Gained %20 performance after disabling bitmapscan

Hi all,

I have a problem with my query. Query always using parallel bitmap heap scan. I've created an index with all where conditions and id but query does not this index and continue to use bitmapscan. So I decided disable bitmap scan for testing. And after that, things became strange. Cost is higher, execution time is lower.
But I want to use index_only_scan because index have all column that query need. No need to access table.

It is doing index_only_scan when disabling bitmap scan but I cannot disable bitmap scan for cluster wide. There are other queries...
Can you help me to solve the issue?

PostgreSQL Version: PostgreSQL 10.3 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16), 64-bit

Here my query:

explain analyze with ids as (

select g.id,g.kdv,g.tutar from 

dbs.gider g

left join dbs.gider_belge gb

on gb.id=g.gider_belge_id

where gb.mukellef_id='0123456789' and g.deleted is not true and gb.deleted is not true and gb.sube_no='-13' and gb.defter='sm' and gb.kayit_tarihi>='2018-01-01 00:00:00'),

totals as (select sum(kdv) tkdv,sum(tutar) ttutar from ids)

select ids.id,totals.tkdv,totals.ttutar from ids,totals;

Here default explain analyze output:

Nested Loop  (cost=25939.84..26244.15 rows=10143 width=72) (actual time=92.936..94.708 rows=12768 loops=1)

   CTE ids

     ->  Gather  (cost=1317.56..25686.25 rows=10143 width=20) (actual time=12.774..87.854 rows=12768 loops=1)

           Workers Planned: 2

           Workers Launched: 2

           ->  Nested Loop  (cost=317.56..23671.95 rows=4226 width=20) (actual time=5.382..80.240 rows=4256 loops=3)

                 ->  Parallel Bitmap Heap Scan on gider_belge gb  (cost=316.99..10366.28 rows=3835 width=8) (actual time=5.223..29.208 rows=4077 loops=3)

                       Recheck Cond: (((mukellef_id)::text = '0123456789'::text) AND (kayit_tarihi >= '2018-01-01 00:00:00'::timestamp without time zone) AND (sube_no = '-13'::integer) AND ((defter)::text

 = 'sm'::text) AND (deleted IS NOT TRUE))

                       Heap Blocks: exact=7053

                       ->  Bitmap Index Scan on idx_gider_belge_mukellef_id_kayit_tarihi_sube_no_defter_id  (cost=0.00..314.69 rows=9205 width=0) (actual time=8.086..8.086 rows=12230 loops=1)

                             Index Cond: (((mukellef_id)::text = '0123456789'::text) AND (kayit_tarihi >= '2018-01-01 00:00:00'::timestamp without time zone) AND (sube_no = '-13'::integer) AND ((defter)::

text = 'sm'::text))

                 ->  Index Scan using idx_gider_gider_belge_id on gider g  (cost=0.56..3.41 rows=6 width=28) (actual time=0.012..0.012 rows=1 loops=12230)

                       Index Cond: (gider_belge_id = gb.id)

                       Filter: (deleted IS NOT TRUE)

                       Rows Removed by Filter: 0

   CTE totals

     ->  Aggregate  (cost=253.58..253.59 rows=1 width=64) (actual time=92.925..92.925 rows=1 loops=1)

           ->  CTE Scan on ids ids_1  (cost=0.00..202.86 rows=10143 width=40) (actual time=12.776..90.976 rows=12768 loops=1)

   ->  CTE Scan on totals  (cost=0.00..0.02 rows=1 width=64) (actual time=92.926..92.927 rows=1 loops=1)

   ->  CTE Scan on ids  (cost=0.00..202.86 rows=10143 width=8) (actual time=0.001..0.820 rows=12768 loops=1)

 Planning time: 0.691 ms

 Execution time: 113.107 ms

Here explain analyze output after disabling bitmapscan:

Here my index:

dbs=# \d dbs.idx_gider_belge_mukellef_id_kayit_tarihi_sube_no_defter_id 

Index "dbs.idx_gider_belge_mukellef_id_kayit_tarihi_sube_no_defter_id"

    Column    |            Type             |  Definition  

--------------+-----------------------------+--------------

 mukellef_id  | character varying(12)       | mukellef_id

 kayit_tarihi | timestamp without time zone | kayit_tarihi

 sube_no      | integer                     | sube_no

 defter       | character varying(4)        | defter

 id           | bigint                      | id

btree, for table "dbs.gider_belge", predicate (deleted IS NOT TRUE)

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