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From "Jack Krupansky" <>
Subject Re: Lucene Index backward compatibility related question
Date Mon, 27 Aug 2012 18:33:37 GMT
Technically, you should be able to use both 3.0 and 4.0 indexes in the same 
app, but a recent inquiry here indicated some unresolved problem. Here's the 
official statement from CHANGES.txt for 4.0-BETA:

" - On upgrading to 4.0, if you do not fully reindex your documents,
    Lucene will emulate the new flex API on top of the old index,
    incurring some performance cost (up to ~10% slowdown, typically).
    To prevent this slowdown, use oal.index.IndexUpgrader
    to upgrade your indexes to latest file format (LUCENE-3082).

    Mixed flex/pre-flex indexes are perfectly fine -- the two
    emulation layers (flex API on pre-flex index, and pre-flex API on
    flex index) will remap the access as required.  So on upgrading to
    4.0 you can start indexing new documents into an existing index.
    To get optimal performance, use oal.index.IndexUpgrader
    to upgrade your indexes to latest file format (LUCENE-3082)."

Bottom line: Write a test and see for yourself.

-- Jack Krupansky

-----Original Message----- 
From: Sitowitz, Paul
Sent: Wednesday, August 22, 2012 1:31 PM
Subject: Lucene Index backward compatibility related question


I have two products that are using Lucene: The first product creates the 
Lucene indexes for some data using Lucene version 3.01. The second product 
utilizes the indexes created by the first product for text search purposes 
and is also using Lucene 3.01.  I understand that the latest version of 
Lucene 4.0 has made several performance enhancements of which we would like 
to be able to leverage by our second product.

Question:   If we upgrade the second product to use Lucene 4.0, will we 
still be able to take advantage of search related performance gains while 
still using the index created using Lucene 3.01 by our first product? OR, 
will we have to "bite the bullet" and upgrade BOTH products to use the 
latest version of Lucene?

Thanks in advance for you response.


Paul Sitowitz

P a u l   S i t o w i t z
Core Engineering
VeriSign Naming Services

12061 Bluemont Way
Reston, VA 20190   (email)
703-948-3298                (office)
703-626-3593                (mobile)

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