[jira] [Created] (HDFS-14276) [SBN read] Reduce tailing overhead

["Wei-Chiu Chuang (JIRA)" <ji...@apache.org>]

Wei-Chiu Chuang created HDFS-14276:
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             Summary: [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
         Attachments: 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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