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From "Tyler Murry (JIRA)" <>
Subject [jira] [Updated] (IO-523) Do not reload the entire file when a tailed file's length and position are the same but the file is newer
Date Sun, 27 Nov 2016 05:34:59 GMT


Tyler Murry updated IO-523:
    Attachment: IO-523.patch

This is the patch file to remove the entire branch of code in the run() method. 

I could find a unit test that logically covered this block of code. The testTrailer method
in TrailerTest technically covers those lines, but it was not truly validating the logic of
the branch.

Since the branch is being removed, there are no changes to the unit test.

> Do not reload the entire file when a tailed file's length and position are the same but
the file is newer
> ---------------------------------------------------------------------------------------------------------
>                 Key: IO-523
>                 URL:
>             Project: Commons IO
>          Issue Type: Improvement
>          Components: Streams/Writers
>    Affects Versions: 2.5
>         Environment: Windows 10
>            Reporter: Tyler Murry
>            Priority: Minor
>         Attachments: IO-523.patch
>   Original Estimate: 24h
>  Remaining Estimate: 24h
> In the Tailer class, when the file length is equal to the position and the file is newer,
the following branch is executed:
> {}
> // ----------- Lines 461 - 472 --------------
> // ...
> else if (newer) {
>   /*
>    * This can happen if the file is truncated or overwritten with the exact same length
>    * information. In cases like this, the file position needs to be reset
>    */
>   position = 0;
>; // cannot be null here
>   // Now we can read new lines
>   position = readLines(reader);
>   last = file.lastModified();
> }
> // ...
> {code}
> The comments in the branch specifically mention wanting to reset the position and reload
the entire file. However, I believe this can lead to undesirable effects in certain cases.
> One example is when you are tailing one file into another file. If this branch is hit,
the entire input file is recopied into the output file. This is especially troublesome if
you have a rouge file who's timestamp changes regularly without any content changes.
> My improvement would be to simply remove this branch if it works for the general case
as well. Or, at least for special cases, allow a parameter to be checked to prevent this behavior.

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