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https://issues.apache.org/jira/browse/PIG-102?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12577018#action_12577018
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Benjamin Reed commented on PIG-102:
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In Hadoop, if you use local instead of an HDFS namenode as the file system, the
local files must be shared.
Pig allows a mix. if you are running with HDFS and you want to use local files,
you can specify a file: prefix to your files and the local file will be
transferred to HDFS before (or after depending on the context) the job runs. If
you throw a shared file system into the picture, you may want a mix. Since the
shared file system is treated as a local FS you have the option of copying or
not. Copying will give you more scalability. Not copying reduces latency
(sometimes).
> Dont copy to DFS if source filesystem marked as shared
> ------------------------------------------------------
>
> Key: PIG-102
> URL: https://issues.apache.org/jira/browse/PIG-102
> Project: Pig
> Issue Type: New Feature
> Components: impl
> Environment: Installations with shared folders on all nodes (eg NFS)
> Reporter: Craig Macdonald
> Attachments: shared.patch
>
>
> I've been playing with Pig using three setups:
> (a) local
> (b) hadoop mapred with hdfs
> (c) hadoop mapred with file:///path/to/shared/fs as the default file system
> In our local setup, various NFS filesystems are shared between all machines
> (including mapred nodes) eg /users, /local
> I would like Pig to note when input files are in a file:// directory that has
> been marked as shared, and hence not copy it to DFS.
> Similarly, the Torque PBS resource manager has a usecp directive, which notes
> when a filesystem location is shared between all nodes, (and hence scp is not
> needed, cp alone can be used). See
> http://www.clusterresources.com/wiki/doku.php?id=torque:6.2_nfs_and_other_networked_filesystems
> It would be good to have a configurable setting in Pig that says when a
> filesystem is shared, and hence no copying between file:// and hdfs:// is
> needed.
> An example in our setup might be:
> sharedFS file:///local/
> sharedFS file:///users/
> if commands should be used.
> This command should be used with care. Obviously if you have 1000 nodes all
> accessing a shared file in NFS, then it would have been better to "hadoopify"
> the file.
> The likely area of code to patch is
> src/org/apache/pig/impl/io/FileLocalizer.java hadoopify(String, PigContext)
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