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https://issues.apache.org/jira/browse/HDFS-4103?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13537677#comment-13537677
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Tsz Wo (Nicholas), SZE commented on HDFS-4103:
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Aaron, below are my responses to your comments with some questions. I will
wait for your reply before making any change.
1. Where is commented code without explanation? Could you show me the line
numbers?
2. If the test fails, we may then enable the message and re-run the test. Is
there anything wrong?
3. We already have HDFS-4098 for append with snapshots.
4. I don't see why the symbol "====> <====" is better then "XXX".
5. Is this the same as #1?
6. Sure.
7. The method is short and simple enough to be understood. Don't you agree? I
think we are writing code but not a book for teaching Java.
8. It is only a unit test. The current code is good enough.
9. You may be right but (1) I don't think addressing it does not add any value
and (2) it was not added by the patch here.
10. testSnapshotPathINodesAfterModification(..) is current disabled.
11. How many? I only found two excluding tests.
12. Let's change it to "that".
13. You are right that these classes are generic but they are not yet ready to
be library code and I don't want other contributors to abuse them. Let's do it
later.
14. Thank you.
15. You seems don't like non-static inner classes? Is there a reason?
16. Filed HDFS-4330.
17. Sure.
> 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
> Fix For: Snapshot (HDFS-2802)
>
> 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, h4103_20121220.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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