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https://issues.apache.org/jira/browse/HDFS-2421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13434756#comment-13434756
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Suresh Srinivas commented on HDFS-2421:
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Jing, given the performance numbers you have posted for the map is being used
in a tight loop, I doubt if this makes such a big difference for the overall
NameNode performance.
Hairong or Weiyan, do you have any numbers to substantiate the improvement? BTW
we should create a separate jira to improve the get method which checks the map
entries two times, once with contains then to get.
> Improve the concurrency of SerialNumberMap in NameNode
> -------------------------------------------------------
>
> Key: HDFS-2421
> URL: https://issues.apache.org/jira/browse/HDFS-2421
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: name-node
> Reporter: Hairong Kuang
> Assignee: Weiyan Wang
> Fix For: 0.24.0
>
> Attachments: HDFS-2421.patch, performance_SerialNumberManager.png,
> TestSerialNumberManager.java
>
>
> After enabled permission checking in our HDFS test cluster, our benchmark
> observed a significant reduced concurrency in NameNode. Investigation showed
> that most threads were blocked at acquiring the lock of
> org.apache.hadoop.hdfs.server.namenode.SerialNumberManager$SerialNumberMap.
> We used concurrentHashMap to replace Hashmap + synchronized methods, which
> greatly improved the situation.
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