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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6766) optimize ack notify mechanism to avoid thundering herd issue
Date Tue, 29 Jul 2014 15:47:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14077854#comment-14077854

Hadoop QA commented on HDFS-6766:

{color:red}-1 overall{color}.  Here are the results of testing the latest attachment 
  against trunk revision .

    {color:green}+1 @author{color}.  The patch does not contain any @author tags.

    {color:red}-1 tests included{color}.  The patch doesn't appear to include any new or modified
                        Please justify why no new tests are needed for this patch.
                        Also please list what manual steps were performed to verify this patch.

    {color:green}+1 javac{color}.  The applied patch does not increase the total number of
javac compiler warnings.

    {color:green}+1 javadoc{color}.  There were no new javadoc warning messages.

    {color:green}+1 eclipse:eclipse{color}.  The patch built with eclipse:eclipse.

    {color:green}+1 findbugs{color}.  The patch does not introduce any new Findbugs (version
2.0.3) warnings.

    {color:green}+1 release audit{color}.  The applied patch does not increase the total number
of release audit warnings.

    {color:red}-1 core tests{color}.  The patch failed these unit tests in hadoop-hdfs-project/hadoop-hdfs:


    {color:green}+1 contrib tests{color}.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-HDFS-Build/7485//testReport/
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/7485//console

This message is automatically generated.

> optimize ack notify mechanism to avoid thundering herd issue
> ------------------------------------------------------------
>                 Key: HDFS-6766
>                 URL: https://issues.apache.org/jira/browse/HDFS-6766
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client
>    Affects Versions: 3.0.0
>            Reporter: Liang Xie
>            Assignee: Liang Xie
>         Attachments: HDFS-6766.txt
> Currently, DFSOutputStream uses wait/notifyAll to coordinate ack receiving and ack waiting,
> say there're 5 threads(t1,t2,t3,t4,t5) wait for ack seq no: 1,2,3,4,5, once the no. 1
ack arrived, the "notifyAll" be called, so t2/t3/t4/t5 could do nothing except wait again.
> we can rewrite it with Condition class, with a fair policy(fifo), we can just make t1
be notified, so a number of context switch be saved.
> It's possible more than one thread waiting on the same ack seq no(e.g. no more data be
written between two flush operations), so once it happened, we need to notify those threads,
so i introduced a set to remember this seq no.
> In a simple HBase ycsb testing, the context switch number per second was reduced about
15%, and reduced sys cpu% about 6%(My HBase has new write model patch, i think the benefit
will be higher if w/o it)

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