By default, Orchestrator permits 300 workflows to run at the same time. When the Orchestrator server has to run more than 300 concurrent workflows, the pending workflow runs are queued. When an active workflow run completes, the next workflow in the queue starts to run. If the maximum number of queued workflows is reached, the next workflow runs fail until one of the pending workflows starts to run.
By setting system properties in the Orchestrator vmo.properties configuration file, you can control the number of workflows that are running at the same time and the number of pending workflows that are waiting in a queue.