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Purpose

This Wiki explain about SAP load info messages feature.

Overview

As from kernel 740 the SAP system has a feature to avoid overload situations in the request processing. This feature uses load info messages to keep the entire SAP system (all remote Application Servers) aware of its application server load situation.

How it works

The load calculation is designed to avoid overload of dispatcher queues. An example of an overload situation is about the update requests. If, for example, an application server is handling long update requests and further requests began to increase the update queue, this application server should no longer receive update requests before return to normal load situation.

The load calculation is able to identify such situation and inform the update mechanism to stop to send update requests to this application server deactivating its update processing.

 

Note that the deactivation of update mechanism in this Application Server is temporary. This occurs until it is overload and this deactivation does not occurs if no other update server available to process updates.

 

The parameter rdisp/high_load_quota controls the trigger to send the load info message and its default definition is "load=90, queue=5"

The "load" and "queue" are thresholds used to determine when to trigger the load info message. Every second the dispatcher calculate the % length of dispatcher queue and compare with "queue" and the % of Work Process utilization of this Work Process type and compare with "load".
See further information about this parameter in the RZ11 documentation.

In SM50 it is possible to see the average load values in the last 1,5 and 15 minutes:

 

In case of reach these both thresholds, the service of this worker type is overload and dispatcher inform all others servers by sending a load info message.

In case of an overload in UPD and UP2 worker type, the dispatcher will log the following information in the dev_disp trace.

DpSendLoadInfo: quota for load / queue fill level = 11.700000 / 5.000000
DpSendLoadInfo: queue UPD now with high load, load / queue fill level = 11.704559 / 0.000000

 

This will deactivate the update mechanism in this specific server, in case of others servers available to process update requests, and in SM14 (servers tab) it is possible to notice such situation. At the moment load fall below the threshold values a load info message is send again and the update is activated.

DpSendLoadInfo: queue UPD no longer with high load

 

Conclusion

Currently, the update mechanism use the load information to control the dispatching of request, however, it is expected that others dispatches mechanisms also implement this feature.
This feature is powerful to improve the stability of SAP Application Servers.

 

Related Content

Related Documents

Related SAP Notes/KBAs

2187985 Update server randomly gets deactivated