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https://issues.apache.org/jira/browse/HDFS-3154?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13239790#comment-13239790
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Hari Mankude commented on HDFS-3154:
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bq. You can already do this. Create two users both in the "users" group. Have
the files owned by user #1 and put them in the "users" group. Then use mode
0640. Then user #2 can read the files, but not write them.
Immutable implies that file cannot be appended/truncated by anybody after the
file is finalized. I don't think permissions would be enough to guarantee
immutability. Generally guarantees of immutability has use cases in the
legal/SEC environments.
> Add a notion of immutable/mutable files
> ---------------------------------------
>
> Key: HDFS-3154
> URL: https://issues.apache.org/jira/browse/HDFS-3154
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: name-node
> Reporter: Tsz Wo (Nicholas), SZE
> Assignee: Tsz Wo (Nicholas), SZE
>
> The notion of immutable file is useful since it lets the system and tools
> optimize certain things as discussed in [this email
> thread|http://mail-archives.apache.org/mod_mbox/hadoop-hdfs-dev/201203.mbox/%3CCAPn_vTuZomPmBTypP8_1xTr49Sj0fy7Mjhik4DbcAA+BLH53=g...@mail.gmail.com%3E].
> Also, many applications require only immutable files. Here is a proposal:
> - Immutable files means that the file content is immutable. Operations such
> as append and truncate that change the file content are not allowed to act on
> immutable files. However, the meta data such as replication and permission
> of an immutable file can be updated. Immutable files can also be deleted or
> renamed.
> - Users have to pass immutable/mutable as a flag in file creation. This is
> an unmodifiable property of the created file.
> - If users want to change the data in an immutable file, the file could be
> copied to another file which is created as mutable.
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