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From "Xuefu Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-3621) Provide a way to broadcast an RDD (instead of just a variable made of the RDD) so that a job can access
Date Sun, 25 Jan 2015 15:33:34 GMT

    [ https://issues.apache.org/jira/browse/SPARK-3621?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14291145#comment-14291145
] 

Xuefu Zhang commented on SPARK-3621:
------------------------------------

I'm not sure if I agree that this is "not a problem". To broadcast is to make certain dataset
available to all nodes in the cluster. Existing broadcast functionality is limited to broadcast
data in the driver, while this improvement requests that datasets, which already exists in
the cluster, be broadcast to all nodes without requiring shipping that dataset from the cluster
to the driver and then to all nodes in the cluster again.

Improvement is never a problem if we are not open to it. If for some reason this cannot be
done, we need to understand the reason.

> Provide a way to broadcast an RDD (instead of just a variable made of the RDD) so that
a job can access
> -------------------------------------------------------------------------------------------------------
>
>                 Key: SPARK-3621
>                 URL: https://issues.apache.org/jira/browse/SPARK-3621
>             Project: Spark
>          Issue Type: Improvement
>          Components: Spark Core
>    Affects Versions: 1.0.0, 1.1.0
>            Reporter: Xuefu Zhang
>
> In some cases, such as Hive's way of doing map-side join, it would be benefcial to allow
client program to broadcast RDDs rather than just variables made of these RDDs. Broadcasting
a variable made of RDDs requires all RDD data be collected to the driver and that the variable
be shipped to the cluster after being made. It would be more performing if driver just broadcasts
the RDDs and uses the corresponding data in jobs (such building hashmaps at executors).
> Tez has a broadcast edge which can ship data from previous stage to the next stage, which
doesn't require driver side processing.



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