By default, merge joins are enabled, at the server level, for allrows mix and for allrows_dss optgoal, and are disabled at the server level for other optgoals, including allrows_oltp. When merge joins are disabled, the server only costs other join types that are not disabled. To enable merge joins server-wide, set enable merge join to 1. The pre-version 15.0 configuration enable sort-merge joins and JTC does not affect the new query processor.
The command set merge_join on overrides the server level to allow use of merge joins in a session or stored procedure.
To enable merge joins, use:
set merge_join on
To disable merge joins, use:
set merge_join off
For information on configuring merge joins server-wide, see the System Administration Guide.
