I haven't ever worked at a giganto company myself - even though I've worked with largeish amounts of data... from multi-teribyte pyradmically stored JPEG2000s to 50GB tables of raw rows parsed from ridiculously long documents. I suspect some big places are indeed using Oracle - but notably large companies are still using MySQL or Postgres to great effect (i.e. Facebook).
Oracle was massive in the private sector 10 years ago, and it probably still is once you dig past the surface layer of nosql
Don’t forget that for a long term it was either Oracle or DB2