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https://issues.apache.org/jira/browse/LUCENE-4190?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13409739#comment-13409739
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Michael McCandless commented on LUCENE-4190:
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bq. I think that the way to "bound" the namespace of files is to put everything
in a subdirectory of the index directory chosen by the user and control the
name of that subdirectory, making it clear that this is semi-private to Lucene
and that all files in that subdirectory are fair game.
I think this idea is compelling. It would clearly succeed in creating
a private namespace (unless someone had happened to separately create
a directory named 'lucene.index' there, which seems very unlikely).
For back compat... if we open an existing index (not in the subdir),
we'd have to just continue writing there? But when creating a new
index, we'd create the subdir and write files into it (and maybe we
fix index upgrader to somehow move the files to the subdir?).
We could make this change for 4.0 Beta, but it wouldn't be until 6.0
that we could remove the back compat (which is fine).
Hmm but then an old index would never actually migrate "forward". Not
quite sure how to do the transition ...
It seems like a rather big change, which makes me nervous ... and I
imagine apps will be confused eg when they try to replicate or backup
(but, they'd just have to fix themselves: apps can't rely on the index
files).
It seems less risky to start with the current patch; in fact I think
the two changes can be done separately?
> 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, 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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