PCKCACHESZ is a database configuration parameter which defines how much memory DB2 has available for storing packages and recently executed dynamic SQL. An SQL statement which is present in the package cache memory need not be re-loaded from the DB2 catalog (static SQL) or re-prepared (dynamic SQL).
PCKCACHESZ memory is drawn from DBHEAP memory. If the PCKCACHESZ is too small relative to the demand for concurrent execution of SQL statements, a package cache overflow can occur. Overflows draw upon "reserve" memory and slow down SQL performance.
If the number of "Pkg Overflows" is greater than zero, the size of the PCKCACHESZ should be increased by 10% increments until Package Cache Overflows stop occurring.