The TimesTen In-Memory Database is optimized for low latency OLTP workloads.
A disk based database such as Oracle stores all of its data on disk and a subset of its data in the SGA. Oracle uses a buffer pool/cache to transfer data blocks to and from disk and the SGA as needed. Surely if all of the data is in a huge Oracle SGA so that no disk IOs are required, then Oracle would be as fast as TimesTen In-Memory Database?
Even in this best case scenario when Oracle has cached all of the data blocks in the SGA, TimesTen can still be significantly faster. How does it do it?
In the following latency benchmark, an Oracle DB with and without the use of TimesTen Application Tier Cache are compared:
For latency benchmarks, smaller is better. You can see that even when all of the Oracle data blocks were cached in the SGA that the TimesTen latency was significantly less. This was the perfect apples to apples comparison:
Disclaimer: these are my personal thoughts and do not represent Oracle's official viewpoint in any way, shape, or form.