Latest blog posts

Should You Use SQL Server Readable Secondaries if Queries Can Fail Repeatedly at Any Time?

By Kendra Little on February 21, 2024

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’.

As a user on StackExchange wrote in September of 2022, “This is an outstanding bug in SQL Server which has been ignored for quite some time, unfortunately.” Based on a link provided in that post, it appears that feedback was provided for this as far back as SQL Server 2012, when AGs were introduced.

Just how viable are readable secondaries / scale-out read servers for production use if it’s acceptable for queries to fail at an undocumented/unknown rate?

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Ugly Bug: SQL Server Online Index Rebuild sometimes happens offline without warning

By Kendra Little on February 7, 2024

I found a nasty bug in SQL Server and Azure SQL Managed Instance recently: sometimes an “online” index rebuild of a disk-based rowstore clustered index (basically a normal, everyday table) isn’t actually “online”. In fact, it’s very OFFLINE, and it blocks both read and write queries against the table for long periods.

If you manage to make it through a rebuild successfully, the problem goes away for future rebuilds of that clustered index – likely leaving you bruised and bewildered.

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Is the Azure SQL Managed Instance Business Critical Service Tier Worth the Cost?

By Kendra Little on January 29, 2024

The Business Critical service tier in Azure SQL Managed Instance is a lot more expensive than General Purpose. For the extra money, you get a different architecture.

Is it worth the extra cost? Spoiler: your mileage will vary, but probably not. Let’s talk about why.

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Azure SQL Managed Instance General Purpose Architecture and Performance/Cost Tradeoffs

By Kendra Little on January 22, 2024

Whether or not you use Azure SQL Managed Instance, you will likely be asked for an opinion on it eventually if you’re a SQL Server person.

While the architecture is documented, it can be a bit of a long read and some of the gotchas are spread out over different pages – so I’m drawing up the architecture of each service tier along with notable implications for the design on performance and cost. Here’s the scoop on General Purpose.

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