Suppose our server process needs memory for a large cursor. When Oracle is searching for shared pool memory, if the object size is larger than the threshold, Oracle first searches in the reserved area. If the memory is not found in the reserved area, Oracle will check in the nonreserved area. This strategy helps to keep smaller objects out of the reserved area, thereby preserving it for the larger objects.

* The hidden parameter _shared_pool_reserved_pct, which defaults to 5 (for 5%), can be used instead of shared_pool_reserved_size.

* A relatively large object is defined by the instance parameter _shared_pool_reserved_min_alloc, which defaults to 4,400 bytes. Interesting, notice the default threshold value of 4,400 bytes is just larger than the typical single chunk request of 4,096 bytes. So, by default, Oracle is saying that any memory request larger than one typical size memory chunk request is to be considered large and therefore should get its memory from the reserved size.