In-memory DBMS vs. In-memory option
Read carefully. There are in-memory database management systems (SAP Hana, Oracle TimesTen, IBM solidDB, etc.) and then there are in-memory features being added to conventional databases (IBM BLU Acceleration for DB2, Microsoft In-Memory OLTP feature of Microsoft SQL Server 2014, the coming In-Memory Option for Oracle 12c). Everyone's promising "dramatic performance improvements" and "non disruption," but only SAP is also saying it can deliver "radical simplification." In my book (and from what customers tell me), non-disruption and radical simplification are mutually exclusive, so consider the business value before committing everything to an in-memory approach.