Parallelism Showplan Operator
The Parallelism operator performs the distribute streams, gather streams, and repartition streams logical operations. The Argument columns can contain a PARTITION COLUMNS:() predicate with a comma-separated list of the columns being partitioned. The Argument columns can also contain an ORDER BY:() predicate, listing the columns to preserve the sort order for during partitioning.
Parallelism is a physical operator.
If a query has been compiled as a parallel query, but at run time it is run as a serial query, the Showplan output generated by SET STATISTICS XML or by using the Include Actual Execution Plan option in SQL Server Management Studio will not contain the RunTimeInformation element for the Parallelism operator. In SET STATISTICS PROFILE output, the actual row counts and actual number of executes will display zeroes for the Parallelism operator. When either condition occurs, it means that the Parallelism operator was only used during query compilation and not in the run-time query plan. Note that sometimes parallel query plans are run in serial if there is a high concurrent load on the server.