[HACKERS] Doubt in index subplan query

Hello, I have a query plan for a certain query  Nested Loop  (cost=100000000.00..38761761090.50 rows=3000608 width=8)    ->  Seq Scan on lineitem  (cost=100000000.00..100213649.15 rows=6001215 width=8)    ->  Index Scan using oindex2 on myorders  (cost=0.00..6442.27 rows=1 width=4)          Index Cond: ("outer".l_orderkey = myorders.o_orderkey)          Filter: (subplan)          SubPlan            ->  Index Scan using cnation on customer  (cost=0.00..12859.39 rows=5251 width=0)                  Index Cond: (c_nationkey = 10) How is the subplan handled by postgres at index level ? Is any sort of hashing done ? Thanks and regards, Suresh