Memory managemnt concept

Question

Hi all,
Does any one have any doc about this issue ? (not online help)
I am confuse at the term "SAP Roll Area","SAP Extended Memory","Private Memory"
Regards.

Answer 1

Hi,
When a dialog workprocess sart executing a task given by a dispatcher, it happens
in different steps and accordingly the memory allocation takes place as per the
request of user.
Roll Area, Extended Memory and Provate Areas are the part of this memory allocation.
Lets start with Roll Area.
In the course of their work in dialog work processes, users
accumulate various pieces of data, "user context". The copy action of the user context in the roll area into the local memory of the work process called roll-in. When the request gets completed by the user the user context gets rolled out from the wrkprocess.
If buffer space available the roll area or paging area helds in the particular instance or else they must be stored in physical disk files known as Roll File or Paging File.
Extend Memory:
User Contexts are stored in buffer or in File as they need less memory but when a transaction start executing, it may need  more memory so in that case Extend Memory
comes into picture.
Its  a large area of memory shared by all work processes can
be accessed through pointers.
Main Reasons for using Extended Memory:
1.Fast context switches are needed in SAP systems, because many users share
few work processes
2. SAP transactions consist usually of more than one step/screen
3. Fast context switches are not possible by storing huge amounts of
transactional data in the roll/paging area
4. Extended Memory is accessed through pointers, therefore fast context
switches are possible
Private Mode:
A dialog process that was forced to allocate SAP heap memory automatically
enters PRIV mode. While a user is in a transaction which caused the dialog work
process to enter PRIV mode, no other user can access this process. Since SAP
architecture uses a limited number of work processes to satisfy a larger number of
front end users, other users suffer when a work process goes into PRIV mode. If
several work processes go into PRIV mode simulataneously, they can work well,
but other users can hardly work at all.
Always the PRIV mode is avoided.
Roll Area and Heap Memory(PRIV Mode) are stored in local memory where as the Extended Memory stored in Shared Memory.
If you need more details about these paramaters please let me know.
Thanks,
Tilak