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From "jiangyu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9143) updateCountForQuota method during EditlogTailer loadEdit can make SNN timeout very often
Date Fri, 25 Sep 2015 09:05:04 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9143?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14907833#comment-14907833

jiangyu commented on HDFS-9143:

It is easy to reproduce it,  you can use a mapreduce program to make dir , when you make over
one hundred million dirs, you can finding this situation every time. I only use 20 datanodes
to test it.

> updateCountForQuota method during EditlogTailer loadEdit can make SNN timeout very often

> -----------------------------------------------------------------------------------------
>                 Key: HDFS-9143
>                 URL: https://issues.apache.org/jira/browse/HDFS-9143
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.4.0, 2.6.0
>            Reporter: jiangyu
>            Priority: Minor
> I have seen many logs from datanodes in our cluster reporting socket timeout when sending
heartbeat or blockReceivedAndDeleted to Standby NameNode, but it never happen to Active NameNode.
> At first, i thought it maybe caused by Editlog Tailer fetch Editlog too much making full
gc, but after i watched the gc log, it is not. So i investigate the code path and log, find
it only take very few seconds for the SNN to fetch the journal and merge it. But when you
open the webpage of SNN during merge processing, it can not response  like stop the world
time of full GC, but there is no gc at that time. So i jstack SNN for some time, and finding
all the time consumed by updateCountForQuota method in FSImage.  
> The updateCountForQuota is called ervry time when loadEdits, it update the count of each
directory with quota in the namespace from ROOT, besides it hold the write lock of FSImage,
so every time when SNN merge the edit from JN, it is always making the stop world.  
> I don't think it is necessary for SNN to updateCountForQuota everytime when tail the
edit, when trasition to Active, it call updateCountForQuota and never missing any quota data.

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