Pushing the Limits of AGs Many of you reading this likely have an Availability Group (AG) set up on at least one database in your organization. Maybe not most, but many of you as this has proven to be a technology that many people like for HA/DR, upgrades, and probably other uses. As the technology has evolved from it's SQL Server 2012 debut, it has improved in many ways. This might be one of the few features that has received regular attention from the developers in Redmond across multiple versions. That's not to imply this is a foolproof or bug-free feature. Numerous people have had issues with the various types of AGs. From setup to performance to scale, I've seen many people post questions and search for answers on how to get their system running smoothly and reduce any late-night calls. Over the last decade I've seen various people test different parts of the AG technology, but not many pieces about how much you can stress the technology at high levels. Microsoft supports up to 8 replicas, but what about groups and databases? The recommendation page says MS has tested 10 AGs and 100 databases, but nothing else. I ran across a post on LinkedIn from Calin Oprea that covers his AG testing. He hasn't written about it, but says he can make the scripts available. He tested 50,000 databases, maybe more. He says 50k+ in the post and notes anything beyond 500 databases per instances starts to fall apart and 1000 seems to be a hard limit. Failover doesn't work, even without a workload. That's quite a test of the technology at it's extreme. I've never run more than a few AGs or databases, and I see people posting and talking about dozens. Most of the people I know doing things at scale are using less than 10 AGs and usually no more than 100 databases max. I wonder how many of you out there use more than 2 AGs on any instance and more than 20 databases. I'm sure there are lots of systems at this scale or larger, but I'd guess the majority are 1 AG and less than 10 databases. Take a look around your environment today and see what the average and extremes are for Availability Groups. And if you've never looked at them, it's a piece of technology you ought to become familiar with. HA/DR is becoming a base requirement in many situations and it's available in the cloud with the toggle of a setting. If you work on premises, it's likely your clients expect your systems to easily failover to another location. Check out Stairway to Always On to get started. Steve Jones - SSC Editor Join the debate, and respond to today's editorial on the forums | 
