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From "Andrzej Bialecki (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-490) Add ability to send "signals" to jobs and tasks
Date Sat, 16 Sep 2006 11:21:23 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-490?page=comments#action_12435209 ] 
            
Andrzej Bialecki  commented on HADOOP-490:
------------------------------------------

(Oops, I thought JIRA would include the link in the comment).

NUTCH-368 provides an implementation of a filesystem-based message queue system. This implementation
is not Nutch specific, and can be easily moved to Hadoop if users find it useful.

> Add ability to send "signals" to jobs and tasks
> -----------------------------------------------
>
>                 Key: HADOOP-490
>                 URL: http://issues.apache.org/jira/browse/HADOOP-490
>             Project: Hadoop
>          Issue Type: New Feature
>          Components: mapred
>    Affects Versions: 0.6.0
>            Reporter: Andrzej Bialecki 
>
> In some cases it would be useful to be able to "signal" a job and its tasks about some
external condition, or to broadcast a specific message to all tasks in a job. Currently we
can only send  a single pseudo-signal, that is to kill a job.
> Example 1: some jobs may be gracefully terminated even if they didn't complete all their
work, e.g. Fetcher in Nutch may be running for a very long time if it blocks on relatively
few sites left over from the fetchlist. In such case it would be very useful to send it a
message requesting that it discards the rest of its input and gracefully completes its map
tasks.
> Example 2: available bandwidth for fetching may be different at different times of day,
e.g. daytime vs. nighttime, or total external link usage by other applications. Fetcher jobs
often run for several hours. It would be good to be able to send a "signal" to the Fetcher
to throttle or un-throttle its bandwidth usage depending on external conditions.
> Job implementations could react to these messages either by implementing a method, or
by registering a listener, whichever seems more natural.
> I'm not quite sure how to go about implementing it, I guess this would have to be a part
of  TaskUmbilicalProtocol but my knowledge here is a bit fuzzy ... ;) Comments are welcome.

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