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https://issues.apache.org/jira/browse/HDFS-5064?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13924521#comment-13924521
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Hudson commented on HDFS-5064:
------------------------------
SUCCESS: Integrated in Hadoop-trunk-Commit #5286 (See
[https://builds.apache.org/job/Hadoop-trunk-Commit/5286/])
HDFS-5064. Standby checkpoints should not block concurrent readers. Contributed
by Aaron Twining Myers. (wang:
http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1575448)
* /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
*
/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImage.java
*
/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
*
/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystemLock.java
*
/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NNStorage.java
*
/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/StandbyCheckpointer.java
*
/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/RwLock.java
*
/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestStandbyCheckpoints.java
> Standby checkpoints should not block concurrent readers
> -------------------------------------------------------
>
> Key: HDFS-5064
> URL: https://issues.apache.org/jira/browse/HDFS-5064
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: ha, namenode
> Affects Versions: 2.3.0
> Reporter: Aaron T. Myers
> Assignee: Aaron T. Myers
> Fix For: 2.4.0
>
> Attachments: HDFS-5064.patch, HDFS-5064.patch
>
>
> We've observed an issue which causes fetches of the {{/jmx}} page of the NN
> to take a long time to load when the standby is in the process of creating a
> checkpoint.
> Even though both creating the checkpoint and gathering the statistics for
> {{/jmx}} take only the FSNS read lock, the issue is that since the FSNS uses
> a _fair_ RW lock, a single writer attempting to get the lock will block all
> threads attempting to get only the read lock for the duration of the
> checkpoint. This will cause {{/jmx}}, and really any thread only attempting
> to get the read lock, to block for the duration of the checkpoint, even
> though they should be able to proceed concurrently with the checkpointing
> thread.
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