Run flows one after another
Quiz question
What happens to new trigger events with a parallelism of 1?
Solution
- A) They are discarded immediately and never runWrong. New trigger events wait. Whether each one becomes a run is only uncertain once the queue is full.
- B) They wait until the current run has finishedCorrect. Further runs wait in a queue and start one after another.
- C) They still run in parallel, just more slowlyWrong. With a parallelism of 1, exactly one run is active at a time, all others wait.
What it is about
An automated flow starts on every new event, even if the previous run has not finished yet. When two runs work on the same data at the same time, you get duplicates, or one run overwrites the other. In the trigger settings you turn on Concurrency Control and set the degree of parallelism to 1. Then only one run is active at a time, further runs wait and start in order. That costs time but protects the data. The queue is limited: at most 11 runs can wait. And think before you do it: you can only turn off Concurrency Control on the trigger by deleting the trigger and adding it again.
When to use it, when not
Use it
When several runs work on the same list, the same file or the same counter.
Better not
When a large number of events arrive in a short time. The queue is limited, and one run after the other becomes a bottleneck.
Most common mistake
Turning on Concurrency Control on the trigger just to try it out. The only way back is to delete the trigger and add it again.
License
Standard Runs without a premium connector, so the license from Microsoft 365 is enough. Source on Microsoft Learn: Power Automate licensing FAQ. For your whole flow: License check.
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Short link: powerautomate.ninja/en/35
Source: PowerPlatformTip #35, Microsoft Learn: Limits of automated, scheduled, and instant flows.