Question

At SharePoint Saturday in Lisle, IL this weekend, Robert Bogue said there’s a difference between active and running workflows. I’ve looked on the web, but can someone clarify?

If I can have up to millions of active workflows on the server, why can I only have 15 or so running workflows per server?

Answer 1

Yes, there is a difference:

• “Running” Workflows are all which currently are doing something (i.e. executing an activity).
• “Active” Workflows are simply all which are “running” but currently are not doing anything – e.g. waiting for OnItemChanged or DelayActivity.

The key to understand this is WorkflowEventDeliveryThrottle (here for SP2007, because the documentation for 2010 doesn’t exist). The standard value for this is property is 15. That means that there are only 15 concurrent workflow which can run at the same time. After this limit is reached the workflows get queued to the OWSTimer which executes the workflows after some arbitrary time (I think the workflow timer job is set to every 5 minutes).

This Throttle can be changed by using stsadm (AFAIK Powershell doesn’t work – you can change the property via code of course setting SPWebService.WorkflowEventDeliveryThrottle):

stsadm -o setproperty -pn workflow-eventdelivery-throttle -pv "20"

Now the maximum number of “running” workflows (better would be “maximum number of workflow events that can be processes simultaneously”) would be 20. See some other SO post where someone plays with the parameter.

There is a nice technical blog post to understand Workflow Event Processing: About the “workflow-eventdelivery-throttle” parameter.

Similar to the throttle is the WorkflowEventDeliveryBatchSize which denotes the maximum number of workflow events that are processed in a batch.

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Summary:

• You can have thousands of active workflows, e.g. all waiting for the workflow item to be changed. They are not running, not finished – simply active.
• There is a limited number of workflow events that can be processed at the same time (you called it “running” workflows)
• You could also have thousands of running workflows, e.g. all of them might get triggered by a delay activity set to 5 minutes, but only a limited number of them is running simultaneously, the rest of them gets queued for later execution.