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Date: Wed, 10 Apr 2013 20:41:16 +0000 (UTC)
From: "Brandon Li (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12631775.1360608342450.145159.1365626476427@arcas>
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Subject: [jira] [Commented] (HDFS-4489) Use InodeID as as an identifier of a
 file in HDFS protocols and APIs
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    [ https://issues.apache.org/jira/browse/HDFS-4489?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13628217#comment-13628217 ] 

Brandon Li commented on HDFS-4489:
----------------------------------

{quote}I am not saying it is a showstopper. I just felt it should be given more thought. {quote}
In many cases, a trade-off is involved with the introduction of a new feature or enhancement. 
This JIRA was forked from HDFS-4258 and the discussion/experiment has been going on for more than 4 months. 

As shown in the theory analysis and experiment results, the memory overhead of this change is not significant. It doesn't seems to be worthwhile for now to complicate NameNode code to do the extra optimizations. 
                
> Use InodeID as as an identifier of a file in HDFS protocols and APIs
> --------------------------------------------------------------------
>
>                 Key: HDFS-4489
>                 URL: https://issues.apache.org/jira/browse/HDFS-4489
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>            Reporter: Brandon Li
>            Assignee: Brandon Li
>
> The benefit of using InodeID to uniquely identify a file can be multiple folds. Here are a few of them:
> 1. uniquely identify a file cross rename, related JIRAs include HDFS-4258, HDFS-4437.
> 2. modification checks in tools like distcp. Since a file could have been replaced or renamed to, the file name and size combination is no t reliable, but the combination of file id and size is unique.
> 3. id based protocol support (e.g., NFS)
> 4. to make the pluggable block placement policy use fileid instead of filename (HDFS-385).

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