rechte=> explain (analyze, buffers) SELECT count(*)
       FROM  t_demo
       WHERE id_sorted BETWEEN 10000 AND 20000
mrechte-> ;
                                                             QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=348.77..348.78 rows=1 width=8) (actual time=0.934..0.935 rows=1 loops=1)
   Buffers: shared hit=6 read=28
   ->  Index Only Scan using idx_id on t_demo  (cost=0.43..322.95 rows=10326 width=0) (actual time=0.017..0.640 rows=10001 loops=1)
         Index Cond: ((id_sorted >= 10000) AND (id_sorted <= 20000))
         Heap Fetches: 0
         Buffers: shared hit=6 read=28
 Planning:
   Buffers: shared hit=37 read=4
 Planning Time: 0.131 ms
 Execution Time: 0.948 ms
(10 lignes)

mrechte=> explain (analyze, buffers) SELECT count(*)
       FROM  t_demo
       WHERE id_random BETWEEN 10000 AND 10000000;
                                                               QUERY PLAN

------------------------------------------------------------------------------------------------------------------------------------
----
 Aggregate  (cost=408.98..408.99 rows=1 width=8) (actual time=1.137..1.137 rows=1 loops=1)
   Buffers: shared hit=36
   ->  Index Only Scan using idx_random on t_demo  (cost=0.43..378.69 rows=12113 width=0) (actual time=0.020..0.760 rows=11699 loops
=1)
         Index Cond: ((id_random >= 10000) AND (id_random <= 10000000))
         Heap Fetches: 0
         Buffers: shared hit=36
 Planning Time: 0.061 ms
 Execution Time: 1.154 ms
(8 lignes)