MAXSCAN Environment Option (XPS)

Use the MAXSCAN environment option to change the default number of scan threads on each coserver. The default is three scan threads for each CPU VP. You might want to reduce the number of scan threads on a coserver if the GROUP, JOIN, and other operators above the scan are not producing rows quickly enough to keep the default number of scan threads busy.

For some queries, you might want to increase the number of scan threads on each coserver. For example, if each coserver has three CPU VPs, the database server can create nine scan threads on each coserver. To increase the number to four threads for each CPU VP, execute the following statement:

SET ENVIRONMENT MAXSCAN '12'

MAXSCAN is automatically set to 1 if the COMPUTE_QUOTA environment option is enabled or if the isolation level is set to Cursor Stability and the database server can use a pipe operator.