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https://issues.apache.org/jira/browse/HDFS-5153?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Arpit Agarwal updated HDFS-5153:
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Issue Type: Improvement (was: Bug)
> Datanode should send block reports for each storage in a separate message
> -------------------------------------------------------------------------
>
> Key: HDFS-5153
> URL: https://issues.apache.org/jira/browse/HDFS-5153
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Affects Versions: 3.0.0
> Reporter: Arpit Agarwal
> Assignee: Arpit Agarwal
> Attachments: HDFS-5153.01.patch, HDFS-5153.03.patch,
> HDFS-5153.03b.patch, HDFS-5153.04.patch, HDFS-5153.05.patch
>
>
> When the number of blocks on the DataNode grows large we start running into a
> few issues:
> # Block reports take a long time to process on the NameNode. In testing we
> have seen that a block report with 6 Million blocks takes close to one second
> to process on the NameNode. The NameSystem write lock is held during this
> time.
> # We start hitting the default protobuf message limit of 64MB somewhere
> around 10 Million blocks. While we can increase the message size limit it
> already takes over 7 seconds to serialize/unserialize a block report of this
> size.
> HDFS-2832 has introduced the concept of a DataNode as a collection of
> storages i.e. the NameNode is aware of all the volumes (storage directories)
> attached to a given DataNode. This makes it easy to split block reports from
> the DN by sending one report per storage directory to mitigate the above
> problems.
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