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https://issues.apache.org/jira/browse/LUCENE-4190?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13406874#comment-13406874
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Shai Erera commented on LUCENE-4190:
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What if we had an object called IndexFileNames with a method accept(String
name), that returns true if the file is recognized, false otherwise - that
could give applications a way to create a recognized-set of index files:
* Lucene would provide a DefaultIndexFileNames which recognizes all non-codec
files
* Either the app would provide an extension to the default (or a wrapper) which
recognizes its codec files as well
** Or, we make the Codec responsible for recognizing files too, and then the
code would just query the Codec for non-default index files.
Either way, it seems like we can very easily recognize what are index files and
what aren't.
When files need to be deleted, it seems simple as well:
* Lucene lists all files in the directory
* Any file that is referenced by the index (I assume we still know which files
are needed right?) is kept
* Any other file is queried against IndexFileNames.accept and if it is
accepted, it's deleted, otherwise it's left alone.
Since this looks too simple to me, I'm assuming that I'm missing something. If
so, can someone please clarify the problem to me?
> IndexWriter deletes non-Lucene files
> ------------------------------------
>
> Key: LUCENE-4190
> URL: https://issues.apache.org/jira/browse/LUCENE-4190
> Project: Lucene - Java
> Issue Type: Bug
> Reporter: Michael McCandless
> Assignee: Robert Muir
> Fix For: 4.0, 5.0
>
> Attachments: LUCENE-4190.patch, LUCENE-4190.patch
>
>
> Carl Austin raised a good issue in a comment on my Lucene 4.0.0 alpha blog
> post:
> http://blog.mikemccandless.com/2012/07/lucene-400-alpha-at-long-last.html
> IndexWriter will now (as of 4.0) delete all foreign files from the index
> directory. We made this change because Codecs are free to write to any files
> now, so the space of filenames is hard to "bound".
> But if the user accidentally uses the wrong directory (eg c:/) then we will
> in fact delete important stuff.
> I think we can at least use some simple criteria (must start with _, maybe
> must fit certain pattern eg _<base36>(_X).Y), so we are much less likely to
> delete a non-Lucene file....
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