Did an exhaustive research for some payment processing system where we examined rdbms, document and other DB types. We could find no niche or feature set that

Did an exhaustive research for some payment processing system where we examined rdbms, document and other DB types. We could find no niche or feature set that wasn't better satisfied by either SQL server, Postresql, or Oracle RAC (in the rdbms area). Depending what you needed to optimize for (cost, clustering, ease of use, performance, tooling).