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Date: Thu, 22 Sep 2016 22:13:20 +0000 (UTC)
From: "Lei (Eddy) Xu (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12779186.1425417893000.643088.1474582400844@Atlassian.JIRA>
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References: <JIRA.12779186.1425417893000@Atlassian.JIRA> <JIRA.12779186.1425417893793@arcas>
Subject: [jira] [Commented] (HDFS-7878) API - expose an unique file
 identifier
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archived-at: Thu, 22 Sep 2016 22:13:23 -0000


    [ https://issues.apache.org/jira/browse/HDFS-7878?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15514629#comment-15514629 ] 

Lei (Eddy) Xu commented on HDFS-7878:
-------------------------------------

[~chris.douglas] Thanks a lot for working on it. 

I'd prefer to use {{FileStatus}} with {{file id}} instead a new {{FileHandler}} or {{InodeId}}.  As it is more familiar with the users, and if people want to use {{FileId}} alone to save memory (e.g., using in cache), they have the choice of using {{FileStatus#getFileId()}}.  I think it'd be easier to make this API be used by downstream projects. Additionally, {{InodeId}} looks implementation-specific to me, which makes this API not useful to or be supported natively by other backend (i.e., Azure or S3)?. One additional point is that {{stat(2)}} returns inode ({{stat.st_inode}}) as well, so it should not be too surprised for the end user.

And it might be worthwhile to take this chance to finally change {{FileStatus}} to be serializable for Protobuf (HDFS-6984) from Hadoop 3 and onward.  

Thanks.

> API - expose an unique file identifier
> --------------------------------------
>
>                 Key: HDFS-7878
>                 URL: https://issues.apache.org/jira/browse/HDFS-7878
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Sergey Shelukhin
>            Assignee: Sergey Shelukhin
>              Labels: BB2015-05-TBR
>         Attachments: HDFS-7878.01.patch, HDFS-7878.02.patch, HDFS-7878.03.patch, HDFS-7878.04.patch, HDFS-7878.05.patch, HDFS-7878.06.patch, HDFS-7878.patch
>
>
> See HDFS-487.
> Even though that is resolved as duplicate, the ID is actually not exposed by the JIRA it supposedly duplicates.
> INode ID for the file should be easy to expose; alternatively ID could be derived from block IDs, to account for appends...
> This is useful e.g. for cache key by file, to make sure cache stays correct when file is overwritten.


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