One of the mostexpensive operation a Oracle Database can do, is to read the data from the disk. On the other side, read a block from the memory is one of the goals in Database Performance Tuning. In the past Oracle has introduced some feature that can help the DBA to prevent Disk Reads (for example Smart Flash Cache).

Normally a Oracle database decides what data to cache in the buffer cache. For example when there is not enough room the database age out blocks from the cache. Other operations like a Direct Path Read complete bypass the SGA and loads the blocks into the PGA. Prior to Oracle 12c a DBA can use the KEEP Option to prevent the aging blocks from the buffer cache.

Beginning with 12cR1 (12.1.0.2) Oracle introduces a new Feature called FORCE FULL DATABASE CACHING. This Feature allows that the DBA can tell the database…