Apache Lucene

Apache Lucene is a high-performance, full-featured text search engine library written entirely in Java.

Lucene serves as the core indexing and search logic for industry giants like Elasticsearch and Solr. It provides powerful features including ranked searching, field-based sorting, and simultaneous update/search capabilities. By utilizing an inverted index structure, Lucene delivers sub-second query speeds across massive datasets (billions of documents). It is the gold standard for developers requiring granular control over tokenization, stemming, and scoring algorithms.

https://lucene.apache.org/