The data to be indexed can generally come from very different sources: SQL databases, plain text files, HTML files, mailboxes, and so on.

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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. Data can be loaded into disk indexes using a so-called data source.

Official native Sphinx API implementations for PHP, Perl, Python, 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.

Actually, each and every important aspect was a problem: Despite the amount of time passed and numerous improvements made in the other solutions, there's still no solution which I personally would be eager to migrate to.

Considering that and a lot of positive feedback received from Sphinx users during last years, the obvious decision is to continue developing Sphinx (and, eventually, to take over the world).

None of the different querying methods are deprecated, but as of version 2.2.1-beta, Sphinx QL is the most advanced method.

We plan to remove Sphinx API and Sphinx SE someday so it would be a good idea to start using Sphinx QL.

Built-in sources can fetch data directly from My SQL, Postgre SQL, MSSQL, ODBC compliant database (Oracle, etc) or a pipe in TSV or a custom XML format. 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 Sphinx QL.

Sphinx is a full-text search engine, publicly distributed under GPL version 2. It was specially designed to integrate well with SQL databases storing the data, and to be easily accessed by scripting languages.