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https://issues.apache.org/jira/browse/HDFS-14276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16768627#comment-16768627
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Erik Krogen commented on HDFS-14276:
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Hey [~jojochuang], great find, thanks for reporting. Do you have new profiler
results after your patch?
More generally, regarding high CPU usage at idle, I have one idea for reducing
this. When a cluster is heavily loaded, it makes sense to reduce the edit tail
period as low as possible to keep the observer in sync with the active. But
when a cluster or idle or lightly loaded, there is no need for this. Perhaps we
can add some logic to decrease the edit tail frequency when the
Observer/Standby get empty responses from the JNs.
> [SBN read] Reduce tailing overhead
> ----------------------------------
>
> Key: HDFS-14276
> URL: https://issues.apache.org/jira/browse/HDFS-14276
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: ha, namenode
> Affects Versions: 3.3.0
> Environment: Hardware: 4-node cluster, each node has 4 core, Xeon
> 2.5Ghz, 25GB memory.
> Software: CentOS 7.4, CDH 6.0 + Consistent Reads from Standby, Kerberos, SSL,
> RPC encryption + Data Transfer Encryption.
> Reporter: Wei-Chiu Chuang
> Assignee: Wei-Chiu Chuang
> Priority: Major
> Attachments: HDFS-14276.000.patch, Screen Shot 2019-02-12 at 10.51.41
> PM.png
>
>
> When Observer sets {{dfs.ha.tail-edits.period}} = {{0ms}}, it tails edit log
> continuously in order to fetch the latest edits, but there is a lot of
> overhead in doing so.
> Critically, edit log tailer should _not_ update NameDirSize metric every
> time. It has nothing to do with fetching edits, and it involves lots of
> directory space calculation.
> Profiler suggests a non-trivial chunk of time is spent for nothing.
> Other than this, the biggest overhead is in the communication to
> serialize/deserialize messages to/from JNs. I am looking for ways to reduce
> the cost because it's burning 30% of my CPU time even when the cluster is
> idle.
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