11.5. Multi-Source Models: Planning and Execution

The planner logically treats a multi-source table as if it were a view containing the union all of the respective source tables. More complex partitioning scenarios, such as heterogeneous sources or list partitioning will require the use of a Partitioned Union.

Most of the federated optimizations available over unions are still applicable in multi-source mode. This includes aggregation pushdown/decomposition, limit pushdown, join partitioning, etc.