[jira] [Commented] (MAPREDUCE-7101) Add config parameter to allow JHS to alway scan user dir irrespective of modTime

["Hadoop QA (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAPREDUCE-7101?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16510369#comment-16510369 ] 

Hadoop QA commented on MAPREDUCE-7101:
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| (x) *{color:red}-1 overall{color}* |
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|| Vote || Subsystem || Runtime || Comment ||
| {color:blue}0{color} | {color:blue} reexec {color} | {color:blue} 11m 56s{color} | {color:blue} Docker mode activated. {color} |
| {color:red}-1{color} | {color:red} patch {color} | {color:red}  0m  6s{color} | {color:red} MAPREDUCE-7101 does not apply to trunk. Rebase required? Wrong Branch? See https://wiki.apache.org/hadoop/HowToContribute for help. {color} |
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|| Subsystem || Report/Notes ||
| Docker | Client=17.05.0-ce Server=17.05.0-ce Image:yetus/hadoop:abb62dd |
| JIRA Issue | MAPREDUCE-7101 |
| JIRA Patch URL | https://issues.apache.org/jira/secure/attachment/12927536/MAPREDUCE-7101.001.patch |
| Console output | https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/7440/console |
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> Add config parameter to allow JHS to alway scan user dir irrespective of modTime
> --------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-7101
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-7101
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>            Reporter: Wangda Tan
>            Assignee: Thomas Marquardt
>            Priority: Critical
>         Attachments: MAPREDUCE-7101.001.patch, MAPREDUCE-7101.001.patch
>
>
> Currently, the JHS scan directory if the modification of *directory* changed: 
> {code} 
>     public synchronized void scanIfNeeded(FileStatus fs) {
>       long newModTime = fs.getModificationTime();
>       if (modTime != newModTime) {
>         <... omitted some logics ...>
>         // reset scanTime before scanning happens
>         scanTime = System.currentTimeMillis();
>         Path p = fs.getPath();
>         try {
>           scanIntermediateDirectory(p);
> {code}
> This logic relies on an assumption that, the directory's modification time will be updated if a file got placed under the directory.
> However, the semantic of directory's modification time is not consistent in different FS implementations. For example, MAPREDUCE-6680 fixed some issues of truncated modification time. And HADOOP-12837 mentioned on S3, the directory's modification time is always 0.
> I think we need to revisit behavior of this logic to make it to more robustly work on different file systems.



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