Cracking SAP Memory Management _Part1
This blog gives an insight into SAP Memory management. The contents has mainly data from SAP Performance optimisation guides, discussions in internet and most importantly my experience in SAP World. I tried not to do too much copy and paste (In this Internet world nobody can claim authority of their data , correct???, So please tell me if it is reproduced from somewhere else) The blog is my point of view and any different opinions or approaches are welcome .Have fun!!
What is RAM and Virtual Memory?
When we discuss about memory in a SAP Perspective , the first thing comes into my mind is Physical Main Memory (RAM). RAM Is physically available main memory .
Well, we have to consider a bit more we call it virtual memory , The general rule of thumb is RAM and Virtual memory should be in a considerable ratio (I know it is very subjective ) What I mean to say is that there shouldnt be a huge difference . All the processes together cant have more memory than sum of RAM+ Available SWAP SPACE which is almost equal to Virtual Memory .
The conclusion is that you can consider more than RAM in your SAP system .
STOP Here you want o know what is Virtual memory available in your SAP system??
Transaction ST02, Click on storage as per the screenshot
Virtual memory is the sum of local memory and shared memory.
Only one operating process can read or write from this memory.
Shared Memory ?
Shared memory can be accessed by multiple operating system process (In an SAP World shared memory of Work process can be accessed by a work process of the same instance)
We are talking terms of 64bit technology. I am not sure about 32 bit architecture it has to do something about address space and the fragmentation which I conveniently ignore it here. Lets make it simple , most of the systems are 64bit and lets discuss from that perspective. Lets make conclusion here
RAM -Physically Available Main memory
Virtual Memory – More than RAM 🙂 which can be used by all processes
Shared Memory – as it sounds , shared , SAP Buffers reside here
Local Memory- Local to a SAP Work process or Operating system work process
I stop here and get to SAP Terminology which will be based on these base concepts. Have a cup of Coffee Now.