Was ich darüber gefunden habe:

The SQL Plan Cache is cleared during each IPL. The Plan Cache is a repository that contains the access plans for queries that were optimized by SQE. The Plan Cache is interrogated each time a query is executed in order to determine if a valid access plan exists that satisfies the requirements of the query. If a valid access plan is found, it is used to implement the query. Otherwise a new access plan is created and stored in the Plan Cache for future use.