To protect the system from running out of resources due to a large number of data flows that run simultaneously, you can indicate the maximum number of data flow runs for a given node type, as well as change the maximum active runs threshold at run time. For more information, see Data flow run limits.

By setting data flow priorities, you can specify the importance of each data flow in a given data flow service type. Data flows are executed automatically, according to two factors:

• The relative importance (priority) of the run that you can set to Low, Medium, or High.
• The order of submission (activation time) of the run.

The runs that cannot execute when triggered by the user or system event (for example, low priority runs or runs that exceed the set data flow service limit) are queued automatically. The data flow service attempts to schedule the queued runs of equal priority in the order of submission, from the earliest to the latest. When the resources become available, then the oldest highest priority run starts. If the run is completed, stopped, or fails, then the current oldest run with the highest priority moves to the front of the queue. If the data flow service can perform a run with a higher priority, then the lower priority runs will remain queued.

For example:

Consider a scenario where the data flow service limit is set to five runs and all runs are currently in progress.

1. The data flow service analyzes the run priority first, and then analyzes its activation time. When the limit of five active runs is reached, a new run (DF-6) with a medium priority level starts instead of the DF-2 run which has the lowest priority and has been added most recently. Another newly added run (DF-7) has a low priority level, therefore the run is queued.

   

2. If you add another run with a higher priority (DF-8), that run starts first, while the DF-6 run moves to the queue.

   

3. When the highest priority active run finishes (DF-3), the data flow service automatically starts the next highest priority, earliest run from the queue (DF-6).