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https://issues.apache.org/jira/browse/MAPREDUCE-7101?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16510203#comment-16510203
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Arun Suresh commented on MAPREDUCE-7101:
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Thanks [~tmarquardt].
The patch looks good to me. +1 The comment describing the new field in
JHAdminConfig is wrong - minor thing I can fix before committing.
Given that this patch retains the default behavior, and specific cloud
deployments can choose to always scan.
Maybe a pluggable FS specific scan is probably a better long term solution, but
I agree with [~leftnoteasy] and [~rohithsharma] that we should go ahead with
the approach in this patch to unblock.
> Revisit behavior of JHS scan file behavior
> ------------------------------------------
>
> 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
>
>
> 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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