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From "Chris Lu" <chris...@gmail.com>
Subject sharing my experience for upgrading from Lucene 1.9 to Lucene 2.2-dev
Date Thu, 08 Mar 2007 02:32:22 GMT
I would like to share my experience for upgrading from Lucene 1.9 to
Lucene 2.2, build 515893.

I have been working on a product called DBSight. It has both a
designing web UI for configuring database crawl, and also capabilities
to serve search requests like later-emerged SOLR. So DBSight can do
both indexing and searching. Previously I have upgraded to 1.3, 1.4,
and 1.9, all were pretty easy and went through well. Upgrading to 2.2
isn't so straight forward though.

Last time when Lucene 2.0 came out, I tried it by simply dropping
lucene-2.0.jar onto the classpath. The indexing went well, but somehow
the searching didn't work any more, no results and without any
exceptions! That's wierd and I have to back off.

Now with Lucene 2.2, I tried it again. This time, there are a bunch of
NullPointerException when starting DBSight. But at least I can fix
those. So I take some time to write down anything that may need to
change. Your code may differ depending on which API you use.

1. Use document.getFields() instead of deprecated document.fields()
  This is an easy one, but with some code change. The return type
changed from Enumeration to List. So you may need to write 2~3 lines
of code. The upgrading should be easy and not even need a QA(really?).
2. Use FSDirectory.getDirectory(file) instead of
FSDirectory.getDirectory(file, isCreating)
  FSDirectory.getDirectory(file) will not automatically create
directory any more. I missed this deprecated yet convenient parameter.
However, not so bad.
3. RAMDirectory related changes
  It took me something to find this out. Previously, after
    ramDirectory = new RAMDirectory(file)
  I could ramDirectory.close() to release the resources. And later, I
could do a check for IndexReader.indexExists(ramDirectory) to see if
there is an index in the directory. FSDirectory behaves this way also.
  But with lucene 2.2, NullPointerExceptions came out. It turns out
when ramDirectory.close(), the instance variable fileMap is set to
null. And IndexReader.indexExists(ramDirectory) is reading fileMap to
look for indexes, causing the NPE.
4. clearing remaining locks from last indexing
  In order to clear indexing locks, previously I manually cleared
write lock and commit lock. As pointed out by others, the commit lock
now is gone. And the unlocking logic is already wrapped in
IndexReader.unlock(directory), I should use that directly.

In general, the upgrade is smooth, and I can compile Lucene in JDK 1.4
without any problem.

Now I can try out the new optimizations and features, especially on
merging, and test out whether the query performance improves or not.
This feature sounds interesting:
indexWriter.addIndexesNoOptimize(directories), but the result is, no
obvious speedup, and the worst part: the dreaded "java.io.IOException:
read past EOF". Guess I will skip this feature for now.

-- 
Chris Lu
-------------------------
Instant Full-Text Search On Any Database/Application
site: http://www.dbsight.net
demo: http://search.dbsight.com

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