Data Dictionary Hit Ratio — The ratio of cache hits to cache lookup attempts in the data dictionary cache. In other words, the rate at which the database goes to the dictionary instead of the hard disk to retrieve data. A low ratio suggests more RAM should be added to the system.

Gets — The number of blocks accessed via single block gets (not through the consistent get mechanism).

Cache Misses — The number of accesses made to the block buffer to retrieve data in a consistent mode.