set effective_io_concurrency=0; set enable_indexscan=off; set enable_seqscan=off; explain (analyze, buffers)  select * from test where id between 0 and 100000 and val != '';
                                                         QUERY PLAN                                                          
-----------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on test  (cost=7.62..467.66 rows=498 width=36) (actual time=210.949..518.513 rows=100000 loops=1)
   Recheck Cond: ((id >= 0) AND (id <= 100000))
   Filter: (val <> ''::text)
   Heap Blocks: exact=1539
   Buffers: shared read=1814
   ->  Bitmap Index Scan on test_pkey  (cost=0.00..7.49 rows=500 width=0) (actual time=209.172..209.172 rows=100000 loops=1)
         Index Cond: ((id >= 0) AND (id <= 100000))
         Buffers: shared read=275
 Planning time: 68.902 ms
 Execution time: 524.671 ms
(10 rows)

set effective_io_concurrency=1; set enable_indexscan=off; set enable_seqscan=off; explain (analyze, buffers)  select * from test where id between 0 and 100000 and val != '';
                                                        QUERY PLAN                                                         
---------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on test  (cost=7.62..467.66 rows=498 width=36) (actual time=77.710..413.798 rows=100000 loops=1)
   Recheck Cond: ((id >= 0) AND (id <= 100000))
   Filter: (val <> ''::text)
   Heap Blocks: exact=1539
   Buffers: shared read=1814
   ->  Bitmap Index Scan on test_pkey  (cost=0.00..7.49 rows=500 width=0) (actual time=76.590..76.590 rows=100000 loops=1)
         Index Cond: ((id >= 0) AND (id <= 100000))
         Buffers: shared read=275
 Planning time: 921.318 ms
 Execution time: 420.000 ms
(10 rows)

set effective_io_concurrency=0; set enable_indexscan=off; set enable_seqscan=off; explain (analyze, buffers)  select * from test where id between 0 and 100000 and val != '';
                                                        QUERY PLAN                                                         
---------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on test  (cost=7.62..467.66 rows=498 width=36) (actual time=64.313..435.762 rows=100000 loops=1)
   Recheck Cond: ((id >= 0) AND (id <= 100000))
   Filter: (val <> ''::text)
   Heap Blocks: exact=1539
   Buffers: shared read=1814
   ->  Bitmap Index Scan on test_pkey  (cost=0.00..7.49 rows=500 width=0) (actual time=60.630..60.630 rows=100000 loops=1)
         Index Cond: ((id >= 0) AND (id <= 100000))
         Buffers: shared read=275
 Planning time: 87.523 ms
 Execution time: 441.813 ms
(10 rows)

set effective_io_concurrency=1; set enable_indexscan=off; set enable_seqscan=off; explain (analyze, buffers)  select * from test where id between 0 and 100000 and val != '';
                                                        QUERY PLAN                                                         
---------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on test  (cost=7.62..467.66 rows=498 width=36) (actual time=97.773..492.354 rows=100000 loops=1)
   Recheck Cond: ((id >= 0) AND (id <= 100000))
   Filter: (val <> ''::text)
   Heap Blocks: exact=1539
   Buffers: shared read=1814
   ->  Bitmap Index Scan on test_pkey  (cost=0.00..7.49 rows=500 width=0) (actual time=96.454..96.454 rows=100000 loops=1)
         Index Cond: ((id >= 0) AND (id <= 100000))
         Buffers: shared read=275
 Planning time: 56.608 ms
 Execution time: 498.591 ms
(10 rows)

set effective_io_concurrency=0; set enable_indexscan=off; set enable_seqscan=off; explain (analyze, buffers)  select * from test where id between 0 and 100000 and val != '';
                                                        QUERY PLAN                                                         
---------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on test  (cost=7.62..467.66 rows=498 width=36) (actual time=71.043..656.677 rows=100000 loops=1)
   Recheck Cond: ((id >= 0) AND (id <= 100000))
   Filter: (val <> ''::text)
   Heap Blocks: exact=1539
   Buffers: shared read=1814
   ->  Bitmap Index Scan on test_pkey  (cost=0.00..7.49 rows=500 width=0) (actual time=57.814..57.814 rows=100000 loops=1)
         Index Cond: ((id >= 0) AND (id <= 100000))
         Buffers: shared read=275
 Planning time: 77.376 ms
 Execution time: 662.838 ms
(10 rows)

set effective_io_concurrency=1; set enable_indexscan=off; set enable_seqscan=off; explain (analyze, buffers)  select * from test where id between 0 and 100000 and val != '';
                                                        QUERY PLAN                                                         
---------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on test  (cost=7.62..467.66 rows=498 width=36) (actual time=57.230..425.477 rows=100000 loops=1)
   Recheck Cond: ((id >= 0) AND (id <= 100000))
   Filter: (val <> ''::text)
   Heap Blocks: exact=1539
   Buffers: shared read=1814
   ->  Bitmap Index Scan on test_pkey  (cost=0.00..7.49 rows=500 width=0) (actual time=55.374..55.374 rows=100000 loops=1)
         Index Cond: ((id >= 0) AND (id <= 100000))
         Buffers: shared read=275
 Planning time: 64.964 ms
 Execution time: 431.503 ms
(10 rows)

