Pretty much everyone here knows Lucene as the primary text-search engine these days, but there's a competitor Sphinx Search which is written in C or C++ and is

Pretty much everyone here knows Lucene as the primary text-search engine these days, but there's a competitor Sphinx Search which is written in C or C++ and is much lighter, to the point of being feasible as bundled with desktop software. It however has a bit weird database structure since text indexing is the primary use-case―this is being corrected in the third version with support for secondary indexes, but v3 isn't open-source yet. Not to be confused with Sphinx the documentation builder.