drop table if exists foo;
create table foo (x daterange, i int, t text);
insert into foo select daterange(x::date,x::date+3), random()*3000 from (select now()-interval '3 years'*random() as x from generate_series(1,1e6))foo;
vacuum analyze foo;
create index ON  foo using gist  ( x);
create index ON  foo   ( i);
explain (analyze, buffers) select * from generate_series(1,20) g(i), foo where x && '[2019-08-09,2019-08-11)' and g.i=foo.i;
\q
                                                              QUERY PLAN                                                               
---------------------------------------------------------------------------------------------------------------------------------------
 Nested Loop  (cost=170.21..3563.24 rows=33 width=54) (actual time=1.295..24.890 rows=28 loops=1)
   Buffers: shared hit=543 read=8
   I/O Timings: read=0.040
   ->  Function Scan on generate_series g  (cost=0.00..0.20 rows=20 width=4) (actual time=0.007..0.014 rows=20 loops=1)
   ->  Bitmap Heap Scan on foo  (cost=170.21..178.13 rows=2 width=50) (actual time=1.238..1.240 rows=1 loops=20)
         Recheck Cond: ((i = g.i) AND (x && '[2019-08-09,2019-08-11)'::daterange))
         Heap Blocks: exact=28
         Buffers: shared hit=543 read=8
         I/O Timings: read=0.040
         ->  BitmapAnd  (cost=170.21..170.21 rows=2 width=0) (actual time=1.234..1.234 rows=0 loops=20)
               Buffers: shared hit=515 read=8
               I/O Timings: read=0.040
               ->  Bitmap Index Scan on foo_i_idx  (cost=0.00..6.92 rows=333 width=0) (actual time=0.031..0.031 rows=327 loops=20)
                     Index Cond: (i = g.i)
                     Buffers: shared hit=55 read=8
                     I/O Timings: read=0.040
               ->  Bitmap Index Scan on foo_x_idx  (cost=0.00..161.78 rows=5000 width=0) (actual time=1.183..1.183 rows=3670 loops=20)
                     Index Cond: (x && '[2019-08-09,2019-08-11)'::daterange)
                     Buffers: shared hit=460
 Planning:
   Buffers: shared hit=47 read=4
   I/O Timings: read=0.034
 Planning Time: 0.380 ms
 Execution Time: 24.937 ms
(24 rows)

Time: 26.094 ms