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From Michael McCandless <luc...@mikemccandless.com>
Subject Re: Near Real Time for multiple applications
Date Tue, 06 Nov 2012 12:31:37 GMT
On Mon, Nov 5, 2012 at 6:33 PM, Scott Smith <ssmith@mainstreamdata.com> wrote:
> I've been reading about NRT thinking it might be good to integrate it into my code. 
However, I have a question.
>
> Suppose that the index writer and the index reader run in totally different JVMs (i.e.,
they are different applications and only communicate via the disk).  Am I correct in thinking
that NRT isn't going to do anything for me?

That's correct: NRT is only usable if IndexReader/IndexWriter are in
the same JVM.

This is because we carry the deleted documents (bit vectors) in
memory, passing them from writer to reader on reopen.  We also don't
write a new segments_N file.

This is actually a limitation in Lucene's implementation: it would in
theory be possible to write the deleted docs, write a segments file
(but not fsync them, since it's not a commit), and then another JVM
process with access to that same filesystem could do an ordinary
reopen.  It'd be slower than NRT is now, since deleted docs are going
through the filesystem, and the reader would have to list the
directory to see the new segments file, but would still be (typically)
much faster than a commit...

Mike

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