[jira] Updated: (PIG-1218) Use distributed cache to store samples

["Richard Ding (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/PIG-1218?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Richard Ding updated PIG-1218:
------------------------------

    Attachment: PIG-1218.patch

This patch uses Hadoop DistributedCache to cache the sample files used by order by and skewed join, as well as the side files used in FR join.

When a HDFS file is added to the DistributedCache,  Pig generates a symlink to the file and, at runtime, this symlink is used to open the file  from the local working directory of the task. To avoid symlink colision, instead of using file name, a symlink name is generated by using a combination of the hashcode of the file path and the current timestamp. 

The replication factor for the sample file in HDFS is not changed with this patch. The reasons are that we're not clear what's the right factor to increase, and the work to implement the change in Pig is not trivail. 



> Use distributed cache to store samples
> --------------------------------------
>
>                 Key: PIG-1218
>                 URL: https://issues.apache.org/jira/browse/PIG-1218
>             Project: Pig
>          Issue Type: Improvement
>            Reporter: Olga Natkovich
>            Assignee: Richard Ding
>             Fix For: 0.7.0
>
>         Attachments: PIG-1218.patch
>
>
> Currently, in the case of skew join and order by we use sample that is just written to the dfs (not distributed cache) and, as the result, get opened and copied around more than necessary. This impacts query performance and also places unnecesary load on the name node

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