Cost Threshold For Parallelism Testing

Tim Peters shows that the Dynamics people are probably right with their assertion regarding Cost Threshold for Parallelism:

These plans are from a SQL Server 2008 R2 SP3 instance that runs a version of Microsoft Dynamics. The MS Dynamics team knows their product issues a bunch of really small queries and recommend a Max Degree of Parallelism of 1. In my case there is one query plan with a cost of 34,402 query bucks that a MAXDOP = 1 can’t afford. Increasing the MAXDOP from 1 while keeping the Cost Threshold at 5 will keep all of my little queries running in their single threaded paradise while allowing some infrequent biguns to spread their lovely wings across a few more threads. My Cost Threshold For Parallelism is set to 5 and I hope to never have to defend my settings in a dark alley with Erik Darling.

Different systems will behave in different ways, so it makes sense that they might require different settings.  In the case of Dynamics, it appears that almost all of the queries are extremely low-cost, so relatively few plans would go parallel and the ones that do, you probably want going parallel.

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