UDFs And Recompilations

Erik Darling shows how to diagnose a high recompilation problem:

So yeah, that function seems to get up to something once for every ID you pass in. Remember that in our STUFF… query, we grabbed the TOP 10 each time. In the XE session, each time we call the proc, the string splitting function compiles and executes code 10 times. Bummerino. That’s the life of a loop.

On SQL Server 2016 (and really, with any non-looping code), we can get around the constant compilations with a simple rewrite. In this case, I’m calling 2016’s STRING_SPLIT function instead of the MSTVF function.

Read on for more.

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