Asynchronous processing of federated queries

Asynchrony is a method of improving query performance by running multiple parts of an access plan concurrently to reduce the elapsed time for a given query.

In a federated system, data is distributed across systems at multiple data sources, and each system has its own resources. Asynchrony overlaps the operations that use those resources so that multiple systems remain active at the same time. Overlapping operations enables multiple parts of an access plan to run concurrently rather than serially.

Complex queries that involve time-consuming operations on remote data sources can benefit from asynchrony. Asynchrony enables the following types of operations to take place concurrently:

Two or more operations on remote data sources
Operations on the federated server and at least one remote data source

As query operations consume resources, asynchrony can benefit systems in which resources are idle or when only one of the data sources, or the federated system, is doing work at any point in time.