Scalar Function Single-Threadedness

Erik Darling has another blog post showing that scalar functions inside computed columns are a very, very bad thing:

The first couple times I tried, the DBCC check never went parallel. Since I’m on my laptop, and not a production server, I can set Cost Threshold for Parallelism to 0. You read that right, ZE-RO! Hold onto your drool dish.

Friends don’t let friends write scalar functions.

Related Posts

Risks Of Using Resource Governor To Set Max DOP

Joe Obbish builds an example where Resource Governor’s CPU cap can actively harm query performance: I uploaded the query plan here if you want to look at it. This type of scenario can happen even without Resource Governor. For example, a compiled parallel query may be downgraded all the way to MAXDOP 1 if it can’t get […]

Read More

When Table Variables Have Realistic Estimates, Unrealistic Results May Occur

Milos Radivojevic wraps up a series on deferred compilation for table variables by looking at a hack which used to work but no longer does: With this change, the query is executed very fast, with the appropriate execution plan: SQL Server Execution Times: CPU time = 31 ms,  elapsed time = 197 ms. However, the LOOP hint […]

Read More

Categories

January 2016
MTWTFSS
« Dec Feb »
 123
45678910
11121314151617
18192021222324
25262728293031