Database Reference
In-Depth Information
system will start using the swap space (swap file) at the operating system level, which res-
ults in degradation of system performance. Different profile parameters are used to set up
the memory areas discussed here and will be covered in the subsequent sections of this
chapter.
SAP Memory Allocation Sequence for Dialog Work Activity
The memory allocation sequence for a dialog work process is as follows. This allows the
best utilization of memory for user context switching:
•
First
The roll area is used.
•
Second
Extended memory is used (user quota ensures no single user uses all of it).
•
Third
The rest of the roll area is used.
•
Fourth
The heap area is used.
If the dialog work process reaches the fourth stage and does not get completed, it reaches
a stage referred to as PRIV mode. If many dialog work processes enter the PRIV mode sys-
tem performance will seriously degrade for the rest of the users. The system parameters
should be tuned so that this condition is minimized, particularly in the production systems.
SAP Memory Allocation Sequence for Background Work Activity
In the case of background work processes, the memory allocation sequence is a little differ-
ent. Because of this allocation strategy, background work processes will not time out and
will help execute long-running jobs:
•
First
The roll area is used.
•
Second
The heap area is used.
•
Third
The rest of the roll area is used.
•
Fourth
Extended memory is used (user quota ensures no single user uses all of it).
SAP Buffers
SAP buffers are allocated at the application level and are governed by profile parameters re-
lated to different kinds of buffers, such as table buffers and program buffers. Keeping the
data at the application-level buffers and not having to go to the database level will provide
significant performance benefits to the system. But at the same time, not all types of data
should be buffered. For example, while it makes sense to buffer data that is static, it will not
be helpful if the data gets changed frequently. In subsequent sections of this chapter a de-
tailed list of SAP buffers and recommended parameters will be provided.
