Compute Scalar Functions
Functions, functions, functions
sp_BlitzCache warns about two things:
- UDFs
- CLR UDFs
For Regular UDFs
There can be serious performance consequences when using Scalar and Multi-Statement Table Valued Functions.
- Inhibit parallelism
- Run once per row returned
- Cause poor cardinality estimates
You may even see these warnings alongside a warning for Forced Serialization.
Read more here:
Are SQL Server Functions Dragging Your Query Down?
Still Serial After All These Years
Another Hidden Parallelism Killer: Scalar UDFs In Check Constraints
Another reason why scalar functions in computed columns is a bad idea
For CLR UDFs
They don’t have nearly as many problems, as long as they’re not marked as performing data access. Then they have all the same problems.