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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1719) Improve the utilization of shuffle copier threads
Date Thu, 16 Aug 2007 06:13:30 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-1719?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Devaraj Das updated HADOOP-1719:

    Attachment: 1719.patch

This patch addresses the issue. It also adds another check to the 'busy' logic. The check
being whether #uniqueHosts < #copiers, and if so conclude we are not busy enough. The logic
is that we fetch only one map output at a time from any given host and uniqueHosts keep a
track of that. As soon as we add a host to uniqueHosts, a 'copy' from that is scheduled as
well. Thus, when the size of uniqueHosts is >= numCopiers, it means that all copiers are
busy. Although the converse is not true (e.g. in the case where we have more copiers than
the number of hosts in the cluster), but it should generally be useful to do this check.

> Improve the utilization of shuffle copier threads
> -------------------------------------------------
>                 Key: HADOOP-1719
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1719
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: mapred
>            Reporter: Devaraj Das
>            Assignee: Devaraj Das
>             Fix For: 0.15.0
>         Attachments: 1719.patch
> In the current design, the scheduling of copies is done and the scheduler (the main loop
in fetchOutputs) won't schedule anything until it hears back from at least one of the copier
threads. Due to this, the main loop won't query the TaskTracker asking for new map locations
and may not be using all the copiers effectively. This may not be an issue for small-sized
map outputs, where at steady state, the frequency of such notifications is frequent.
> Ideally, we should schedule all what we can, and, depending on how busy we currently
are, query the tasktracker for more map locations.

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