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From "Casey Doerschuk (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (IO-279) Tailer erroneously considers file as new
Date Fri, 26 Jul 2013 17:47:49 GMT

    [ https://issues.apache.org/jira/browse/IO-279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13720991#comment-13720991
] 

Casey Doerschuk commented on IO-279:
------------------------------------

Just wanted to confirm to anyone who cares, commons-io 2.4 tag with the April patch attached
to this JIRA, still has the issue in the scenerio we are using it. We have a daemon network
listener process written in C++ that opens a log file, appends new data, closes the file,
repeatedly, for which we are trying to use the Tailer classes to pump the log through Kafka,
similar to Herman in the above thread. Using commons-io 2.4 prebuilt jar we were getting the
intermittent reatart on almost all hosts more than once a day. Using the patched jar it happened
less, but still happens. I am trying the forked version in github published by Sergio. I will
respond with my findings.
                
> Tailer erroneously considers file as new
> ----------------------------------------
>
>                 Key: IO-279
>                 URL: https://issues.apache.org/jira/browse/IO-279
>             Project: Commons IO
>          Issue Type: Bug
>    Affects Versions: 2.0.1, 2.4
>            Reporter: Sergio Bossa
>         Attachments: fix-tailer.patch, IO-279.patch, modify-test-fixed.patch, modify-test.patch
>
>
> Tailer sometimes erroneously considers the tailed file as new, forcing a repositioning
at the start of the file: I'm still unable to reproduce this in a test case, because it only
happens to me with huge log files during Apache Tomcat startup.
> This is the piece of code causing the problem:
> {code}
> // See if the file needs to be read again
> if (length > position) {
>     // The file has more content than it did last time
>     last = System.currentTimeMillis();
>     position = readLines(reader);
> } else if (FileUtils.isFileNewer(file, last)) {
>     /* This can happen if the file is truncated or overwritten
>         * with the exact same length of information. In cases like
>         * this, the file position needs to be reset
>         */
>     position = 0;
>     reader.seek(position); // cannot be null here
>     // Now we can read new lines
>     last = System.currentTimeMillis();
>     position = readLines(reader);
> }
> {code}
> What probably happens is that the new file content is about to be written on disk, the
date is already updated but content is still not flushed, so actual length is untouched and
there you go.
> In other words, I think there should be some better method to verify the condition above,
rather than relying only on dates: keeping and comparing the hash code of the latest line
may be a solution, but may hurt performances ... other ideas?

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