This parameter is used to specify the total size of the roll area, in bytes.
The following graphic shows the parameter’s relationship to the initial allocation of roll memory (ztta/roll_first).
A part of this area (in the graphic, roll area 1) is allocated a user context at the beginning. Its size is defined in ztta/roll_first. The partial area is for the data that must be contained in the roll area. When a user context is changed, this data is “rolled” (copied) into and out of a work process. If ztta/roll_area is larger than ztta/roll_first, the additional space makes a second part available (roll area 2).
If the user context cannot be allocated more extended memory, this second part of the roll area is available for the dialog processes (see Allocating Memory for User Contexts).
By specifying a higher value for ztta/roll_area than for ztta/roll_first, you avoid allocating local private memory as soon as the set limits of the SAP extended memory are reached. The remaining roll memory therefore serves as the last buffer before a user context has to allocate heap memory.
This pushes back the point in time at which a work process is switched to PRIV mode (see Private Memory). Although there are advantages with this procedure, there are also some disadvantages: The copying procedure is much slower for storing data in the roll area for changing work process contexts. The copy procedure necessary for the roll area with context changes is slower than the allocation procedure used for context changes with SAP extended memory. Therefore, increasing the roll area memory slows down the context change.
The roll area is not important with 64 bit platforms where sufficient extended memory is available. The default value is platform-specific and is determined dynamically. The default value is specified in transaction RZ11. This value should not normally be changed.
If you still have to make changes on your platform, keep in mind the following dependencies:
· rdisp/ROLL_SHM should be adjusted if you change ztta/roll_area.
· rdisp/ROLL_MAXFS must be adjusted if you change ztta/roll_area.
· ztta/roll_area must be larger than, or the same size as ztta/roll_first.