Hardware Capacity Analysis SAP BASIS

As explained in Chapter, client/server architecture, such as the one SAP systems are based on, several servers might play the role of application servers, and only one is assigned the role of database server. A SAP system is scalable; therefore, you may add application servers, as needed, if the workload increases. It is essential to understand, though, that resources are limited, in particular, hardware resources. In this topic, it is time now to check the capacity of your hardware in terms of physical memory and CPU. Monitoring the hardware consumption of your servers on a regular basis is a best practice that can prevent performance problems due to hardware bottlenecks, if these are detected on time and the proper actions are taken.

The Operating System Monitor

Execute transaction OS06 or choose the menu path Tools | Administration | Monitor | Performance | Operating System | Local | Activity. Transaction OS06 leads you to the same place and transaction OS07 leads you to the selection of remote servers, so you can choose one of them to monitor from where you are. This is especially useful when you have a standalone database server where you do not have a SAP instance and, therefore, you must log on to that server remotely via RFC. You can check the operating system of each server locally or remotely and if you have multiple instances in one server it does not matter where you are logged on, you will always see the same data when you monitor the operating system of that server.

The information obtained in this monitor is collected by a program that runs at the operating system level: the SAPOSCOL (SAP Operating System Collector) is a program with its own versions and patch levels that can be started or stopped independently of the instances. If the collector is not running, "0" values will be displayed in the Operating System Monitor. If the collector is obsolete, wrong values may be displayed. The most important indicators in this monitor are the CPU utilization and the paging activity.

Troubleshooting CPU Bottlenecks

First, we take a look at the CPU activity. The number of CPU's in a server is given by the number next to Count. In addition, the "load average" detailed by the CPU utilization figures below this indicator gives you the number of work processes that have been at some point waiting for a free CPU for 1,5, or 15 minutes. These figures should normally be very low. Otherwise, it is an indication that the hardware is not being optimally utilized. When monitoring the CPU consumption by the users in the system, it is easier to look at the CPU idle indicator (that is, "how much" of the CPU if this was something that we could count is free). As a rule of thumb, this should not go below 20% (that means a total CPU utilization for that server of 80%).

Otherwise, you may risk a hardware bottleneck, if the CPU idle is very low for long periods of time through the day. During peaks of workload you may see the CPU idle go to very low numbers and this may be expected, if you sized your system accordingly. A CPU bottleneck can come from a number of reasons. A simple program can cause a CPU bottleneck, if this is too resource demanding or if it is poorly written. Excessive workload in a server can easily cause a CPU bottleneck and nonoptimal workload distribution as well.

In addition, not only processes related to the SAP software are running in a server. External programs, such as monitoring tools, scripts at the operating system level, scripts on the database server, screen savers, virus scanners, backup tools, and so on may be running at the same time as your online users and occupying the available CPU's in your servers, which may lead your users competing for resources and experiencing performance problems.
In order to check all the processes that are running in a server, you may check so at the operating system level with the proper commands, or from the Operating System Monitor choose Detail Analysis Menu and then Top CPU.

The list displayed shows all the processes running in that server and the CPU consumption related to each process. Programs that are named disp+work are the well-known work processes. In a database server, you may see database processes and in any given server you may see any kind of external processes as well. When external processes are the cause of a hardware bottleneck, the question you need to answer is, "Is that process necessary to run and, if so, must it run at this time, interfering with users?" It is best practice to check whether the workload can be redistributed among all application servers and avoid overload, especially in the database server, because this is a central resource and if this has a hardware bottleneck, all users in a system will be affected.

Troubleshooting Physical Memory

The paging indicators under Memory in ST06 show you the amount of pages going "in" or "out" of physical memory from or into hard disk and therefore it gives you an idea of how well the physical memory is utilized versus the hard disk. Figure shows the indicators of memory utilization in the Operating System Monitor.

Memory utilization figures in the Operating System Monitor

Memory utilization figures in the Operating System Monitor

As a rule of thumb, consider 20% of RAM as the amount of paging that should not be exceeded on a regular basis. Again, excessive workload, nonoptimal distribution of it, resource demanding or poorly written ABAP programs or external processes may contribute to a memory bottleneck. Checking the memory utilization as explained in the section on memory management (in transaction ST03N, Memory Profile, or in ST02, Mode List) helps you to eliminate variables and find out if one of the causes of an excessive memory consumption comes from the users. It is a well important to train the users in an efficient use of the programs and transactions that are available, especially those with large reporting possibilities and selection screens that can. make a difference when executed!

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