gistfile1.txt

create table tst_complex_index (
	id1 int not null,
	id2 int not null,
	value text,
	primary key (id1, id2)
);

insert into tst_complex_index (id1, id2, value)
select (9*g.i + 177) % 100, (191*g.i + 197) % 10001, g.i || ' text ' || (g.i + 7) % 19
from generate_series(1, 1000*1000) g (i);

explain (analyze,buffers)
select * from tst_complex_index
where id2 = 1 ;

QUERY PLAN                                                                                                                                        |
--------------------------------------------------------------------------------------------------------------------------------------------------+
Index Scan using tst_complex_index_pkey on tst_complex_index  (cost=0.42..11637.42 rows=100 width=22) (actual time=0.015..17.965 rows=100 loops=1)|
  Index Cond: (id2 = 1)                                                                                                                           |
  Buffers: shared hit=3746                                                                                                                        |
Planning Time: 0.040 ms                                                                                                                           |
Execution Time: 18.018 ms                                                                                                                         |