How does PostGreSQL compare?
I work at a large government department with stupidly large scientific datasets being thrown in and out of databases and we're migrating as fast as we can from Oracle to Postgres. The only thing we can't really shake is bloody Oracle financials and a few crufted old Java apps that we don't have the code to rewrite.
Postgres handles beautifully, and on some things even better although on some nasty multi-join type things Oracle will still beat it.
But it doesn't even matter because we can just throw more hardware at it infinitely cheaper than the extortion racket that Oracle pricing represents.
MariaDB is surprisingly competent too and in fact even has a surprisingly complete GIS implementation (Although PostGIS is the gold standard as far as we are concerned). Just avoid the Oracle branded one (MySQL), its not as well tuned, doesn't play nice with packaging systems and is generally posessed of the Oracle odour.