------------------------------

Here's an interesting though: why don't we throw some ergonomics into Hadoop's intellect?
If heartbeats seem to increase the latencies on small clusters then, perhaps, Hadoop can lower
it dynamically if a small cluster is 'detected'?

> Allow heartbeat interval smaller than 3 seconds for tiny clusters
> -----------------------------------------------------------------
>
>                 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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