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https://issues.apache.org/jira/browse/LUCENE-6171?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15327898#comment-15327898
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Michael McCandless commented on LUCENE-6171:
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bq. does each update create a new one, perhaps in parallel-index like manner?
That's what we do ... we always fully write the new doc values to another file,
and stop referencing the old one.
> Make lucene completely write-once
> ---------------------------------
>
> Key: LUCENE-6171
> URL: https://issues.apache.org/jira/browse/LUCENE-6171
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Robert Muir
> Assignee: Michael McCandless
> Attachments: LUCENE-6171.patch
>
>
> Today, lucene is mostly write-once, but not always, and these are just very
> exceptional cases.
> This is an invitation for exceptional bugs: (and we have occasional test
> failures when doing "no-wait close" because of this).
> I would prefer it if we didn't try to delete files before we open them for
> write, and if we opened them with the CREATE_NEW option by default to throw
> an exception, if the file already exists.
> The trickier parts of the change are going to be IndexFileDeleter and
> exceptions on merge / CFS construction logic.
> Overall for IndexFileDeleter I think the least invasive option might be to
> only delete files older than the current commit point? This will ensure that
> inflateGens() always avoids trying to overwrite any files that were from an
> aborted segment.
> For CFS construction/exceptions on merge, we really need to remove the custom
> "sniping" of index files there and let only IndexFileDeleter delete files. My
> previous failed approach involved always consistently using
> TrackingDirectoryWrapper, but it failed, and only in backwards compatibility
> tests, because of LUCENE-6146 (but i could never figure that out). I am
> hoping this time I will be successful :)
> Longer term we should think about more simplifications, progress has been
> made on LUCENE-5987, but I think overall we still try to be a superhero for
> exceptions on merge?
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