The Oracle Database In-Memory option is a new memory-optimized database technology that implements an in-memory columnar data format to deliver extremely fast SQL processing.
The Oracle Database In-Memory option requires an In-Memory column store, which is a new component of the SGA called the In-Memory Area.
You can allocate as little or as much memory as you wish to the In-Memory Area. The larger the In-Memory Area, the greater the number of objects that can be populated into the In-Memory column store.
To check you’re in-memory results against disk queries parameter is
This can be enabled in two ways
0 - default no check
2 - basic lightweight
4 - heavyweight (Oracle Regression testing uses 4).