Lucene is used at Yelp to power various search services including business search, phone search, and review search. The index is split across multiple machines ("federation") to address performance issues from disk seek latency and the large index size. Lucy is used for indexing and searching across the federated index. The federator combines results from shards. Techniques like successive geobounds relaxation and efficiently retrieving the top k hits based on binomial distribution are used to improve search performance.