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https://issues.apache.org/jira/browse/MAPREDUCE-6680?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15246699#comment-15246699
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Junping Du commented on MAPREDUCE-6680:
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bq. we can record latest scanning time on userDir as T2, and we scan the list
of directory in case: (T1 != T3) or (T1 = T3 but T1.toSeconds = T2.toSeconds),
that can get rid of skip problem and not involve many unnecessary scan - given
the chance file update happen at the same second with scan time is very low
(scan interval is default to be 3 minutes).
Another possibility is T1 (X second Y millisecond) and T3 (X second Z
millisecond) is cast to second (X+1) in FS. To address this, we need to check
(T1 != T3) or (T1 == T3 but T1.toSeconds >= T2.toSeconds). Updated this in v3
patch.
> JHS UserLogDir scan algorithm sometime could skip directory with update in
> CloudFS (Azure FileSystem, S3, etc.)
> ---------------------------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-6680
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6680
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: jobhistoryserver
> Reporter: Junping Du
> Assignee: Junping Du
> Attachments: MAPREDUCE-6680-v2.patch, MAPREDUCE-6680-v3.patch,
> MAPREDUCE-6680.patch
>
>
> In our cluster based on a Cloud FileSystem, we notice JHS sometimes could
> skip directory with .jhist file in scanning.
> The behavior is like:
> First round scan, doesn't found .jhist file:
> {noformat}
> 16/04/13 11:14:34 DEBUG azure.NativeAzureFileSystem: Found path as a
> directory with 6 files in it.
> 16/04/13 11:14:34 DEBUG hs.HistoryFileManager: Found 0 files
> ...
> {noformat}
> Then, we see "Scan not needed of ..." for the same directory every 3 minutes
> until application failed as timeout.
> From our analysis, we found the root cause is: most of Cloud File System
> (Azure FS, S3, etc.) is truncating file/directory modification time to
> seconds instead of milliseconds - which could due to limit of http protocol
> (from discussion at:
> https://forums.aws.amazon.com/thread.jspa?messageID=476615).
> So if the time sequence is happen to be: latest non .jhist file modification
> on directory happens at T1, directory scanning happens at T2, .jhist file
> added to directory at T3. If we have {{T1< T2 < T3}} and T1 is equal to T3
> after truncating to seconds, this issue could appear.
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