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Category: Availability Groups

Cross-Platform SQL Server Availability Groups

Published 2022-08-11 by Kevin Feasel

Rajendra Gupta shows how to set up an Availability Group in SQL Server which runs on both Windows and Linux:

Microsoft supports SQL Server on Linux, and it has many of the same features as the Windows version. You can restore databases from Windows to Linux SQL or vice versa. The Linux SQL works with Red Hat, Ubuntu, SUSE enterprise, Kubernetes containers, and Docker.

Windows-based SQL instance supports SQL Server Always On Availability Groups for high availability and disaster recovery. If you are not familiar with Windows AG configuration, refer to the extensive series on Always on Availability Group (Toc at the bottom).

If you have both Windows and Linux SQL Server, is it possible to configure an availability group between them? Let’s explore this in this article.

This example uses async mode, which is the easier one to set up. With synchronous, you’re probably looking at using Pacemaker to sort out AG status.

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Thoughts on Contained Availability Groups

Published 2022-05-30 by Kevin Feasel

Allan Hirt is quite happy with contained Availability Groups:

All SQL Server availability features except Always On Failover Cluster Instances (FCIs) have a “problem”: when a secondary replica/warm standby/mirror (the term is different for each feature …) takes over as the new boss, some items such as SQL Server Agent jobs, instance level logins, etc., are not there. Going back to the early days of SQL Server when log shipping was not even in the product, this was always a manual process. There are multiple ways to approach this challenge and I am not going to detail them. This “problem” is a longstanding pain point with those who are responsible for managing SQL Server.

Contained AGs solve this issue by having their own master and msdb databases synchronized as part of the AG mechanism.

Click through to see how.

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Seeding AG Replicas from Snapshots in SQL Server 2022

Published 2022-05-27 by Kevin Feasel

Anthony Nocentino is excited about using storage snapshots in SQL Server 2022:

But what if I told you that you could seed your Availability Group from a storage-based snapshot and that the re-seeding process can be nearly instantaneous?

In addition to saving you time, this process saves your database systems from the CPU, network, and disk consumption that comes with direct seeding and using backups and restores to seed.

This process described in this post is imlemented on Pure Storage’s FlashArray and works cloud scenarios on Pure’s Cloud Block Store.

Click through to see how.

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Contained Availability Groups in SQL Server 2022

Published 2022-05-25 by Kevin Feasel

Sean Gallardy is intrigued:

SQL server 2022 (SQL Dallas) has added what is called “Contained Availability Groups”, coming as a nice surprise to many DBAs or other admins out there (incidental DBAs, small shops, etc.) which *could* severely remove a large chunk of administrative overhead and challenges. There’s quite a lot to like about them, but like all things in life there are also some drawbacks that one needs to be aware exist, while these are a giant and amazing step forward for AGs, much like any other tool it has its place and time.

Definitely read the pros and cons of this before giving it a try in the 2022 preview.

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Backups from Secondary Replicas in SQL Server

Published 2022-02-15 by Kevin Feasel

Brendan McCaffrey offers up some guidance:

With Availability Groups there has always been a common theme across the industry to offload your database backups to a secondary replica. It sounds great in theory. I know people that have done this. I also know people that “thought” they were doing this. But the question is, should you be doing this?

Your scientists spent so long figuring out if they could that they forgot to ask if they should.

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Change Data Capture and Availability Groups

Published 2022-02-04 by Kevin Feasel

Jeff Iannucci raises job awareness:

If you’ve ever had to implement Change Data Capture (CDC) for a database in an Availability Group, then you know that the CDC jobs don’t really consider the Availability Group. The capture and cleanup jobs created are set up as if the database exists only on a single instance.

And that’s a problem, because I would guess quite lot of databases are in Availability Groups. Maybe even some of yours. If you have this issue, I’ve put together a step-by-step solution in this post.

Click through for the Microsoft way and the Jeff way.

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Database Mirroring Compatibility and Availability Groups

Published 2022-01-24 by Kevin Feasel

Sean Gallardy checks out the past:

Around 2005, mirroring was born. It was an evolution on log shipping, which is taking log backups, moving them around, and restoring them all in an automated fashion to different servers. Mirroring upped that game and created a dedicated network channel between servers (you could only have 1 principle and 1 mirror, so 2 total) so that there wasn’t this funny business of copying and restoring, additionally it allowed the mirror server to be a highly available copy with automatic failover. Since Microsoft marketing is terrible at naming things, it was originally called, “Real Time Log Shipping” which was then changed to “Mirroring” and in typical fashion you can find the unofficial “Real Time Log Shipping” name all over the place where it was never updated. (I can’t really blame them here, though, it’s hard to find all the little places you’re putting this moniker in and then having some other team tell you to change it all at some way later point)

Read the whole thing. It’s a fun read, a little sad, and helps us understand a bit of availability group behavior which might bite the unaware. I will definitely defend Microsoft’s backward-compatibility emphasis. This makes life so much easier for developers than a lot of other languages and environments. In the R and Python worlds, breaking changes are the norm, meaning that when you update packages, you can expect something to break and now that “20-minute” package upgrade ticket becomes 3 days of trying to sort out what went wrong.

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Creating an Availability Group on Linux in Azure with Pacemaker

Published 2021-12-02 by Kevin Feasel

Andrew Pruski slams in all of the exciting nouns:

There are new Ubuntu Pro 20.04 images available in the Azure marketplace with SQL Server 2019 pre-installed so I thought I’d run through how to create a three node pacemaker cluster with these new images in order to deploy a SQL Server availability group.

Disclaimer – The following steps will create the cluster but will not have been tested in a production environment. Any HA configuration for SQL Server needs to be thoroughly tested before going “live”.

Click through to see how.

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Index Usage across Replicas

Published 2021-11-17 by Kevin Feasel

Jess Pomfret does the math:

Last week, I was working on a project to analyse indexes on a database that was part of an availability group. The main goal was to find unused indexes that could be removed, but I was also interested in gaining an overall understanding of how the system was indexed.

Unused indexes not only take up disk space, but they also add overhead to write operations and require maintenance which can add additional load on your system.  We can also use this analysis to look for a high number of lookups which could indicate we need to adjust indexes slightly.

Click through to see how you can connect together index usage stats from the primary and secondary replicas of an availability group.

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