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https://issues.apache.org/jira/browse/HDFS-4103?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13536803#comment-13536803
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Suresh Srinivas commented on HDFS-4103:
---------------------------------------
This is a long patch and a very laborious to review.
Here are the comments I have accumulated so far. I have few more files to
review:
# INode#save2Snapshot() - please add more javadoc to the method to indicate
"Inode is being modified. The previous version of the inode needs to be
recorded in the latest snapshot." It may also be good to call the method,
recordModification().
#* In a subsequent jira, do you think it is a good idea to have an interface
called SnapshotTracker/SnapshotRecorder in which we can have methods such as
save2Snapshot etc?
# INodeDirectory.java
#* "the latest snapshot has been taken" you mean "the latest snapshot +that+
has been taken"
#* getChild() does not use isLastINode parameter
# INodeDirectoryWithQuota#setQuota - @param names are incorrect
# FSDirectory#unprotectedDelete - Can you create a jira to ensure when a file
is deleted, if it exists no in the latest snapshot but much older snapshots,
the blocks are not deleted? This can be done in another jira. Also:
#* If the deleted file has 3 blocks and snapshotted file has first two blocks
only, do we delete the 3rd block? This can be addressed in another jira as well.
# FSDirectory.java - replaceSelf4INodeDirectory() calls should be moved to
INodeDirectoryWithQuota.setQuota()
# INodeDirectorySnapshot
#* format the #snapshotByNames javadoc comment
#* SnapshotDiff - please use <pre> and </pre> to ensure the javadoc is
readable. Consider making this static class by passing appropriate outer class
state to it.
> 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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