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https://issues.apache.org/jira/browse/HDFS-15486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17423078#comment-17423078
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Yiqun Lin commented on HDFS-15486:
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Asked by [~yuanbo] offline that if there is the patch for this JIRA, I have
attached the draft patch for this JIRA, this patch already applied in our
internal hadoop version and executed well in our production environment. It
can increased the RPC throughout for NameNode.
> Costly sendResponse operation slows down async editlog handling
> ---------------------------------------------------------------
>
> Key: HDFS-15486
> URL: https://issues.apache.org/jira/browse/HDFS-15486
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 2.7.0
> Reporter: Yiqun Lin
> Priority: Major
> Attachments: Async-profile-(2).jpg, async-profile-(1).jpg
>
>
> When our cluster NameNode in a very high load, we find it often stuck in
> Async-editlog handling.
> We use async-profile tool to get the flamegraph.
> !Async-profile-(2).jpg!
> This happened in that async editlog thread consumes Edit from the queue and
> triggers the sendResponse call.
> But here the sendResponse call is a little expensive since our cluster
> enabled the security env and will do some encode operations when doing the
> return response operation.
> We often catch some moments of costly sendResponse operation when rpc call
> queue is fulled.
> !async-profile-(1).jpg!
> Slowness on consuming Edit in async editlog will make Edit pending Queue
> easily become the fulled state, then block its enqueue operation that is
> invoked in writeLock type methods in FSNamesystem class.
> Here the enhancement is that we can use multiple thread to parallel execute
> sendResponse call. sendResponse doesn't need use the write lock to do
> protection, so this change is safe.
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