I came across Sphinx today via the MySQL Performance Blog (which has some good entries you might want to check out). It is an Open Source Full Text SQL Search Engine. It can be installed as a storage engine type on MySQL, and from what I hear can beat the pants off of MySQL's built-in full text search in some cases.
From the web site:
Generally, it's a standalone search engine, meant to provide fast, size-efficient and relevant fulltext search functions to other applications. Sphinx was specially designed to integrate well with SQL databases and scripting …
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