Persistent Subscriptions and "Max Subscriber Count"

Quick background: we’ve got a process that consumes events from an EventStore cluster (currently version, upgrade to 5 planned for this summer). The process has a few bottlenecks that hinder performance. It’s being re-written for better throughput, but in the interim, we scale out to handle peak loads.

My question is around the “Max Subscriber Count” on a persistent subscription. The default value is 10. Right now, we’ve got our max set to a count of 20, but we’re thinking we may need to go a bit higher during peaks. We’ve gotten close to 20 during some sustained loads, with no issues detected so far.

I should also point out that this cluster has quite a few other readers across several other persistent subscriptions, though I don’t know any of those other subscriptions that go above 10 subscribers at any given time.

We’re uncomfortable raising the max count above 20 without understanding a bit more about any risks or other potential problems in increasing the count on a single persistent subscription. Are there any recommendations around the maximum subscriber count? Any possible issues with changing the default value? If we decide we need to go higher, is there anything we can or should be monitoring to make sure there are no potential problems on the cluster?

Many thanks.

Robert Goheen

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We have found out that this option wasn’t present there before. The contribution that added the subscriber limit option had the motivation to deliberately limit the number of subscribers. Specifically, the contributor wanted to have no more than one subscriber (I guess he wanted to keep the ordering). Other than that, there should not be a problem to increase the number of subscribers.

Thanks for the clarification. Do you happen to have the commit or issue ID for that addition? I’d be curious to see the discussion around that change.

Thank you.

@pieter.germishuys pointed me to this