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https://issues.apache.org/jira/browse/PIG-5071?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15730806#comment-15730806
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Daniel Dai commented on PIG-5071:
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Pig use JobControl to submit multiple jobs at a time, eg, A1+B1+C1+D1, and then
A2+B2+C2+D2. However, A1+B1+C1+D1 is treated as a unit, if B1 finishes earlier,
JobControl is not finishes and cannot proceed to next iteration. This is a
non-issue in Tez however, as Tez vertex run completely asynchronously.
> MapReduce concurrency Could Be Better
> -------------------------------------
>
> Key: PIG-5071
> URL: https://issues.apache.org/jira/browse/PIG-5071
> Project: Pig
> Issue Type: Wish
> Reporter: William Watson
>
> We have a job that launches, after optimization, about 20 MapReduce jobs.
> Some of these are quite long running and while pig does an okay job of
> running jobs concurrently, it could do better at least in this very specific
> case.
> The pig job can be divided up amongst 4 major sections like so:
> A1 -> A2 -> A3 -> A4 -> A
> B1 -> B2 -> B
> C1 -> C2 -> C3 -> C
> D1 -> D2 -> D3 -> D4 -> D
> and the sections are joined at the end:
> A + B -> AB
> AB + C -> ABC
> ABC + D -> ABCD
> In short, if C2 finishes very quickly, C3 won't be started until A2, B2, and
> D2 are all also complete. This is a problem if say, D2 takes an hour and
> there are unused cluster resources that could be made available to C3 (and by
> extension A3 and B3 if their prerequisites also finish before D2).
> One possible work around is to scale D2 better, but that's besides the point.
> I think pig is capable of knowing that the prerequisites are done for certain
> jobs, but since it only kicks off jobs in "phases", it won't kick off jobs as
> soon as possible.
> I've taken a look at the code and I'm having a hard time working out where
> the issue is or else I would be glad to contribute a patch.
> Is this a desirable feature and is this directly controlled by pig? If so,
> could someone help point me in the right direction so I can contribute a
> patch?
> Note: We can change this from a "wish" to an "improvement" if this feature is
> desired...
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