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From "Olga Natkovich (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-872) use distributed cache for the replicated data set in FR join
Date Wed, 18 Nov 2009 01:09:39 GMT

    [ https://issues.apache.org/jira/browse/PIG-872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12779238#action_12779238
] 

Olga Natkovich commented on PIG-872:
------------------------------------

Patch looks good. A couple of comments:

(1) Looks like the newly added test just have a plain replicated join. I think this is already
covered in TestFRJoin.java.
(2) JobControlCompiler.java" 943 lines: the comment says that the fragmented input is usually
null and that it is the first one. Would it be more clear if we just started with the second
file and did not have to check for null every time since null in any other position should
be treated as error.

> use distributed cache for the replicated data set in FR join
> ------------------------------------------------------------
>
>                 Key: PIG-872
>                 URL: https://issues.apache.org/jira/browse/PIG-872
>             Project: Pig
>          Issue Type: Improvement
>            Reporter: Olga Natkovich
>            Assignee: Sriranjan Manjunath
>         Attachments: PIG_872.patch
>
>
> Currently, the replicated file is read directly from DFS by all maps. If the number of
the concurrent maps is huge, we can overwhelm the NameNode with open calls.
> Using distributed cache will address the issue and might also give a performance boost
since the file will be copied locally once and the reused by all tasks running on the same
machine.
> The basic approach would be to use cacheArchive to place the file into the cache on the
frontend and on the backend, the tasks would need to refer to the data using path from the
cache.
> Note that cacheArchive does not work in Hadoop local mode. (Not a problem for us right
now as we don't use it.)

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