If your Logic program is configured to execute On Input Processed (see Define the Execution Method for a Logic Program), you can use the Execution Queue Size setting to define the maximum number of executions that can be placed in a queue. This feature is designed for use with programs that need to perform calculations on values that are reported by outstations.
When an outstation reports values, it reports them in a block (multiple values are reported at once). As a Logic program can only be executed in response to one value at a time, ClearSCADA stores the block of values in a queue, referred to as the execution queue. Any Logic programs that use the values reported by the outstation then use the values in the queue—they execute for each value in turn. This means that Logic programs execute in response to the reported values rather than the current values (some of the current values may have been updated by the time the program is executed).
The Execution Queue Size defines the maximum number of values that can be stored in the execution queue. Typically, the default Execution Queue Size of 250 is appropriate. However, you may need to change this setting if your program is not performing its calculations on the reported values (this often means that there are too many values being reported, and the execution queue is full and so cannot store any new values).
If the execution queue becomes full, any further values reported by the outstation will be disregarded, so if the Execution Queue Size is too small, data could be lost.
To change the Execution Queue Size, display the Logic Program Form, select the Logic tab, then enter the required number in the Execution Queue Size field. We recommend that you do not increase the Execution Queue Size beyond 1000 as doing so may cause the server to run out of memory.
Further Information
Display the Logic Program Form: see Configure an ST Program, Ladder Diagram, SFC or FBD.