1. A multicache system configurable within a primary memory of a host system for improving the performance of a number of processes running on the host system in processing complex database query statements, the multicache system comprising: (a) a plurality of local caches in main memory corresponding to the number of processes being run on the host system, each local cache being associated with a different one of the processes being run; and (b) at least one configured central cache system located in a predefined area of primary memory shared by the processes, the central cache system being operatively coupled to each of the plurality of local cache systems associated therewith, said central cache system including: a number of shared control structures used for controlling access to the central cache system; a number of sets of central cache control structures corresponding to the number of central caches configured for storing code segments; and, a control mechanism operatively coupled to the number of shared control structures and to the number of sets of central cache structures, the control mechanism being operative to control the configuration and operation of each of the central caches so that generated code segments produced by any one of the processes for executing a complex database query statement are stored automatically in the local cache associated with the process and in the central cache configured to be associated therewith for use by other processes associated with the same central cache in processing logically equivalent complex database query statements.