activity_id and operator_id in profile table

qihua_wu

After ran a complex query profile, we save it to adhoc.profile_backup. Using the following query, we found one operation_id can be used by multiple activiity_id. operation_id is the number of a thread, then what's activity id?

And why a single sort has 4 activity id?

select distinct activity_id, operator_id from adhoc.profile_backup where path_id=62 and operator_name ilike 'sort' and node_name='v_node0032' and counter_value>0 order by operator_id