Planning to Increase Cost Threshold for Parallelism – Like a Smart Person!

When administrating a SQL Server instance with multiple CPU cores and heavy workload, it’s common to see SQL Server creating and using execution plans with parallelism. The instance configuration “cost threshold for parallelism” is what determines for SQL Server the minimum sub-tree cost before it starts considering to create a parallelism plan. The default “out-of-the-box” value of this configuration is 5.

 However, in some cases, we would want to increase the default configuration of “cost threshold for parallelism” to something higher than the Microsoft default of 5, thus decreasing the frequency in which SQL Server creates parallelism plans.

This is something we would usually want to do when we see too much CPU workload as a result of parallelism plans, and we would want to reduce it. 

But how can we know which new value we should use? Do we just throw a randomly high number such as 50 and see what happens (as is often recommended in most blogs)?

Well, no, we don’t actually have to do that.

We can do it like smart people.

Being smart is a good thing.… Read More Planning to Increase Cost Threshold for Parallelism – Like a Smart Person!

The LOOP, HASH and MERGE Join Types

Today I’ll talk about the available JOIN operator types in SQL Server (Nested Loops, Hash and Merge Joins), their differences, best practices and complexity. For the samples in this post, we’ll use the free AdventureWorks database sample available here: http://msftdbprodsamples.codeplex.com/releases/view/4004 Introduction: What are Join Operators? A join operator is a type of an algorithm which… Read More The LOOP, HASH and MERGE Join Types

The "IGNORE_DUP_KEY" option in Primary Keys and Unique Indexes

Unlike foreign keys, primary keys and unique indexes cannot be “untrusted”. There’s no “NOCHECK” option for unique constraints. The closest there is, is the “ignore_dup_key” option. “Hmm… That sounds interesting”, you must be thinking. But let me stop you right there, buddy. Read this before you go off doing something potentially dangerous… Very, VERY dangerous.… Read More The "IGNORE_DUP_KEY" option in Primary Keys and Unique Indexes

The Curious Case of Collations and Performance in SQL Server

One fateful night, cold and dreary, I’ve stumbled upon an apparently little known fact about SQL Server – specifically SQL Server collations and how they affect performance… Yes, really!

While normalizing a table in their database, one of my clients had weird and inconsistent performance problems and couldn’t find a solution for it for quite a while.… Read More The Curious Case of Collations and Performance in SQL Server