Library Cache contains Shared SQL Area as well as Shared PL/SQL Area.
Shared SQL Area contains the parsed trees and the execution plans.
Shared PL/SQL Area contains the predefined PL/SQL programs as well as user defined programs.
The sizes of Library Cache as well as Data Dictionary Cache is determined by the parameter "shared_pool_size".
Data Dictionary Cache is also known as "row cache".
If shared pool is under sized(not properly sized, it degrades the performance of the application).
