* Row cache: Commonly called the dictionary cache, tuning of this cache was automated starting in Oracle 7. The row cache caches Oracle's data dictionary rows (not blocks). Objects like sys.tab$, sys.col$, and sys.auth$ are cached within the shared pool's row cache, rather than in the buffer cache. While Oracle must retrieve an entire block to retrieve a single dictionary table row, the result is significant memory savings and a highly efficient cache. In fact, the row cache can be monitored through the v$rowcache view and typically has an extremely high cache hit ratio of around 99%. While DBAs were initially concerned about Oracle removing manual optimization control, Oracle has done a fantastic job at dictionary object cache management.

* In-memory undo (IMU): This was introduced in Oracle Database 10g Release 1. It increases DML and read-consistent-intensive operational performance by keeping as much undo as possible using in-memory objects, instead of traditional undo segments. My tests have shown a 21% CPU consumption reduction when using IMU with a read-consistent-intensive load.

The cursor is a fundamental object that is a complete executable representation of a SQL statement or a PL/SQL programmatic construct, which can be used and reused by any authorized session. Cursors must be created, locatable (that is, found by a search), destroyed (deallocated), invalidated, and reloaded. If any part of the cursor is not in the shared pool and is needed for any reason, that aspect must be reloaded, which does slow performance.