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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6784) Avoid rescan twice in HDFS CacheReplicationMonitor for one FS Op if it calls setNeedsRescan multiple times.
Date Wed, 30 Jul 2014 16:28:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6784?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14079457#comment-14079457
] 

Hadoop QA commented on HDFS-6784:
---------------------------------

{color:red}-1 overall{color}.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12658640/HDFS-6784.001.patch
  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
tests.
                        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:green}+1 core tests{color}.  The patch passed 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/7498//testReport/
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/7498//console

This message is automatically generated.

> Avoid rescan twice in HDFS CacheReplicationMonitor for one FS Op if it calls setNeedsRescan
multiple times.
> -----------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-6784
>                 URL: https://issues.apache.org/jira/browse/HDFS-6784
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: caching
>    Affects Versions: 3.0.0
>            Reporter: Yi Liu
>            Assignee: Yi Liu
>         Attachments: HDFS-6784.001.patch
>
>
> In HDFS CacheReplicationMonitor,  rescan is expensive. Sometimes, {{setNeedsRescan}}
is called multiple times, for example, in FSNamesystem#modifyCacheDirective, there are 3 times.
In monitor thread of CacheReplicationMonitor, if it checks {{needsRescan}} is true, rescan
will happen, but {{needsRescan}} is set to false before real scan. Meanwhile, the 2nd or 3rd
time {{setNeedsResacn}} may set {{needsRescan}} to true. So after the scan finish, in next
loop, a new rescan will be triggered, that's not necessary at all and inefficient for rescan
twice. 



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