FORCE_DISK causes the query engine to use disk rather than memory for temporary storage of the data required to process the JOIN operator. This frees up memory for other server operations. It is useful for queries that consume a large amount of memory and affect performance of other processes running on the server.

If FORCE_DISK is not specified, the query engine uses memory rather than disk, whenever possible, to maximize performance.

This option takes precedence over the SELECT-level FORCE_DISK option.