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Category: Availability Groups

Low-Downtime Migration Techniques from SQL Server 2017 to 2022

Published 2024-06-17 by Kevin Feasel

Yohei Kawajiri describes three techniques for performing a SQL Server migration:

It is possible to configure a SQL Server Always On availability group with a primary replica running on SQL Server 2017 and a secondary replica running on SQL Server 2022, but there are important considerations and limitations to keep in mind: 

  1.  Backward Compatibility: SQL Server supports having replicas on different versions, but the primary replica must be on an older version than or equal to the secondary replicas. Therefore, having SQL Server 2017 as the primary and SQL Server 2022 as the secondary is valid. 
  2.  Database Upgrade Path: When you decide to upgrade the primary replica to a newer version, you need to follow a specific upgrade path to ensure minimal downtime and data integrity. 

Building an availability group? Yeah, makes a lot of sense. Performing log shipping? Sure, I could see that working. Database mirroring? I did not expect to read that one, mostly because it’s been deprecated for a decade.

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Contained Availability Groups in SQL Server 2022

Published 2024-05-24 by Kevin Feasel

Rich Benner talks about a new feature:

SQL Server 2022 introduced of a number of new features, and one of the more interesting of these is Contained Availability Groups. These are very close to normal Availability Groups, but they have some very important differences. In this post, I’ll compare the new features included and some of the pitfalls that we’ve come across with their implementation.

Read on to learn more about the functionality and several harsh limitations.

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The Risk of Query Failure on Readable Secondaries in SQL Server

Published 2024-02-22 by Kevin Feasel

Kendra Little explains a problem:

If you use readable secondaries in Availability Groups or Read-Scale out instances in Azure SQL Managed Instance, you may have queries fail repeatedly if there is a glitch and statistics are not successfully “refreshed” on the secondary replica. Those queries may keep failing until you manually intervene.

This has been the case for a few years, and it’s unclear if Microsoft will fix this. There is a well established support deflection article which documents the issue and provides ‘workarounds’.

Read on for Kendra’s thoughts. I haven’t run into this before, myself, but I also don’t tend to make very heavy use of readable secondaries.

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Working around a Contained Availability Group Error

Published 2023-12-05 by Kevin Feasel

Sean Gallardy talks about an error:

Contained Availability Groups are the most recent update to the Availability Groups feature, and a great update at that! They are completely new in SQL Server 2022, and like any new feature (or even mature ones) there will be some bugs. Enter in some Access Violations (AVs) that may occur when creating a new contained availability group.

Read on for an example of the error and what you can do until Microsoft fixes it.

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Failed to Update Replica Status Due to Exception 35222

Published 2023-11-24 by Kevin Feasel

Sean Gallardy troubleshoots a problem:

Read Scale Availability Groups can be pretty useful in the right places and for the right things and were a latest feature update for AGs until Contained AGs came along in 2022. Read Scale AGs don’t integrate with clustering of any type and they behave somewhat as mirroring used to where there is no real coordination of resources and it is up to the administrators to make the proper judgement calls or automate whatever possible scenarios they deem important.

Read on to see what this error means and why it’s less of a problem than it first appears.

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Deploying SQL Server with Availability Groups via HPE Serviceguard for LInux and Ansible

Published 2023-11-06 by Kevin Feasel

Amit Khandelwal packs a lot into a post:

It’s time for a new blog on how Ansible can simplify SQL Server deployment, configuration, and availability. If you’ve read my previous blogs on Ansible for SQL Server installation and configuration, and the pacemaker-based Always On availability group, you know how powerful Ansible can be. Now, let’s talk about HPE Serviceguard for Linux (SGLX), a high availability/disaster recovery solution that provides business continuity for critical applications like SQL Server.

Deploying SQL Server Always On availability groups on HPE SGLX is a fully supported solution for production workloads.

Today, let’s look at how you can configure Always On availability group based on HPE SGLX via Ansible. We have collaborated with our friends in HPE to enable the Ansible based deployment for HPE SGLX with SQL Server. This feature is now available for HPE SGLX 15.10. For this demonstration, you can download the evaluation bits from the ‘My HPE Software Center‘. The Ansible bits with the scripts are available on GitHub: 

Read on for instructions and what you need to make it all work.

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Scale-Out Read-Only Databases in Azure SQL DB

Published 2023-09-06 by Kevin Feasel

Etienne Lopes begins a new series:

“As part of High Availability architecture, each single database, elastic pool database, and managed instance in the Premium and Business Critical service tier is automatically provisioned with a primary read-write replica and one or more secondary read-only replicas.”

Read on to see how you can add support for read-only, scale-out replicas to an existing Azure SQL Database. Just know how much that bill is going to be.

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