Multistep parallelism is the simultaneous performance of multiple steps across all units of parallelism in the system.
Teradata Database is the only commercially available relational database management system to implement multistep parallelism. Whenever possible, the Teradata Database invokes one or more processes for each step in a request to perform an operation. Multiple steps for the same request execute simultaneously as long as they are not dependent of the results of previous steps.
You can recognize multistep parallelism in EXPLAIN reports by the dot notation used for the parallel steps; multistep parallelism is illustrated in the following graphic:
This diagram shows the steps the Optimizer might generate for a 4-AMP system configuration. Note the multistep parallelism with steps 1 and 2, where steps 1.1 and 1.2 run in parallel with one another as do steps 2.1 and 2.2, respectively.