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https://issues.apache.org/jira/browse/IO-523?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16123104#comment-16123104
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Sebb commented on IO-523:
-------------------------
The behaviour needs to be optional to account for the case where the file has
been rewritten to the same size.
> 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: https://issues.apache.org/jira/browse/IO-523
> 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:
> {code:title=org.apache.commons.io.input.Tailer.java}
> // ----------- Lines 461 - 472 --------------
> // ...
> else if (newer) {
> /*
> * 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
> 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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