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https://issues.apache.org/jira/browse/LUCENE-773?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12464586
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Nicolas Lalevée commented on LUCENE-773:
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I was working on the IndexFormat mechanism, LUCENE-622 being the first draft of
it. And I have tried to use some Java-1.5 parametered types to see if it is
possible to make index readers/writers typed by the index format. And I am in
front of one issue : the directory have to know the index format because of the
IndexNameFilter and the create feature. And I don't think it is a good idea
because of how they are instanciated.
I have not finished the design of this Java-1.5-way-of-typing, I have other
issues to look at, but I vote +1 for removing any index structure specificity
in the store package.
> Deprecate "create" method in FSDirectory.getDirectory in favor of
> IndexWriter's "create"
> ----------------------------------------------------------------------------------------
>
> Key: LUCENE-773
> URL: https://issues.apache.org/jira/browse/LUCENE-773
> Project: Lucene - Java
> Issue Type: Improvement
> Affects Versions: 1.9, 2.0.0, 2.0.1, 2.1
> Reporter: Michael McCandless
> Assigned To: Michael McCandless
> Priority: Minor
>
> It's confusing that there is a create=true|false at the FSDirectory
> level and then also another create=true|false at the IndexWriter
> level. Which one should you use when creating an index?
> Our users have been confused by this in the past:
> http://www.gossamer-threads.com/lists/lucene/java-user/4792
> I think in general we should try to have one obvious way to achieve
> something (like Python: http://en.wikipedia.org/wiki/Python_philosophy).
> And the fact that there are now two code paths that are supposed to do
> the same (similar?) thing, can more easily lead to sneaky bugs. One
> case of LUCENE-140 (already fixed in trunk but not past releases),
> which inspired this issue, can happen if you send create=false to the
> FSDirectory and create=true to the IndexWriter.
> Finally, as of lockless commits, it is now possible to open an
> existing index for "create" while readers are still using the old
> "point in time" index, on Windows. (At least one user had tried this
> previously and failed). To do this, we use the IndexFileDeleter class
> (which retries on failure) and we also look at the segments file to
> determine the next segments_N file to write to.
> With future issues like LUCENE-710 even more "smarts" may be required
> to know what it takes to "create" a new index into an existing
> directory. Given that we have have quite a few Directory
> implemenations, I think these "smarts" logically should live in
> IndexWriter (not replicated in each Directory implementation), and we
> should leave the Directory as an interface that knows how to make
> changes to some backing store but does not itself try to make any
> changes.
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