When schould I increase the MaxAGLinkQueueSize parameter from the WinCC OA S7 driver?

The parameter MaxAGLinkQueueSize defines the maximum „active“ parallel read requests from the WinCC OA driver to the PLC.

This means in detail:

Per connection, the WinCC OA S7 driver will reserve the MaxAGLinkQueueSize number of entries in the list of parallel read requests.
Per cycle of the S7 driver, it will look if a poll group has to be requested from PLC.
If yes, he will optimize the read request using the maxGap parameter and the result is a list of read requests which have to be sent to the PLC.
Then the driver will fill the list of read requests until the list is completely filled. These requests are sent to the PLC in parallel. Within the next communication cycle of the PLC, the PLC will answer to the read requests.

The received answers will then delete the read request entry from out read request list.
So within the next driver cycle, the next read requests will be sent out to the PLC.

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So – in standard applications, the recommended value of 1 will be OK, in larger sized applications, the parameter should be in a range from 5-10.