Category: Availability Groups

Cody Konior stress tests Availability Group round-robin routing:

I’ve been hearing about round-robin read-only routing ever since SQL 2016 came out but whenever I tried to test if it’s working it never seemed to be. But now I know exactly how it works and there’s a few loopholes where it may not trigger, and they’re not the documented ones you’re thinking of.

To test the limits of it you’re going to need:

• PowerShell 5.1
• Pester 4 (Install-Module Pester -Force)
• DbData (Install-Module DbData -Force)

I’ll explain any of the Pester and DbData bits along the way so don’t worry. They’re minor framework stuff.

There’s some good stuff here around connection pooling, so check it out.

David Fowler has a quick stored procedure to figure out to which availability group a particular database belongs:

If you happen to be managing SQL Servers with a large number of databases and availability groups, it can sometimes be difficult to keep track of which database belongs to which availability group.

sp_WhatsMyAG will tell you just that.  You can either provide it with the database name and it’ll tell you the AG that your specified database belongs to or you can leave the parameter NULL and you’ll get the AG of the database whose context you’re currently in.

Click through for the script.

Ginger Keys troubleshoots a connectivity failure in a two-node Availability Group:

The AlwaysOn Health Events were consistent with the SQL Server Logs. I discovered that the Windows Server Failover Cluster had been down (but was back online), and that the AlwaysOn Group had failed over and back. But the culprit to my secondary replica and databases being disconnected was an endpoint issue. I found in my SQL Server logs the service account running AlwaysOn had for some reason lost its permissions to connect to the endpoint:

Click through for the entire troubleshooting process as well as the solution.

Tracy Boggiano has some advice on configuring and monitoring distributed Availability Groups:

Monitoring can be tricky with distributed AGs because of the way it shows up in SSMS.  The distributed AG created on the primary AG does not have the ability to show you a dashboard to monitor traffic like the typical AG and the secondary replicas do not even show the distributed AG.  So, to monitor the distributed AG you are best to head to the DMVs.  DMV sys.availability_groups has the is_distributed column that will allow you to only see the distributed AGs.  Below is a query adapted from the Microsoft Docs query to add additional information to check on the status of the distributed AGs which you must run on the primary AG.

Click through for more details.

Sean Gallardy shows a good use case for Availability Groups in scaling out reads:

Read-Scale availability groups are ones where we don’t want the availability group for high-availability or disaster recovery, instead, we want to use it to create multiple copies of our databases that span across multiple servers allowing for the spreading of a large read-only workload. There are various scenarios where this might be extremely valuable and in previous versions of SQL Server it was possible, though there was a requirement of using Windows Server Failover Clustering (WSFC). Read-Scale availability groups do not require the WSFC component and does not give high-availability or disaster recovery, it only acts as a mechanism (availability groups) to facilitate the synchronization of the databases across multiple servers.

To reiterate, this is not used for high-availability or disaster recovery but instead to scale your databases across multiple servers for read workloads.

The remainder of the post shows how to set up an Availability Group without the corresponding Windows Server Failover Clustering components.