Merging several taxonomy indexes for faceted search

Question

I am planing to change my existing lucene index to use the new facets introduced in lucene 3.4.0.

Unfortunately, documentation is still a bit sparse, so I could not find an answer to my question:

I create a relatively large index of 8 million books by dividing it into several smaller groups of documents, creating indices for them, and then joining them all together to one big index using IndexWriter.addIndexes.

This allows the work to be split among several threads or even computers.

I now would like to add faceted search capabilities to my index, but I have the following problem: How can I merge/add/join several taxonomy indexes as created by LuceneTaxonmyWriter?

Answer 1

I asked the same question on the lucene mailing list and they pointed me to the class TaxonomyMergeUtils that is part of the examples for the lucene-facets module.

This class contains the code needed to merge two indexes together with their taxonomy index.

Note: If you are using the maven package, the examples are not included, you will have to download the complete lucene package (and probably its source code as well) from the website.