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From Thomas Becker <>
Subject Re: Performance tips when creating a large index from database.
Date Thu, 22 Oct 2009 14:50:50 GMT
Profile your application first hand and find out where the bottlenecks really
are during indexing.

For me it was clearly the database calls which took most of the time. Due to a
very complex SQL Query.
I applied the Producer - Consumer pattern and put a blocking queue in between. I
have a threadpool running x producers which are sending SQL Queries to the
database. Each returned row is put into the blockingQueue and another threadpool
running x (currently only 1) consumers is taking Objects from the row, converts
them to lucene documents and adds them to the index.
If the last row is put into the queue I add a Poison Pill to tell the consumer
to break.
Using a blockingQueue limited to 10.000 entries together with jdbc fetchSize
avoids high memory consumptions if too many producer threads return from the db.

This way I could reduce indexing time from around 8h to 30 min. (really). But be
careful. Load on the DB Server will surely increase.

Hope that helps.


Paul Taylor wrote:
> I'm building a lucene index from a database, creating 1 about 1 million
> documents, unsuprisingly this takes quite a long time.
> I do this by sending a query  to the db over a range of ids , (10,000)
> records
> Add these results in Lucene
> Then get next 10,0000 and so on.
> When completed indexing I then call optimize()
> I also set  indexWriter.setMaxBufferedDocs(1000) and 
> indexWriter.setMergeFactor(3000) but don't fully understand these values.
> Each document contains about 10 small fields
> I'm looking for some ways to improve performance.
> This index writing is single threaded, is there a way I can multi-thread
> writing to the indexing ?
> I only call optimize() once at the end, is the best way to do it.
> I'm going to run a profiler over the code, but are there any rules of
> thumbs on the best values to set for MaxBufferedDocs and Mergefactor()
> thanks Paul
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Thomas Becker
Senior JEE Developer

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