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https://issues.apache.org/jira/browse/HDFS-2486?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andrew Wang updated HDFS-2486:
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Fix Version/s: (was: 3.0.0)
2.7.0
I merged this down to branch-2 to make a cherry-pick cleaner.
> Review issues with UnderReplicatedBlocks
> ----------------------------------------
>
> Key: HDFS-2486
> URL: https://issues.apache.org/jira/browse/HDFS-2486
> Project: Hadoop HDFS
> Issue Type: Task
> Components: namenode
> Affects Versions: 0.23.0
> Reporter: Steve Loughran
> Assignee: Uma Maheswara Rao G
> Priority: Minor
> Fix For: 2.7.0
>
> Attachments: HDFS-2486.patch
>
>
> Here are some things I've noted in the UnderReplicatedBlocks class that
> someone else should review and consider if the code is correct. If not, they
> are easy to fix.
> remove(Block block, int priLevel) is not synchronized, and as the inner
> classes are not, there is a risk of race conditions there.
> some of the code assumes that getPriority can return the value LEVEL, and if
> so does not attempt to queue the blocks. As this return value is not
> currently possible, those checks can be removed.
> The queue gives priority to blocks whose replication count is less than a
> third of its expected count over those that are "normally under replicated".
> While this is good for ensuring that files scheduled for large replication
> are replicated fast, it may not be the best strategy for maintaining data
> integrity. For that it may be better to give whichever blocks have only two
> replicas priority over blocks that may, for example, already have 3 out of 10
> copies in the filesystem.
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