Task queue of size 1 for serial processing

Question

I want a serial queue where only one task may process at a time. This is my declaration in queue.xml:

<queue>
    <name>pumpkin</name>
    <rate>20/s</rate>
    <bucket-size>1</bucket-size>
    <max-concurrent-requests>1</max-concurrent-requests>
</queue>

Does the "rate" parameter have any effect in this setup?

I want tasks to queue up and only process one at a time.

Thanks

Answer 1

The queue rate and bucket size do not limit the number of tasks processes simultaneously. See this answer which captured a (now gone) official explanation of these configs better than the (current) official docs (you may want to revisit your configs accordingly): https://stackoverflow.com/a/3740846/4495081

However your max-concurrent-requests should ensure only one task is executed at a time, according to the docs:

You can avoid this possibility by setting max_concurrent_requests to a lower value. For example, if you set max_concurrent_requests to 10, our example queue maintains about 20 tasks/second when latency is 0.3 seconds. However, when the latency increases over 0.5 seconds, this setting throttles the processing rate to ensure that no more than 10 tasks run simultaneously.