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From "Josh Wills (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CRUNCH-128) Allow one stage of an MR pipeline to depend on another target being created
Date Sun, 16 Dec 2012 21:16:12 GMT

    [ https://issues.apache.org/jira/browse/CRUNCH-128?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13533522#comment-13533522
] 

Josh Wills commented on CRUNCH-128:
-----------------------------------

Yeah, let me see if I can wire it up right quick. It might be even better if I called it "advancedParallelDo"
or some such thing to keep it out of auto-complete.
                
> 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
>
>
> 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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