Controls how conservative the optimizer’s join result estimates are in unusually complex situations.
Option can be set at the database (PUBLIC) or user level. When set at the database level, the value becomes the default for any new user, but has no impact on existing users. When set at the user level, overrides the PUBLIC value for that user only. No system privilege is required to set option for self. System privilege is required to set at database level or at user level for any user other than self.
Requires the SET ANY PUBLIC OPTION system privilege to set this option. Can be set temporary for an individual connection or for the PUBLIC role. Takes effect immediately.
This option controls how conservative the join optimizer’s result size estimates are in situations where an input to a specific join has already passed through at least one intermediate join that can result in multiple copies of rows projected from the table being joined.
A level of zero indicates that the optimizer should use the same estimation method above intermediate expanding joins as it would if there were no intermediate expanding joins.
This results in the most aggressive (small) join result size estimates.
A level of 100 indicates that the optimizer should be much more conservative in its estimates whenever there are intermediate expanding joins, and this results in the most conservative (large) join result size estimates.
Normally, you should not need to change this value. If you do, set JOIN_EXPANSION_FACTOR as a temporary or user option.