Lucene - comparing data in multiple indexes

Question

Is it possible to compare data from multiple Lucene indexes? I would like to get documents that have the same value in similar fields (like first name, last name) across two indexes. Does Lucence support queries that can do this?

Answer 1

Well, partly. You can build identical document schemas across indexes, and at least get the set of hits correctly. However, as the Lucene Similarity documentation shows, the idf (inverse document frequency) factor in the Lucene scoring depends both on the index size and the number of documents having the search term in the index. Both these factors are index-dependent. Therefore the same match from different indexes may get different scores depending on these factors.