The Story Of Nick

Kenneth Fisher tells the story of where the optimizer’s cost value comes from:

Obviously, it’s an important subject, right? And yet we keep seeing comments about how the cost is in seconds.

And to be fair, it is. It’s an estimate of how many seconds a query would take, if it was running on a developers workstation from back in the 90’s. At least that’s the story. In fact Dave Dustin (t) posted this interesting story today:

The best way to think of cost is as a probabilistic, ordinal, unitless value:  3 might be greater than 2; 1000 is almost certainly greater than 2; and “2 what?” is undefined.

Related Posts

Asynchronous Stats Updates

Monica Rathbun explains why you might want to turn on asynchronous statistics updates in your OLTP environment: By default, when Auto Update Statistics is set to True, the SQL Server Query Optimizer will automatically update statistics when data has met a threshold of changes (insert, update, delete, or merge) and the estimated rows are now […]

Read More

How Statistics In SQL Server Have Changed Over The Years

Erin Stellato gives us a version-based timeline of how SQL Server has handled statistics over the years: SQL Server 2008 Filtered statistics are introduced, and these can be created separately from a filtered index. There are some limitations around filtered indexes with regard to the Query Optimizer (see Tim Chapman’s post The Pains of Filtered Indexes and Paul […]

Read More

Categories

April 2017
MTWTFSS
« Mar May »
 12
3456789
10111213141516
17181920212223
24252627282930