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https://issues.apache.org/jira/browse/LUCENE-5574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13959875#comment-13959875
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Shai Erera commented on LUCENE-5574:
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I think this is a good change -- it makes IndexReader more read-only in nature.
I.e. previously it could modify the index, then we made it read-only in that
aspect. Now we make it sort of read-only such that it cannot modify the
Directory. So I wonder, if we viewed IndexReader as a "user" with read-only
permissions on the index Directory, we wouldn't even attempt deleting unused
files by it, right? So maybe we should just do that -- never call IFD from an
nrt-reader.close() chain? Then, if you have a write open, it will eventually
delete those files, otherwise the files are there until you open a new writer?
As for MDW, what if on close() it attempted to open a writer w/ OpenMode.OPEN,
then close it, before it verifies there are no leftover files? Then the unused
files will get deleted, and we'd still have a check in MDW that we didn't leave
any writer/reader open, or leaking files?
> 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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