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https://issues.apache.org/jira/browse/LUCENE-5574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13959900#comment-13959900
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Shai Erera commented on LUCENE-5574:
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I looked at MDW.close() and looks like it already does that -- it opens IW and
close it, then diff the files before and after the close -- so that idea is not
new :). That way it protects against e.g. IFD bugs (or bugs elsewhere where you
don't decRef() a file or something).
But perhaps we can make MDW lenient by default
(assertNoUnreferencedFilesOnClose=false) and turn it on in tests where we'd
like to catch IFD bugs? Then in the majority of tests we can code "normally",
but in the few tests that need to make sure IW is bullet-proof, we make sure to
close things in order?
Another idea I had is to use the newly added checksums to make sure that the
file we're about to delete has the checksum that we think it should have. Of
course, if you re-index the exact same set of documents in the exact same
order, this is still a false positive, but I don't know how common that is. But
then, I'm not sure if it's ok to rely on such logic, and perhaps the simplest
thing we could do is treat the Directory read-only by IndexReader instances.
> NRT Reader close can wipe index it doesn't own
> ----------------------------------------------
>
> Key: LUCENE-5574
> URL: https://issues.apache.org/jira/browse/LUCENE-5574
> Project: Lucene - Core
> Issue Type: Bug
> Components: core/index
> Affects Versions: 4.8, 5.0, 4.7.1
> Reporter: Simon Willnauer
> Priority: Critical
> Fix For: 4.8, 5.0
>
> Attachments: LUCENE-5574.patch, LUCENE-5574.patch, LUCENE-5574.patch
>
>
> Today NRT Readers try to clean up unused files via their IW reference when
> they are closed. Yet, if the index writer is already closed another index
> could have been created on the same directory which can create the same files
> as the IW before. For the NRT Reader those files are not referenced and it
> will simply wipe them away. If you use this in a replication scenario where
> directories are reused this can simply wipe your index away or in combination
> with the FSync issue LUCENE-5570 create 0-byte files. I have a test that
> reproduces this issue
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