Access plans optimized for asynchrony

In an asynchronous operation, a table queue (TQ) operator is inserted directly above the SHIP or RPD operator in the execution plan. The TQ operator defines a portion of the plan, called a subplan. A separate process or thread, with its own memory, runs the subplan. A subplan initiates immediately when the query starts.

You can think of the TQ operator as a pipe between the SHIP or RPD operator (producer of data) and the operator above it (consumer of data) in the plan. This pipe decouples the execution of the SHIP in the subplan below it from the main plan, and allows the asynchronous exchange of data between the two plan sections.

A TQ operator that appears directly above a SHIP or RPD operator in the plan enables the remote operations that the SHIP or RPD operator define to initiate at the beginning of the query and to deliver results to the federated server asynchronously. When asynchrony is beneficial for a given remote operation, the optimizer places a TQ operator directly above the corresponding SHIP or RPD operator in the plan.

TQ operators occur in execution plans for different purposes. A TQ operator usually denotes parallel operations in partitioned databases or in databases enabled for intrapartition parallelism. Another type of TQ operator, that enables asynchronous execution of a subplan, is called an asynchrony TQ (ATQ).