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https://issues.apache.org/jira/browse/HDFS-14497?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16846725#comment-16846725
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Wei-Chiu Chuang commented on HDFS-14497:
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bq. I agree that it could not solve problem completely, however it may improve
something, for instance, heartbeat could be process by namenode when we switch
to read lock, especially it could be very useful if there no lifeline
installation.
Ok. That probably makes sense.
To be honest, I don't see very large installation a lot -- typically just a few
hundred ~ 2000 nodes. I can believe NN should be more delicate for even larger
clusters.
> Write lock hold by metasave impact following RPC processing
> -----------------------------------------------------------
>
> Key: HDFS-14497
> URL: https://issues.apache.org/jira/browse/HDFS-14497
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Reporter: He Xiaoqiao
> Assignee: He Xiaoqiao
> Priority: Major
> Attachments: HDFS-14497.001.patch
>
>
> NameNode meta save hold global write lock currently, so following RPC r/w
> request or inner-thread of NameNode could be paused if they try to acquire
> global read/write lock and have to wait before metasave release it.
> I propose to change write lock to read lock and let some read request could
> be process normally. I think it could not change informations which meta save
> try to get if we try to open read request.
> Actually, we need ensure that there are only one thread to execute metaSave,
> otherwise, output streams could meet exception especially both streams hold
> the same file handle or some other same output stream.
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