I also feel difficult to distinguish the aggregator and non-aggregator in the ad_read_coll.c,

for example, in function ADIOI_R_Exchange_data,

how can I know it is executed by a process or an aggregator?

I can only see how 'nprocs_for_coll' is used in partitioning the file domain,

but couldn't see how it is used to tell the certain number of aggregator to do the collective I/O.