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From "Hari Mankude (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3154) Add a notion of immutable/mutable files
Date Tue, 27 Mar 2012 18:27:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3154?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13239790#comment-13239790

Hari Mankude commented on HDFS-3154:

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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