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https://issues.apache.org/jira/browse/FLUME-3083?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15962474#comment-15962474
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Satoshi Iijima commented on FLUME-3083:
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[~eskrm],
I found a potential corner case for the patch.
When the tail file are truncated (deleted or archived to compressed file) and a
new file is generated, the new file can occasionally have the same inode as the
truncated file.
Furthermore, the new file can have the same file size as the truncated file and
the new file has not been written after that.
Even in this case, miss reading events can be possible.
The condition to check last modified time should be left and a new condition to
check position (file size) had better be added as the OR condition.
> Taildir source can miss events if last updated time in same second as file
> mtime
> --------------------------------------------------------------------------------
>
> Key: FLUME-3083
> URL: https://issues.apache.org/jira/browse/FLUME-3083
> Project: Flume
> Issue Type: Bug
> Components: Sinks+Sources
> Affects Versions: 1.7.0
> Reporter: eskrm
> Attachments: FLUME-3083-0.patch
>
>
> I suspect there is a scenario where the taildir source can miss reading
> events from a log file due to how the source determines whether a file has
> been updated. In ReliableTaildirEventReader:
> {code}
> boolean updated = tf.getLastUpdated() < f.lastModified()
> ...
> tf.setNeedTail(updated);
> {code}
> Consider this sequence of events from TaildirSource.process(). Assume they
> all happen within the same second and there is just a single log file.
> # Call ReliableTaildirEventReader.updateTailFiles()
> #* This call will set ReliableTaildirEventReader.updateTime to current time
> in milliseconds
> #* Assume the underlying file has not been updated within the last
> idleTimeout milliseconds
> # Due to idleness, the tail file's inode is added to TaildirSource.idleInodes
> in idleFileCheckerRunnable
> # tf.needTail is false. Skip reading file.
> # Underlying file is updated with events E1
> # TaildirSource.closeTailFiles()
> #* Call TaildirSource.tailFileProcess() before close to read any pending
> events
> #* Events E1 are read and processed
> #* Since events were read, call ReliableTaildirEventReader.commit() which
> updates the tail file's position and sets its last updated time to
> ReliableTaildirEventReader.updateTime from 1.a
> #* Close file
> # Events E2 are written to underlying file. File's modification time is in
> the same second as the tail file's last updated time.
> # Since the time returned by File.lastModified() is the mtime in seconds
> converted to milliseconds the file's last modified time is less than the tail
> file's last updated time and taildir won't reopen the file to read E2.
> #* This behaviour of File.lastModified() may be platform/jvm specific. I
> confirmed the behavior using OpenJDK 8 on Ubuntu precise.
> Can someone confirm this?
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