Databases Reference
In-Depth Information
Finally, before we finish, don't forget to re-enable the
GbAggBeforeJoin
and
JNtoSM
transformation rules by running the following commands ...
DBCC
RULEON
(
'JNtoSM'
)
DBCC
RULEON
(
'GbAggBeforeJoin'
)
Listing 5-16.
... and verify that no transformation rules are still disabled, by running:
DBCC
SHOWOFFRULES
Listing 5-17.
You may also want to clear your plan cache to make sure none of these experiment plans
were left in memory, by once again running:
DBCC
FREEPROCCACHE
Listing 5-18.
The Memo
The memo structure was originally defined in
The Volcano Optimizer Generator
by Goetz
Graefe and William McKenna in 1993. As discussed in
Chapter 1, Introduction to Query
Optimization
, the SQL Server Query Optimizer is based on the Cascades Framework,
which was, in fact, a descendent of the Volcano optimizer.
The memo is a search data structure that is used to store the alternatives which are
generated and analyzed by the Query Optimizer. These alternatives can be logical or
