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Date: Thu, 17 Sep 2009 01:02:01 -0700 (PDT)
From: "Arun C Murthy (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-4952) Improved files system interface for
 the application writer.
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    [ https://issues.apache.org/jira/browse/HADOOP-4952?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12756405#action_12756405 ] 

Arun C Murthy commented on HADOOP-4952:
---------------------------------------

Ok, I finally got around to looking at this jira...

Given the discussion around the 2 options in HADOOP-6223 I'm assuming this patch goes for a less ambitious change to get in FileContext before the feature-freeze since we can't quite seem to agree on the newer file-system interface for file-system implementers?

> Improved files system interface for the application writer.
> -----------------------------------------------------------
>
>                 Key: HADOOP-4952
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4952
>             Project: Hadoop Common
>          Issue Type: Improvement
>    Affects Versions: 0.21.0
>            Reporter: Sanjay Radia
>            Assignee: Sanjay Radia
>         Attachments: FileContext-common10.patch, FileContext-common11.patch, FileContext-common12.patch, FileContext-common13.patch, FileContext-common14.patch, FileContext-common16.patch, FileContext-common18.patch, FileContext-common19.patch, FileContext-common21.patch, FileContext-common22.patch, FileContext-hdfs10.patch, FileContext-hdfs11.patch, FileContext3.patch, FileContext5.patch, FileContext6.patch, FileContext7.patch, FileContext9.patch, Files.java, Files.java, FilesContext1.patch, FilesContext2.patch
>
>
> Currently the FIleSystem interface serves two purposes:
> - an application writer's interface for using the Hadoop file system
> - a file system implementer's interface (e.g. hdfs, local file system, kfs, etc)
> This Jira proposes that we provide a simpler interfaces for the application writer and leave the FilsSystem  interface for the implementer of a filesystem.
> - Filesystem interface  has a  confusing set of methods for the application writer
> - We could make it easier to take advantage of the URI file naming
> ** Current approach is to get FileSystem instance by supplying the URI and then access that name space. It is consistent for the FileSystem instance to not accept URIs for other schemes, but we can do better.
> ** The special copyFromLocalFIle can be generalized as a  copyFile where the src or target can be generalized to any URI, including the local one.
> ** The proposed scheme (below) simplifies this.
> -	The client side config can be simplified. 
> ** New config() by default uses the default config. Since this is the common usage pattern, one should not need to always pass the config as a parameter when accessing the file system.  
> -	
> ** It does not handle multiple file systems too well. Today a site.xml is derived from a single Hadoop cluster. This does not make sense for multiple Hadoop clusters which may have different defaults.
> ** Further one should need very little to configure the client side:
> *** Default files system.
> *** Block size 
> *** Replication factor
> *** Scheme to class mapping
> ** It should be possible to take Blocksize and replication factors defaults from the target file system, rather then the client size config.  I am not suggesting we don't allow setting client side defaults, but most clients do not care and would find it simpler to take the defaults for their systems  from the target file system. 

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