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From "Richard Hawkes (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (IO-279) Tailer erroneously considers file as new
Date Thu, 10 Jan 2013 11:42:13 GMT

    [ https://issues.apache.org/jira/browse/IO-279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13549558#comment-13549558
] 

Richard Hawkes commented on IO-279:
-----------------------------------

Guys, I have downloaded 2.4 which (I think) you are saying has fixed it. However, I notice
that the fileRotated is still getting called erroneously. I have done a fair bit of research
into this, and it would seem that the file.length() method is not always 100% up to date,
which leads to position occasionally being greater than file.length() !! Quite often it seems
to be a few miliseconds behind the actual position. I suppose with that much data bouncing
around the network.

I have added a check after the readLines(reader) to see if position is greater than file.length()
if it is, it waits a second. That seems to mop up this issue, although I know it's one ALMIGHTY
hack!
                
> 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
>            Reporter: Sergio Bossa
>             Fix For: 2.4
>
>         Attachments: IO-279.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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