SQL Server Execution Plans - Red Gate Software

OPTION ( FAST 10 );
Listing 5.16
Figure 5.12
Chapter 5: Controlling Execution Plans with Hints
Instead of the Merge Join operator for the join, the optimizer attempts to use a Nested
Loops operator. The loop join returns the first rows very fast, but the rest of the
processing was somewhat slower, which is perhaps to be expected, since the optimizer
focuses its efforts just on getting the first ten rows back as soon as possible.
The total estimated cost for the original query was 1.961. The hint reduced that cost to
0.012 (for the first 10 rows). The number of logical reads increases dramatically, from 1,238
for the un-hinted query to 101,827 for the hinted query. The actual speed of the execution
of the query increases only marginally, from around 4.6 seconds to 4.5 seconds. This slight
improvement is only going to get the first few rows back to the screen quickly. The overall
query won't run as fast once there is a load on the system and this query has to share disk
access with other queries, because of all those additional reads.
FORCE ORDER
Once again, our monitoring tools have identified a query that is performing poorly. It's
a long query with a number of tables being joined, as shown in Listing 5.17, which could
be somewhat concerning, because the more tables there are involved, the harder the
optimizer has to work.
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