Sphinx: Open Source SQL Full Text Search Engine

Sphinx is a full-text search engine. It is a standalone search engine, meant to provide fast, size-efficient and relevant full-text search functions to other applications. Sphinx was specially designed to integrate well with SQL databases and scripting languages.
Currently built-in data source drivers support fetching data either via direct connection to MySQL, or PostgreSQL, or from a pipe in a custom XML format. Adding new drivers (eg. to natively support some other DBMSes) is designed to be as easy as possible.
Search API is natively ported to PHP, Python, Perl, Ruby, Java, and also available as a pluggable MySQL storage engine. API is very lightweight so porting it to new language is known to take a few hours.
It features

• high indexing speed (upto 10 MB/sec on modern CPUs)
• high search speed (avg query is under 0.1 sec on 2-4 GB text collections)
• high scalability (upto 100 GB of text, upto 100 M documents on a single CPU)
• supports distributed searching (since v.0.9.6)
• supports MySQL natively (MyISAM and InnoDB tables are both supported)
• supports phrase searching
• supports phrase proximity ranking, providing good relevance
• supports English and Russian stemming
• supports any number of document fields (weights can be changed on the fly)
• supports document groups
• supports stopwords
• supports different search modes (”match all”, “match phrase” and “match any” as of v.0.9.5)
• generic XML interface which greatly simplifies custom integration
• pure-PHP (ie. NO module compiling etc) search client API

Currently known systems Sphinx has been successfully running on are:

• Linux 2.4.x, 2.6.x (various distributions)
• Windows 2000, XP
• FreeBSD 4.x, 5.x, 6.x
• NetBSD 1.6, 3.0
• Solaris 9, 11
• Mac OS X