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From "Gabriel Reid (JIRA)" <>
Subject [jira] [Commented] (CRUNCH-57) Add a length function to PCollection
Date Fri, 14 Sep 2012 08:05:08 GMT


Gabriel Reid commented on CRUNCH-57:

@Rahul, I don't really think that this is a situation that we need to overly optimize for
right now, and I definitely wouldn't say that we're losing what Hadoop can do for us out of
the box. I think that CPU usage will only be slightly lowered by making use of WritableComparable,
as the main objective here is to minimize the amount of data being sent to the reducer. Additionally,
the current implementation makes use of a Combiner, so it's likely that it'll be even more
successful in minimizing the size of the shuffle.

In any case, I think we're going pretty far outside the scope of this particular JIRA issue,
so it's probably best to continue this discussion on crunch-dev or a different JIRA issue.

> Add a length function to PCollection
> ------------------------------------
>                 Key: CRUNCH-57
>                 URL:
>             Project: Crunch
>          Issue Type: New Feature
>          Components: Core
>    Affects Versions: 0.3.0
>            Reporter: Kiyan Ahmadizadeh
>            Assignee: Josh Wills
>         Attachments: CRUNCH-57.patch, CRUNCH-57.patch, MinMaxFn.patch, minver2.patch
> Sometimes it's useful and interesting to compute the number of elements in a PCollection.
> For example, suppose there was an initial PCollection that was then filtered into another.
 If I'm interested in how many elements of the original PCollection matched the filter, I'll
have to write extra code to compute this.
> PCollections should have a length method that, when called, computes the number of elements
in the PCollection and returns the result. 

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