Context Switches In SQL Server

Ewald Cress continues his journey to the center of the SQLOS:

The SQLOS scheduler exists in the cracks between user tasks. As we’re well aware, in order for scheduling to happen at all, it is necessary for tasks to run scheduler-friendly code every now and again. In practice this means either calling methods which have the side effect of checking your quantum mileage and yielding if needed, or explicitly yielding yourself when the guilt gets too much.

Now from the viewpoint of the user task, the experience of yielding is no different than the experience of calling any long-running CPU-intensive function: You call a function and it eventually returns. The real difference is that the CPU burned between the call and its return was spent on one or more other threads, while the current thread went lifeless for a bit. But you don’t know that, because you were asleep at the time!

Definitely read the whole thing.

Related Posts

Unboxing ISPACs

It’s an early Christmas for Richie Lee: The first file that we’re going to look at is the [Content_Types].xml file, and this is the file that confirms that the ZipPackage class is used. There’s an article here that is ten years old but is still valid (scroll down to the System.IO.Packaging INcludes Zip Support to read up on this.) […]

Read More

Diving Into Spark’s Cost-Based Optimizer

Ron Hu, et al, explain how Spark’s cost-based optimizer works: At its core, Spark’s Catalyst optimizer is a general library for representing query plans as trees and sequentially applying a number of optimization rules to manipulate them. A majority of these optimization rules are based on heuristics, i.e., they only account for a query’s structure and ignore […]

Read More

Categories

August 2017
MTWTFSS
« Jul Sep »
 123456
78910111213
14151617181920
21222324252627
28293031