Reading Execution plans

One of the more common questions I get from colleagues is on how to read the execution plan that SQL produces. At first I found it quite a hard question to answer as no one really taught me how to read them. When I started with performance tuning I got a bit thrown in the deep end.

This is going to be the first in a series, maybe short, maybe long, on reading SQL’s execution plans. I’m going to go into the overall structure of a plan; the differences between the actual and the estimated plans, and how to obtain both; and some of the more common query operators and how they affect query performance.

If you have any specific questions that you’d like answering regarding execution plans, please post a comment here. Otherwise I’m going to ramble on a bit touching on things that I feel are important and relevant and maybe missing things that you would like to know.

Current articles in this series, in order of writing, are

1. Structure of an execution plan
2. Execution plans, estimated vs actual
3. Execution plans from Profiler
4. A basic execution plan
5. Execution plan operations – scans and seeks
6. Execution plan operations – joins
7. Execution plan operations – aggregate
8. Execution plan operations – misc
9. Execution plans – important properties
10. Execution plan – more properties
11. An example execution plan

There is more to come.