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https://issues.apache.org/jira/browse/LUCENE-1705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12722172#action_12722172
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Michael McCandless commented on LUCENE-1705:
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This should be simple to implement, by taking the logic that's now in
IndexWriter's init method (under the {{if (create) {}}) and pulling out into a
separate method.
>From IndexWriter's standpoint, this is just another commit, on equal footing
>with all prior commits even though it up and deleted all segments. So eg a
>deletion policy could choose to keep those past commits around, IndexReaders
>can open those past commits, etc.
One good functional gain by offering this method is it could be done within a
single IndexWriter transaction. Ie you could deleteAll, make further changes,
etc., but then change your mind and rollback the entire transaction. Whereas,
requiring if you close & re-open the writer with create=true, you've
necessarily committed the change to the index.
So I don't think we should implicitly do a commit() from within deleteAll(); I
think the user should call commit() on their own.
> Add deleteAllDocuments() method to IndexWriter
> ----------------------------------------------
>
> Key: LUCENE-1705
> URL: https://issues.apache.org/jira/browse/LUCENE-1705
> Project: Lucene - Java
> Issue Type: Wish
> Components: Index
> Affects Versions: 2.4
> Reporter: Tim Smith
>
> Ideally, there would be a deleteAllDocuments() or clear() method on the
> IndexWriter
> This method should have the same performance and characteristics as:
> * currentWriter.close()
> * currentWriter = new IndexWriter(..., create=true,...)
> This would greatly optimize a delete all documents case. Using
> deleteDocuments(new MatchAllDocsQuery()) could be expensive given a large
> existing index.
> IndexWriter.deleteAllDocuments() should have the same semantics as a
> commit(), as far as index visibility goes (new IndexReader opening would get
> the empty index)
> I see this was previously asked for in LUCENE-932, however it would be nice
> to finally see this added such that the IndexWriter would not need to be
> closed to perform the "clear" as this seems to be the general recommendation
> for working with an IndexWriter now
> deleteAllDocuments() method should:
> * abort any background merges (they are pointless once a deleteAll has been
> received)
> * write new segments file referencing no segments
> This method would remove one of the final reasons i would ever need to close
> an IndexWriter and reopen a new one
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