SOS_SCHEDULER_YIELD And Hypervisors

Jonathan Kehayias has an interesting article on generating SOS_SCHEDULER_YIELD waits due to CPU over-subscription on the host:

The test environment that I used for this is a portable lab I’ve used for demos for VM content over the last eight years teaching our Immersion Events. The ESX host has 4 cores and 8GB RAM and hosts three virtual machines, a 4vCPU SQL Server with 4GB RAM, and two 2vCPU Windows Server VM’s with 2GB RAM that are used strictly to run Geekbench to produce load.  Within SQL Server, I a reproducible workload that drives parallelism and is repeatable consistently, that I have also used for years in teaching classes.
For the tests, I first ran a baseline where the SQL Server VM is the only machine executing any tasks/workload at all, but the other VMs are powered on and just sitting there on the hose.  This establishes a base metric in the host and had 1% RDY time average during the workload execution, after which I collected the wait stats for SOS_SCHEDULER_YIELD.

From there, Jonathan starts cranking up the load on the application servers and sees what it does to SQL Server ready time. This is a great reason not to over-subscribe on CPUs on mission-critical hosts.

Related Posts

Thoughts on Certification

Eugene Meidinger is certifiable: This being a complex topic, I thought I’d lay out the various factors to give a more comprehensive answer than you can easily fit in a tweet. So the first two questions we need to answer are “Why do certs exist?” and “Why do people take them?”. Without these, we can’t […]

Read More

Disable Lightweight Pooling

Randolph West explains why enabling lightweight pooling in SQL Server is almost always a bad idea: When can I enable lightweight pooling then?Don’t. But if you must, these are the conditions under which Microsoft suggests it may be useful:– Large multi-processor servers are in use.– All servers are running at or near maximum capacity.– A lot […]

Read More

Categories

January 2019
MTWTFSS
« Dec Feb »
 123456
78910111213
14151617181920
21222324252627
28293031