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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4103) Support O(1) snapshot creation
Date Thu, 20 Dec 2012 18:17:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4103?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13537224#comment-13537224
] 

Aaron T. Myers commented on HDFS-4103:
--------------------------------------

Could I please ask for a day or two to review this before it gets committed? I've been trying
to work my way through reviewing it, but as Suresh points out it is a very big/complex patch
and it's been updated daily the last few days. I assure you I'll be prompt with my feedback.
                
> 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,
h4103_20121219.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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