I am not sure about that. The string it not-unique because it does not contain the result_grp_ordinal, so multiple tasks have the same string and can be grouped together. This is how I look at the times:

  [[code]]
   select operation, sum(duration) as duration, max(pymemory) as pymemory, 
   max(pgmemory) as pgmemory, count(*) from uiapi.performance 
   where oq_job_id=(select max(id) from uiapi.oq_job)
   group by operation order by duration desc;
 [[code]]