SQL Server 2019 Cumulative Update 6: The CU6th Sense

The 6th Cumulative Update for SQL Server 2019 is out, and she’s a big one. In keeping with the questionable design decision from CU5, Microsoft has given up on documenting a lot of this stuff, and they’re giving you “bug reference numbers” that correspond to some internal documentation somewhere that you’re not allowed to see.

That, dear reader, strikes me as a Bad Idea™ for a relational database that you’re trying to build a business on.

Instead, you’re just left to guess as to what this stuff means, whether it’s relevant to your workloads, and what changed behaviors you should look out for when you patch:

• Fixes an unexpected result issue for variables when you use multiple variable assignments from select statement that has scalar UDF inlining. After you apply this update, SQL Server blocks UDF inlining in special cases of select-with-assignment queries.
• The external satellite processes in SQL Server have a restriction to not use more than 8 cores on the system for satellite worker threads, but in case of highly parallel execution all the process are restricted to same set of 8 cores on the machine and don’t use the other cores available on the system. This issue only happens on Windows and slows down highly parallel queries. The fix is to allow the processes to use 8 cores rather than the fixed set of cores on the system
• Fixes high CPU consumption on Availability Group secondary database when using multiple redo threads and uninitialized LSN, leading to extra reads under some rare scenarios
• Fixes access violation exception that occurs when plan cache involves sys.dm_hadr_ag_threads and sys.dm_hadr_db_threads DMVs
• Fixes an access violation error that might occur when auditing commands that require password masking
• Fixes an issue with an orphaned spinlock due to access violation and results in the repeatedly printed in messages log: “getspinlock pre-Sleep() after AV”
• Fixes issue with access violation exception when you execute query with UDF and multiple grouping. After applying this update, SQL Server blocks UDF inlining if group by includes multiple groupings. (Strangely, this is filed under “SQL performance – Linux” which makes me wonder if Linux scalar inlining now works differently than Windows? Sure wish I had a KB article to click on to get more details, but I guess that’s too much to ask for.)
• This update contains an improvement for XML Validation in SSIS XML Tasks. This improvement allows validation of INCLUDED schemas in XML task.
• Fixes errors that occur in SCOM 2019, when you upgrade from SQL Server 2016 or 2017 to SQL Server 2019 CU5 with UDF inlining ON

So, uh, here it is, and good luck. I’m sure it’ll be fine.