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From Apache Wiki <wikidi...@apache.org>
Subject [Nutch Wiki] Update of "bin/nutch solrdedup" by LewisJohnMcgibbney
Date Sun, 03 Jul 2011 03:40:53 GMT
Dear Wiki user,

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The "bin/nutch solrdedup" page has been changed by LewisJohnMcgibbney:
http://wiki.apache.org/nutch/bin/nutch%20solrdedup

Comment:
Update to reflect Nutch 1.3 API

New page:
Solrdedup is an alias for org.apache.nutch.indexer.solr.SolrDeleteDuplicates

As the name suggests this is a utility class for deleting duplicate documents from within
a solr index. 

The algorithm goes like follows:

'''Preparation''':
Query the solr server for the number of documents (say, N), Partition N among M map tasks.
For example, if we have two map tasks the first map task will deal with solr documents from
0 - (N / 2 - 1) and the second will deal with documents from (N / 2) to (N - 1). This can
be thought of as a linearly executing divide and conquer algorithm.

'''MapReduce''':
 * Map: Identity map where keys are digests and values are {@link SolrRecord} instances(which
contain id, boost and timestamp)

 * Reduce: After map, {@link SolrRecord}s with the same digest will be grouped together. Now,
of these documents with the same digests, delete all of them except the one with the highest
score (boost field). If two (or more) documents have the same score, then the document with
the latest timestamp is kept. Again, every other is deleted from solr index.

Note that unlike {@link DeleteDuplicates} we assume that two documents in a solr index will
never have the same URL. So this class only deals with documents with '''different''' URLs
but the same digest.

Usage:
{{{
bin/nutch solrdedup <solr url>
}}}

'''<solr url>''': Luckily all of the hard work is encapsulated within the class therefore
the onyl parameter we pass is our SolrURL e.g. ''http://localhost:8983/solr/''


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