SQL Server Execution Plans - Red Gate Software

FAST n
Chapter 5: Controlling Execution Plans with Hints
Let's assume that we are not concerned about the performance of the database. This time,
we're concerned about perceived performance of the application. The users would like an
immediate return of data to the screen, even if it's not the complete result set, and even
if they have to wait longer for the complete result set. This could be a handy way to get
a little bit of information in front of people quickly, so that they can decide whether it's
important and either move on or wait for the rest of the data.
The FAST n hint provides this ability by getting the optimizer to focus on getting the
execution plan to return the first "n" rows as fast as possible, where "n" is a positive
integer value. Consider the following query and execution plan.
SELECT *
FROM Sales.SalesOrderDetail sod
JOIN Sales.SalesOrderHeader soh
ON sod.SalesOrderID = soh.SalesOrderID;
Listing 5.15
Figure 5.11
This query performs adequately considering the fact that it's selecting all the data from
the tables without any sort of filtering operation, but there is a delay before the end-users
see any results, so we can try to fix this by adding the FAST N hint to return the first 10
rows as quickly as possible.
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