Database Reference
In-Depth Information
• Shared memory = Allocated at instance start as per SAP extended memory parameter
and related memory areas configuration in instance profile
• Local memory = Allocated on demand and released after use immediately as per SAP
heap area related parameter/s configuration in instance profile
• Local memory is associated with individual work processes (1:1)
• Heap memory = Temporary memory is allocated out of local memory
• Heap memory is allocated when extended memory is full
• Local memory is used for ABAP load, data, local roll area, paging area and so on
• Shared memory is associated with all work processes (1:n)
• Shared memory has different SAP buffers, extended memory, roll buffer, and paging
buffer
• SAP buffers contain global objects for all users and work processes such as programs
and buffered table content
• Extended memory contains unfinished transaction data of application users (1:n rela-
tionship with work processes)
• Roll buffer contains initial user contexts (writes to roll file at file system level)
• Paging memory contains ABAP extracts and exports (writes to paging file at file sys-
tem level)
• User context is defined as memory area that has individual user authorization data and
variables that are associated with that specific user activity in the system
Now that we have looked into the definitions of different SAP memory areas, we will
study the memory allocation sequence in the next section.
SAP Memory Allocation Strategy
By design, SAP serves more users with fewer dialog work processes. The dialog work pro-
cesses achieve this design goal by moving the smaller user context and associated pointers
to the actual transactional data (large memory areas) in the extended memory between the
work processes called as rolling in and rolling out of the user contexts. This process allows
the system to easily switch the smaller user contexts with pointers to extended memory with
larger transactional data between different dialog work processes. The roll area and paging
area, along with the roll file and paging file, respectively, are used for the roll-in and roll-out
processes. Once the roll area and extended memory are used up by a user, the system is
forced to use the on-demand local (heap) memory. If the entire heap memory is used up, the
