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From "Gabriel Reid (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CRUNCH-218) Add new Target.WriteMode to skip the write and continue pipeline if an output target exists
Date Thu, 13 Jun 2013 11:45:20 GMT

    [ https://issues.apache.org/jira/browse/CRUNCH-218?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13682143#comment-13682143
] 

Gabriel Reid commented on CRUNCH-218:
-------------------------------------

Ok, so the actual use case is the union of what I was talking about and what Josh's patch
does :-)

Like I said before, I definitely like the idea of both of these things, but I do think that
we need to have a way of saying that we want to overwrite something that has been written
in checkpoint mode previously. I'm thinking that this could either be done automatically,
by checking the creation time of the data that is used to create the checkpointed data, or
by having some kind of run mode to force overwriting checkpointed data. Or maybe we shouldn't
worry about that, and just advise extra caution for stale data when writing in checkpoint
mode.


                
> Add new Target.WriteMode to skip the write and continue pipeline if an output target
exists
> -------------------------------------------------------------------------------------------
>
>                 Key: CRUNCH-218
>                 URL: https://issues.apache.org/jira/browse/CRUNCH-218
>             Project: Crunch
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 0.6.0
>            Reporter: Dave Beech
>            Assignee: Josh Wills
>            Priority: Minor
>         Attachments: CRUNCH-218b.patch, CRUNCH-218.patch
>
>
> Quite often I write pipelines which persist data to the filesystem midway through the
process, and then carry on doing further work. 
> If this intermediate data is already present, I think it would be good if I could set
a write mode which skips over this first half of processing. This way I'd avoid running jobs
unnecessarily and wasting cluster resources regenerating data I already have. 
> Example:
> PCollection<B> inter = pipeline.read(source).parallelDo(something).parallelDo(somethingElse);
> inter.write(At.sequenceFile('output'), WriteMode.SKIP_IF_EXISTS);
> PCollection<C> final = inter.parallelDo(moreWork);
>  

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