Sphinx is a full-text search engine, publicly distributed under GPL version 2. Commercial licensing (eg. for embedded use) is available upon request.
Technically, Sphinx is a standalone software package provides fast and relevant full-text search functionality to client applications. It was specially designed to integrate well with SQL databases storing the data, and to be easily accessed scripting languages. However, Sphinx does not depend on nor require any specific database to function.
Applications can access Sphinx search daemon (searchd) using any of the three different access methods: a) via native search API (SphinxAPI), b) via Sphinx own implementation of MySQL network protocol (using a small SQL subset called SphinxQL), or c) via MySQL server with a pluggable storage engine (SphinxSE).
Official native SphinxAPI implementations for PHP, Perl, Ruby, and Java are included within the distribution package. API is very lightweight so porting it to a new language is known to take a few hours or days. Third party API ports and plugins exist for Perl, C#, Haskell, Ruby-on-Rails, and possibly other languages and frameworks.
Starting version 1.10-beta, Sphinx supports two different indexing backends: “disk” index backend, and “realtime” (RT) index backend. Disk indexes support online full-text index rebuilds, but online updates can only be done on non-text (attribute) data. RT indexes additionally allow for online full-text index updates. Previous versions only supported disk indexes.
Data can be loaded into disk indexes using a so-called data source. Built-in sources can fetch data directly from MySQL, PostgreSQL, ODBC compliant database (MS SQL, Oracle, etc), or a pipe in a custom XML format. Adding new data sources drivers (eg. to natively support other DBMSes) is designed to be as easy as possible. RT indexes, as of 1.10-beta, can only be populated using SphinxQL.
As for the name, Sphinx is an acronym which is officially decoded as SQL Phrase Index. Yes, I know about CMU's Sphinx project.
1.2. Sphinx features
Key Sphinx features are:
high indexing and searching performance;
advanced indexing and querying tools (flexible and feature-rich text tokenizer, querying language, several different ranking modes, etc);
advanced result set post-processing (SELECT with expressions, WHERE, ORDER BY, GROUP BY etc over text search results);
proven scalability up to billions of documents, terabytes of data, and thousands of queries per second;
easy integration with SQL and XML data sources, and SphinxAPI, SphinxQL, or SphinxSE search interfaces;
easy scaling with distributed searches.
To expand a bit, Sphinx:
has high indexing speed (upto 10-15 MB/sec per core on an internal benchmark);
has high search speed (upto 150-250 queries/sec per core against 1,000,000 documents, 1.2 GB of data on an internal benchmark);
has high scalability (biggest known cluster indexes over 3,000,000,000 documents, and busiest one peaks over 50,000,000 queries/day);
provides good relevance ranking through combination of phrase proximity ranking and statistical (BM25) ranking;
provides distributed searching capabilities;
provides document excerpts (snippets) generation;
provides searching from within application with SphinxAPI or SphinxQL interfaces, and from within MySQL with pluggable SphinxSE storage engine;
supports boolean, phrase, word proximity and other types of queries;
supports multiple full-text fields per document (upto 32 by default);
supports multiple additional attributes per document (ie. groups, timestamps, etc);
supports morphological word forms dictionaries;
supports tokenizing exceptions;
supports both single-byte encodings and UTF-8;
supports stemming (stemmers for English, Russian and Czech are built-in; and stemmers for French, Spanish, Portuguese, Italian, Romanian, German, Dutch, Swedish, Norwegian, Danish, Finnish, Hungarian, are available by building third party libstemmer library);
supports MySQL natively (all types of tables, including MyISAM, InnoDB, NDB, Archive, etc are supported);
supports PostgreSQL natively;
supports ODBC compliant databases (MS SQL, Oracle, etc) natively;
…has 50+ other features not listed here, refer to API and configuration manual!
1.3. Where to get Sphinx
Sphinx is available through its official Web site at http://sphinxsearch.com/.
Currently, Sphinx distribution tarball includes the following software:
indexer: an utility which creates fulltext indexes;
search: a simple command-line (CLI) test utility which searches through fulltext indexes;
searchd: a daemon which enables external software (eg. Web applications) to search through fulltext indexes;
sphinxapi: a set of searchd client API libraries for popular Web scripting languages (PHP, Python, Perl, Ruby).
spelldump: a simple command-line tool to extract the items from an ispell or MySpell (as bundled with OpenOffice) format dictionary to help customize your index, for use with wordforms.
indextool: an utility to dump miscellaneous debug information about the index, added in version 0.9.9-rc2.