“Searching via SphinxAPI is as simple as 3 lines of code, and querying via SphinxQL is even simpler, with search queries expressed in good old SQL.”
Open source with commercial support
Result relevance ranking is the default. You can set up your own sorting should you wish, and give specific fields higher weightings.
The search service daemon (searchd) is pretty low on memory usage – and you can set limits on how much memory the indexer process uses too.
API for:
Java, PHP, Python, Ruby, Perl, C, and other languages.
Written in C++
Stats
60+ MB/sec per server
500+ queries/sec
Biggest known Sphinx cluster indexes 5 billion documents, resulting in over 6 TB of data. Busiest known one is, unsurpisingly, Craigslist, that serves 50+ million search queries/day.