For full text search, the only global frequency information Postgres uses is the stop-word list. It does not do TF-IDF ranking. [1] For example, if you search

For full text search, the only global frequency information Postgres uses is the stop-word list. It does not do TF-IDF ranking. [1] For example, if you search for "Bob Peterson", Postgres will rank these two documents the same: "I saw Bob." "I saw Peterson." In contrast, an IDF-aware search would notice that "Peterson" occurs in fewer documents than "Bob" and score "I saw Peterson" higher for that reason. [1] http://en.wikipedia.org/wiki/Tf%E2%80%93idf http://en.wikipedia.org/wiki/Tf%E2%80%93idf [2] http://stackoverflow.com/questions/18296444/does-postgresql-use-tf-idf http://stackoverflow.com/questions/18296444/does-postgresql-...