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From "Marcelo Ochoa" <marcelo.oc...@gmail.com>
Subject Oracle and Lucene Integration
Date Wed, 22 Nov 2006 13:09:48 GMT
Hi all:
  I read on this a list many threads about Lucene indexing framework
integration with Oracle.
http://www.gossamer-threads.com/lists/lucene/java-user/41104?search_string=oracle%20jvm%20BLOB;#41104
  So it push me to work in a Lucene and Oracle JVM (a Java virtual
machine running inside the Oracle database).
  The reason to do this is:
   - Using traditional File System for storing the inverted index is
not a good option for some users.
   - Using BLOB for storing the inverted index running Lucene outside
the Oracle database has a bad performance because there are a lot of
network round trips and data marshalling.
   - Indexing relational data stores such as tables with VARCHAR2,
CLOB or XMLType with Lucene running outside the database has the same
problem as the previous point.
   - The JVM included inside the Oracle database can scale up to
10.000+ concurrent threads without memory leaks or deadlock and all
the operation on tables are in the same memory space!!
   With these points in mind, I uploaded the complete Lucene framework
inside the Oracle JVM and I runned the complete JUnit test case
successful, except for some test such as the RMI test which requires
special grants to open ports inside the database.
   The Lucene's test cases run faster inside the Oracle database (11g)
than the Sun JDK 1.5, because the classes are automatically JITed
after some executions.
   I had implemented and OJVMDirectory Lucene Store which replaces the
file system storage with a BLOB based storage, compared with a
RAMDirectory implementation is a bit slower but we gets all the
benefits of the BLOB storage (backup, concurrence control, and so on).
  The OJVMDirectory is cloned from the source at
http://issues.apache.org/jira/browse/LUCENE-150 (DBDirectory) but with
some changes to run faster inside the Oracle JVM.
  At this moment, I am working in a full integration with the SQL
Engine using the Data Cartridge API, it means using Lucene as a new
Oracle Domain Index.
  With this extension we can create a Lucene Inverted index in a table using:

create index it1 on t1(f2) indextype is LuceneIndex parameters('test');

  assuming that the table t1 has a column f2 of type VARCHAR2, CLOB or
XMLType, after this, the query against the Lucene inverted index can
be made using a new Oracle operator:

select * from t1 where contains(f2, 'Marcelo') = 1;

  the important point here is that this query is integrated with the
execution plan of the Oracle database, so in this simple example the
Oracle optimizer see that the column "f2" is indexed with the Lucene
Domain index, then using the Data Cartridge API a Java code running
inside the Oracle JVM is executed to open the search, a fetch all the
ROWID that match with "Marcelo" and get the rows using the pointer,
here the output:

SELECT STATEMENT	                              ALL_ROWS	3	1	115
        TABLE ACCESS(BY INDEX ROWID) LUCENE.T1		3	1	115
             DOMAIN INDEX LUCENE.IT1

  Another benefits of using the Data Cartridge API is that if the
table T1 has insert, update or delete rows operations a corresponding
Java method will be called to automatically update the Lucene Index.
  Well may be the email is so long, if anybody is interested in this
implementation I can put in a public web site.
   Best regards, Marcelo.

PD: For Oracle users the big question is, Why do I use Lucene instead
of Oracle Text which is implemented in C?
I think that the answer is too simple, Lucene is open source and
anybody can extend it and add the functionality needed :)
-- 
Marcelo F. Ochoa
http://marcelo.ochoa.googlepages.com/home
______________
Do you Know DBPrism? Look @ DB Prism's Web Site
http://www.dbprism.com.ar/index.html
More info?
Chapter 17 of the book "Programming the Oracle Database using Java &
Web Services"
http://www.amazon.com/gp/product/1555583296/
Chapter 21 of the book "Professional XML Databases" - Wrox Press
http://www.amazon.com/gp/product/1861003587/
Chapter 8 of the book "Oracle & Open Source" - O'Reilly
http://www.oreilly.com/catalog/oracleopen/

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