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https://issues.apache.org/jira/browse/NIFI-4205?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16093091#comment-16093091
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ASF GitHub Bot commented on NIFI-4205:
--------------------------------------
Github user pvillard31 commented on the issue:
https://github.com/apache/nifi/pull/2021
Hi @ijokarumawak. I'm really not sure but I think that 'if' statement was
in case the file is rolling over and the new file has exactly the same content
as the one rolled over. In that case (I acknowledge that would be a very
strange edge case) we have:
``timestamp < file.lastModified() && length == file.length())``
In this case, the checksum would be the same and the boolean
``rolloverOccurred`` could be false. Again, that would be a really weird
situation and I'd say that this condition is not needed. Your change makes
sense to me especially with the issue you raised about duplicated data.
> TailFile can produce duplicated data when it wrongly assumes a file is rotated
> ------------------------------------------------------------------------------
>
> Key: NIFI-4205
> URL: https://issues.apache.org/jira/browse/NIFI-4205
> Project: Apache NiFi
> Issue Type: Bug
> Components: Extensions
> Affects Versions: 1.1.0
> Reporter: Koji Kawamura
> Assignee: Koji Kawamura
>
> TailFile checks whether a file being tailed is rotated by following lines of
> code, and if it determines so, it resets the reader and state for the file:
> https://github.com/apache/nifi/blob/master/nifi-nar-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/TailFile.java#L693
> {code}
> // Check if file has rotated
> if (rolloverOccurred
> || (timestamp <= file.lastModified() && length >
> file.length())
> || (timestamp < file.lastModified() && length >=
> file.length())) {
> // Since file has rotated, we close the reader, create a new one,
> and then reset our state.
> try {
> reader.close();
> getLogger().debug("Closed FileChannel {}", new
> Object[]{reader, reader});
> } catch (final IOException ioe) {
> getLogger().warn("Failed to close reader for {} due to {}",
> new Object[]{file, ioe});
> }
> reader = createReader(file, 0L);
> position = 0L;
> checksum.reset();
> }
> {code}
> The third condition, newer timestamp but the same file size can work
> negatively in some situations. For example:
> # If an already fully tailed file is 'touched' and last modified timestamp is
> updated. This is the easiest way to produce duplicated content.
> # On Windows, if a file is being tailed and updated by an app that writes
> logs or some data to it consistently and frequently, then the last modified
> timestamp can be delayed to be updated compared to file size. I couldn't find
> canonical docs for this behavior, but testing on Windows consistently
> produces duplicated data. And the 3rd condition becomes true when such
> duplication occurs.
> TailFile updates the file timestamp and length when it reads some data from
> the file, specifically at these lines:
> https://github.com/apache/nifi/blob/master/nifi-nar-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/TailFile.java#L765
> {code}
> timestamp = Math.max(state.getTimestamp(), file.lastModified());
> length = file.length();
> {code}
> As mentioned at the 2nd case above, file.lastModified can return a stale
> timestamp (or maybe just not being flushed yet) while length is replaced by
> the latest value. After this happens, at the next onTrigger cycle, the 3rd
> condition becomes true because it detects a newer timestamp.
> These conditions are added by NIFI-1170 and NIFI-1959.
> A simple flow, TailFile -> SplitText -> (FlowFiles are queued) ->
> UpdateAttribute(Stopped) can reproduce this, with a command-line to simulate
> frequently updated log file:
> {code}
> $ for i in `seq 1 10000`; do echo $i >> test.log; done
> {code}
> The expected result is having 10000 generated FlowFiles queued at the
> relationship between SplitText and UpdateAttribute. But on Windows, more
> FlowFiles are generated.
> By enabling debug level log for TailFile, following log messages can be
> confirmed:
> {code}
> Add this to conf/logback.xml
> <logger name="org.apache.nifi.processors.standard.TailFile" level="DEBUG"/>
> 2017-07-19 10:22:07,134 DEBUG [Timer-Driven Process Thread-3]
> o.a.nifi.processors.standard.TailFile TailFile[id=59ef6ea7-0
> 15d-1000-d6c2-c57a61e58a80] Recovering Rolled Off Files; total number of
> files rolled off = 0
> 2017-07-19 10:22:07,134 DEBUG [Timer-Driven Process Thread-3]
> o.a.nifi.processors.standard.TailFile
> TailFile[id=59ef6ea7-015d-1000-d6c2-c57a61e58a80] Closed FileChannel
> sun.nio.ch.FileChannelImpl@6d2a1eaf
> 2017-07-19 10:22:07,134 DEBUG [Timer-Driven Process Thread-3]
> o.a.nifi.processors.standard.TailFile
> TailFile[id=59ef6ea7-015d-1000-d6c2-c57a61e58a80] Created FileChannel
> sun.nio.ch.FileChannelImpl@4aefddb3 for C:\logs\test.log
> 2017-07-19 10:22:07,150 DEBUG [Timer-Driven Process Thread-3]
> o.a.nifi.processors.standard.TailFile
> TailFile[id=59ef6ea7-015d-1000-d6c2-c57a61e58a80] Reading lines starting at
> position 0
> {code}
> The 3rd condition should be removed to avoid having these duplicated data
> ingested. Or if there's any specific need, we should discuss about it and
> implement additional solution.
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