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https://issues.apache.org/jira/browse/HDFS-3154?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13240244#comment-13240244
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M. C. Srivas commented on HDFS-3154:
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Ok, so the Andrew File System, from which Ceph draws a lot of inspiration, had
extensive client-side caching, and snapshots and mirrors. Plus the files were
100% mutable with stronger consistency semantics than NFS. And unlike Ceph and
more like HDFS, AFS ran on the local file system that came bundled with the
operating system.
So it is not hard to implement. The source code for AFS is out there in public
domain.
Making every file immutable introduces more complications for the users of
HDFS. It may simplify some things for the engineers developing it. But the
users have to deal with it on a daily basis. I'd rather that the engineers
solve the hard problems and provide simplicity to their users.
I suspect underlying all this is a use-case that is in the back of people's
minds, for which one solution might involve making every file permanently
immutable. It would be beneficial to illustrate the use-case and discuss.
> 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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