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From "Raghavendra Prabhu" <>
Subject Re: Lucene indexing on Hadoop distributed file system
Date Sun, 26 Mar 2006 08:03:39 GMT
I would like to see lucene operate with hadoop

As you rightly pointed out, writing using FSDirectory to DFS would be a
performance issue.

I am interested in the idea. But i do not know how much time i can
contribute to this because of the little time which i can spare.

If anyone else is interested, can they join ? We can work on this together


On 3/26/06, Igor Bolotin <> wrote:
> In my current project we needed a way to create very large Lucene indexes
> on
> Hadoop distributed file system. When we tried to do it directly on DFS
> using
> Nutch FsDirectory class - we immediately found that indexing fails because
> method throws UnsupportedOperationException. The
> reason for this behavior is clear - DFS does not support random updates
> and
> so seek() method can't be supported (at least not easily).
> Well, if we can't support random updates - the question is: do we really
> need them? Search in the Lucene code revealed 2 places which call
> method: one is in TermInfosWriter and another one in
> CompoundFileWriter. As we weren't planning to use CompoundFileWriter - the
> only place that concerned us was in TermInfosWriter.
> TermInfosWriter uses in its close() method to write
> total
> number of terms in the file back into the beginning of the file. It was
> very
> simple to change file format a little bit and write number of terms into
> last 8 bytes of the file instead of writing them into beginning of file.
> The
> only other place that should be fixed in order for this to work is in
> SegmentTermEnum constructor - to read this piece of information at
> position
> = file length - 8.
> With this format hack - we were able to use FsDirectory to write index
> directly to DFS without any problems. Well - we still don't index directly
> to DFS for performance reasons, but at least we can build small local
> indexes and merge them into the main index on DFS without copying big main
> index back and forth.
> If somebody is interested - I can post our changes in TermInfosWriter and
> SegmentTermEnum code, although they are pretty trivial.
> Best regards!
> Igor

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