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https://issues.apache.org/jira/browse/HDFS-14497?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16841136#comment-16841136
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Wei-Chiu Chuang commented on HDFS-14497:
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How long does it take to metasave? IIRC it's around several minutes range for
large clusters.
I don't think switching to read lock would help much. I've seen read-only RPCs
holding lock for too long and cause failover. (e.g. deleteSnapshot)
> 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
>
> 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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