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From "Matthias Friedrich (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CRUNCH-128) Allow one stage of an MR pipeline to depend on another target being created
Date Mon, 17 Dec 2012 14:56:32 GMT

    [ https://issues.apache.org/jira/browse/CRUNCH-128?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13533963#comment-13533963
] 

Matthias Friedrich commented on CRUNCH-128:
-------------------------------------------

I think I would have just added the two parallelDo() methods like Josh did in patch revision
aa73524. These two methods take additional parameters, so it should be clear to users that
they are dealing with a generalized parallelDo(). This is more difficult to infer from advancedParallelDo().
Also, my Eclipse version puts methods with shorter signatures at the top when auto-completing
while advancedParallelDo(). Anyway, this is a matter of taste.

>From the "keeping the interface small" point of view, I think those two extra methods
are warranted -- we need them, there's no way around it. We could remove the sample() and
sort() methods to make room ;-)

Regarding CrunchRuntimeException: How about moving it to the base package? Then we could still
use it without introducing cycles.
                
> Allow one stage of an MR pipeline to depend on another target being created
> ---------------------------------------------------------------------------
>
>                 Key: CRUNCH-128
>                 URL: https://issues.apache.org/jira/browse/CRUNCH-128
>             Project: Crunch
>          Issue Type: Improvement
>            Reporter: Josh Wills
>         Attachments: CheckpointingIT.java, CRUNCH-128.patch, CRUNCH-128v2.patch, CRUNCH-128-with-op.patch
>
>
> There are a couple of problems (e.g., mapside-joins, total orderings, etc.) where we
need to guarantee that one PCollection has been written to the FileSystem before another MapReduce
pipeline that depends on that file is allowed to run. This doesn't fit cleanly into the current
set of abstractions for Crunch, which is why we force pipelines to execute via the run command
to guarantee that the files have been created before the second stage is run.
> We should add the ability for a particular PCollection to require that a SourceTarget
instance has been created before it can be executed, and the planner should incorporate this
information into the MR pipeline planning process.

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