set max_parallel_workers_per_gather=4;
set force_parallel_mode=on;
set parallel_setup_cost = 10;
set parallel_tuple_cost = 0.001;
create table parallel_test(i int, b1 base62, b2 bigbase62, b3 hugebase62) with (parallel_workers = 4);
insert into parallel_test (i, b1, b2, b3)
select i, i::int, i::bigint, i::text::hugebase62
from generate_series(1,1e4) i;
explain (costs off,verbose)
select count(*) from parallel_test where b1 = '1ftese';
                            QUERY PLAN                             
-------------------------------------------------------------------
 Finalize Aggregate
   Output: count(*)
   ->  Gather
         Output: (PARTIAL count(*))
         Workers Planned: 4
         ->  Partial Aggregate
               Output: PARTIAL count(*)
               ->  Parallel Seq Scan on public.parallel_test
                     Output: i, b1, b2, b3
                     Filter: (parallel_test.b1 = '1ftese'::base62)
(10 rows)

explain (costs off,verbose)
select count(*) from parallel_test where b2 = '1ftese';
                              QUERY PLAN                              
----------------------------------------------------------------------
 Finalize Aggregate
   Output: count(*)
   ->  Gather
         Output: (PARTIAL count(*))
         Workers Planned: 4
         ->  Partial Aggregate
               Output: PARTIAL count(*)
               ->  Parallel Seq Scan on public.parallel_test
                     Output: i, b1, b2, b3
                     Filter: (parallel_test.b2 = '1ftese'::bigbase62)
(10 rows)

explain (costs off,verbose)
select count(*) from parallel_test where b3 = '100000';
                              QUERY PLAN                               
-----------------------------------------------------------------------
 Finalize Aggregate
   Output: count(*)
   ->  Gather
         Output: (PARTIAL count(*))
         Workers Planned: 4
         ->  Partial Aggregate
               Output: PARTIAL count(*)
               ->  Parallel Seq Scan on public.parallel_test
                     Output: i, b1, b2, b3
                     Filter: (parallel_test.b3 = '100000'::hugebase62)
(10 rows)

explain (costs off,verbose)
select b1, count(*) from parallel_test group by 1;
                         QUERY PLAN                          
-------------------------------------------------------------
 Finalize HashAggregate
   Output: b1, count(*)
   Group Key: parallel_test.b1
   ->  Gather
         Output: b1, (PARTIAL count(*))
         Workers Planned: 4
         ->  Partial HashAggregate
               Output: b1, PARTIAL count(*)
               Group Key: parallel_test.b1
               ->  Parallel Seq Scan on public.parallel_test
                     Output: i, b1, b2, b3
(11 rows)