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https://issues.apache.org/jira/browse/HDFS-3154?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13238868#comment-13238868
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Colin Patrick McCabe commented on HDFS-3154:
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I am aware of at least two "filesystems" (in the loose sense of the word) that
have immutable files. One is Venti from Plan9, and the other is git, by Linus
Torvalds. Both of them are significantly simpler because of their invariant
that files cannot change. However, both of them are append-only, meaning that
files can never be deleted. This seems unsuitable for the HDFS use case, and
in fact, I see no reason to believe that having some, but not all, files be
immutable would provide any benefit.
Can you list the concrete benefits you think would come from having some, but
not all, files be immutable? The linked email thread does not list anything
specific.
> 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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