Extract Utility User's Guide - Supra - Cincom

Setting the z/OS STACK parameterWhen you code the STACK parameter, you set aside an area of memory calledthe stack/heap for Extract to use. The stack/heap has two areas, theProcedure Call Stack and the Dynamic Memory Heap, as shown in the followingfigure:Stack0(Unused)Heapxxx KAs the figure shows, the stack starts at the beginning of the area. It storessome run-time information and all global variables. In addition, when eachprocedure starts, it allocates an area on the stack to store its local variables,and call and return information.As the procedure calls more nested procedures, the stack grows larger. As thenested procedures return, the stack grows smaller. Thus, the size of the stackdepends on the levels of nesting in the procedure calls, and the number andsize of the procedures' parameters and local variables. As the stack gets larger,it allocates space toward the heap area.The heap is the area that Extract dynamically allocates at run-time. Here,Extract stores internal context information, that is, variables that are notstored in the stack area. When Extract no longer needs the space, it is freed.As an area is freed, it can be reallocated. Thus, this area varies in size. When aprocedure allocates the first heap area, it starts at the end of the space. Whena procedure allocates a new area, it takes the new area from the space closerto the stack. As the following figure shows, when the stack and heap getlarger, the unused space between them gets smaller:Stack0(Unused)Heapxxx KExtract Utility User's Guide, P25-9513-03 26Chapter: 3. Executing the Extract utilitySection: Choosing run-time options in z/OS