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From "Xuefu Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-2688) Need a way to run multiple data pipeline concurrently
Date Sun, 25 Jan 2015 15:20:34 GMT

    [ https://issues.apache.org/jira/browse/SPARK-2688?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14291134#comment-14291134
] 

Xuefu Zhang commented on SPARK-2688:
------------------------------------

I think SPARK-3622 is related to this JIRA but not exactly the same. This JIRA essentially
asks capability of executing a random DAG built of RDDs, while SPARK-3622 is requesting a
custom transformation that can take one input RDD and generates multiple output RDDs. HIve
on Spark projects needs this because HIve's map-side or reduce-side processing (which is translated
to Spark's map functions) generates multiple outputs in general. On this ground, SPARK-3622
is more important than SPARK-2688.

It's worth to mention that such a custom transformation can be used in building a random DAG.


> Need a way to run multiple data pipeline concurrently
> -----------------------------------------------------
>
>                 Key: SPARK-2688
>                 URL: https://issues.apache.org/jira/browse/SPARK-2688
>             Project: Spark
>          Issue Type: New Feature
>          Components: Spark Core
>    Affects Versions: 1.0.1
>            Reporter: Xuefu Zhang
>
> Suppose we want to do the following data processing: 
> {code}
> rdd1 -> rdd2 -> rdd3
>            | -> rdd4
>            | -> rdd5
>            \ -> rdd6
> {code}
> where -> represents a transformation. rdd3 to rrdd6 are all derived from an intermediate
rdd2. We use foreach(fn) with a dummy function to trigger the execution. However, rdd.foreach(fn)
only trigger pipeline rdd1 -> rdd2 -> rdd3. To make things worse, when we call rdd4.foreach(),
rdd2 will be recomputed. This is very inefficient. Ideally, we should be able to trigger the
execution the whole graph and reuse rdd2, but there doesn't seem to be a way doing so. Tez
already realized the importance of this (TEZ-391), so I think Spark should provide this too.
> This is required for Hive to support multi-insert queries. HIVE-7292.



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