A basic metric for system-wide performance is up time, or system availability. Generally, this is absolute time less scheduled outages. There are many manual and automatic ways of tracking this, but one of the simplest, yet most accurate, for an SAP system is theavailable.log.
available.log is stored in the work directory (/usr/sap/<sid>/work). If you don’t have Operating System access, you can also view the file via transaction AL11. Find and select Directory parameter DIR_INSTANCE, then drill down into this directory….
Find the work directory and drill down again,…
… sort the resulting list of files, and availability.log should be at or near the top.
It is written by the SAP service sapstartsrv.exe. The service checks the status of the actual process list (i.e. the entries you see in the MMC SnapIn under the “Process List” node). If all processes are “green” the instance is considered to be available. Since the status information of the Dispatcher is calculated from multiple parameters (process running + connected to message server + shared memory available + good dialog queue time) the information in available.log is very reliable.
The information is checked and updated every 60 sec and at instance startup and shutdown. The default threshold for a “good” dialog time is 5.0 sec. You can adjust this threshold with the profile parameter max_dia_queue_time in the default or start profile (service must be restarted after changing it).
If the service notices that the last update to ‘available.log’ is older than 60 secs (e.g. due to computer shutdown), it will always start a new line in ‘available.log’, for example you may see:
Unavailable 30.04.2009 15:31:35 – 30.04.2009 21:28:47
Unavailable 30.04.2009 21:52:32 – 02.05.2009 08:42:39
instead of
Unavailable 30.04.2007 21:52:32 – 02.05.2007 08:42:39
Because of the time delay required to cause this situation, it is extremely likely that at least one service related to the SAP instance was not running (e.g. caused by computer shutdown).
Currently, no SAP application (that I know of !!) reads available.log – it’s just a simple log file to help measure your system availability.
Caveat: You do need to make sure that all the processes that you would see in the SAP MMC are running correctly for correct values to show in available.log. While experimenting several years ago, I had a situation where the igswd.exe service was not running correctly. I had modified the start profile, but restarted the system incorrectly. Until I did this, which reloaded my profile changes correctly, available.log was reporting that the entire SAP system was unavailable.
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