Changes to the TASM AMP Worker Task Event in Teradata 13.10 - comment by carrie

Lakshimi,
 
You are correct that parallel steps can result in more than 1 or 2 AMP worker tasks being used by a single request, particularly if it is multistatement request.    But even with multiple parallel steps in the plan, most requests will be limited to 4 AWTs at the same time. 
 
This is because of limitations related to other internal structures (called channels) that manage cross-AMP communication within a request.   Things like step completion coordination or abort coordination are performed by channels behind the scenes.  So you could have a plan with 8 parallel steps in the plan, but at run-time they will not all execute at the same time.   If the first 4 steps only use a single AWT each, then all 4 could run at the same time.  But if the first two required 2 AWTs at the same time, then only the first two would actually run at the same time. 
 
Even if you hade two parallel steps and each was doing row redistribution and so required 2 AWTs each, and you had 4 AWTs active at a time, there is usually one of the two parallel steps that is longer running while the other is usually much shorter, so the actual time that 4 AWTs are held by the request might be shorter than you would expect.  However,  If there are other parallel steps to be run in that high-level step, they will run, as long as the combination of sub-steps doesn't require more than 4 AWTs.
 
Thanks, -Carrie