TOP 1 Tuning

Kenneth Fisher has a good case study on tuning with the help of Rob Farley:

Here we are looking at the difference between the estimated and actual number of rows for an element of the plan. To look at this information you can either mouse over the element or right click and open the properties tab. In this case you will see that the estimated number of rows (what the optimizer thought would happen) is fairly low (117) particularly compared to what actually happened (1494900). When you see a big difference like that in a query plan there is something wrong.

This is a really nice and detailed walkthrough in which Rob plays Socrates and Kenneth your favorite of the group (Thrasymachus anyone?).

Related Posts

Creating Temp Staging Tables to Avoid Spooling

Bert Wagner shows how you can create your own tables in tempdb to avoid eager or lazy spools: SQL Server Spool operators are a mixed bag. On one hand, they can negatively impact performance when writing data to disk in tempdb. On the other hand, they allow filtered and transformed result sets to be temporarily […]

Read More

Rewriting Expensive Updates

Erik Darling takes us through an experiment: Let’s also say that bad query is taking part in a modification. UPDATE u2SET u2.Reputation *= 2FROM Users AS uJOIN dbo.Users AS u2ON CHARINDEX(u.DisplayName, u2.DisplayName) > 0WHERE u2.Reputation >= 100000;AND u.Id <> u2.Id; This query will run for so long that we’ll get sick of waiting for it. […]

Read More

Categories

March 2016
MTWTFSS
« Feb Apr »
 123456
78910111213
14151617181920
21222324252627
28293031