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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4103) Support O(1) snapshot creation
Date Thu, 20 Dec 2012 07:35:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4103?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13536837#comment-13536837
] 

Tsz Wo (Nicholas), SZE commented on HDFS-4103:
----------------------------------------------

> 5. FSDirectory.java - replaceSelf4INodeDirectory() calls should be moved to INodeDirectoryWithQuota.setQuota()

I tried to move the call to setQuota() but it complicates the logic since FSDirectory.unprotectedSetQuota(..)
return null if nothing is changed; otherwise, return the inode (or the new inode.)  It needs
additional check if the call is moved to setQuota().
                
> Support O(1) snapshot creation
> ------------------------------
>
>                 Key: HDFS-4103
>                 URL: https://issues.apache.org/jira/browse/HDFS-4103
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>    Affects Versions: Snapshot (HDFS-2802)
>            Reporter: Tsz Wo (Nicholas), SZE
>            Assignee: Tsz Wo (Nicholas), SZE
>         Attachments: h4103_20121129.patch, h4103_20121202b.patch, h4103_20121202.patch,
h4103_20121209b.patch, h4103_20121209.patch, h4103_20121210b.patch, h4103_20121210.patch,
h4103_20121211.patch, h4103_20121212b.patch, h4103_20121212.patch, h4103_20121213.patch, h4103_20121215b.patch,
h4103_20121215.patch, h4103_20121216.patch, h4103_20121217b.patch, h4103_20121217.patch, h4103_20121218.patch
>
>
> In our first snapshot implementation, snapshot creation runs in O(N) and occupies O(N)
memory space, where N = # files + # directories + # symlinks in the snapshot.  The advantages
of the implementation are that there is no additional cost for the modifications after snapshots
are created, and it leads to a simple implementation.
> In this JIRA, we optimize snapshot creation to O(1) although it introduces additional
cost in the modifications after snapshots are created.  Note that the INode is given as an
assumption, otherwise, there is a non-constant cost to find the INode.

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