Review issues with UnderReplicatedBlocks
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Key: HDFS-2486
URL: https://issues.apache.org/jira/browse/HDFS-2486
Project: Hadoop HDFS
Issue Type: Task
Components: name-node
Affects Versions: 0.23.0
Reporter: Steve Loughran
Priority: Minor
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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