User's Manual

61
Building Streams
Figure 5-19
Setting stream optimization options
Note: W
hether SQ L pushback an d optimization ar e supported depends on the type of database in
use. For the late st information on which databases and ODBC drivers are supported and tested for
use with IBM® SP SS® Modeler 15, see the corpo r ate Suppor t site at http://www.ibm.com/support.
Enable stream rewriting. Select this option to enable stream rew r iting in SPSS Modeler. Two types
of rewriting a r e available, and you can select one or both. Stream rewriting reorders the nod es in a
stream behind the scenes for more efficient operation, without altering stream semantics.
 Optimize SQL generation. This option enables nodes to be reordered within the stream s o that
more operations c an be pushed back using SQL generation for execution in the database.
When it finds a node th at ca nnot be rendered into SQL, the optimizer will look ahead to
see if there are any downstream nodes that can be rendered into SQL and safely moved in
fron
t of the problem node witho ut affecting the stream semantics. Not only can the database
perform operations more efficiently than SPSS Modeler, but such pushbacks act to reduce
the size of the data set that is returned to SPSS Modeler for processin g. This, in tur n, can