Trace Flags in Azure SQL Database

One of the ways that you take more direct control over your SQL Server instances is through the use of trace flags. There are a number that people recommend you enable by default. Prior to Extended Events for example, I’d say you should turn on trace flag 1222 in order to capture deadlock information on your server (now I just recommend you use the system_health session). I absolutely think you should turn on trace flag 2371 to get better behavior out of your automated statistics updates. There are others that I’ll leave to all the systems experts to advise you on.

What about Azure SQL Database?

I doubt you’ll be shocked, but if I try this:

DBCC TRACEON (2371,-1);

I get the following error:

Msg 2571, Level 14, State 3, Line 1
User ‘xxx’ does not have permission to run DBCC TRACEON.

This error makes sense right? We’re talking about a Platform as a Service (PaaS). You’re only managing the database, not the server, so you don’t have access to control underlying server behavior.

How about if we want to just modify the behavior of a query? You can use the query hint QUERYTRACEON to adjust behavior. For example, the new statistics cardinality estimation engine in 2014 and better is just marvelous. It’s in use in Azure SQL Database. However, there are edge cases where the old way can work better for certain queries. If you want to go to the old cardinality estimation engine in SQL Server 2014/2016, you use traceflag 9481 in a query hint like this:

SELECT  *
FROM    Sales.SalesOrderHeader AS soh
JOIN    Sales.SalesOrderDetail AS sod
        ON sod.SalesOrderID = soh.SalesOrderID
WHERE   sod.OrderQty > 30
AND sod.ProductID = 867
OPTION (QUERYTRACEON 9481);

Bad news. The error message is the same.

Working within Azure SQL Database, trace flags are not a part of your tool set.