Why is this simple SQL query so slow? - postgresql

Question

I have a query
select p.id
from Product p,Identifier i
where p.id=i.product_id
and p.aggregatorId='5109037'
and p.deletionDate is null
and i.type='03'
and i.value='9783639382891'
which takes about 3.5 seconds to run. Product has about 4.7m entries, Identifier about 20m. As you can see in the schema below, every column used in the query is indexed, but not all indexes are used. If I exclude the columns p.aggregatorId and i.type, the query runs as fast as I would have expected. I have also tried to join the Identifier table, but with no change in the explain plan.
Why the indexes are not used?
The explain plan looks like this:
Nested Loop (cost=3.21..63.48 rows=1 width=33) (actual time=10.856..3236.830 rows=1 loops=1)
-> Index Scan using idx_prod_aggr on product p (cost=0.43..2.45 rows=1 width=33) (actual time=0.041..191.339 rows=146692 loops=1)
Index Cond: ((aggregatorid)::text = '5109037'::text)
Filter: (deletiondate IS NULL)
-> Bitmap Heap Scan on identifier i (cost=2.78..61.01 rows=1 width=33) (actual time=0.019..0.019 rows=0 loops=146692)
Recheck Cond: ((product_id)::text = (p.id)::text)
Filter: (((type)::text = '03'::text) AND ((value)::text = '9783639382891'::text))
Rows Removed by Filter: 2"
-> Bitmap Index Scan on idx_id_prod_id (cost=0.00..2.78 rows=29 width=0) (actual time=0.016..0.016 rows=2 loops=146692)
Index Cond: ((product_id)::text = (p.id)::text)
The reduced DB schema looks like this:
CREATE TABLE product
(
id character varying(32) NOT NULL,
version integer,
active boolean,
aggregatorid character varying(15),
deletiondate timestamp without time zone,
)
WITH (
OIDS=FALSE
);
CREATE INDEX idx_prod_active
ON product
USING btree
(active);
CREATE INDEX idx_prod_aggr
ON product
USING btree
(aggregatorid COLLATE pg_catalog."default");
CREATE INDEX idx_prod_del_date
ON product
USING btree
(deletiondate);
CREATE TABLE identifier
(
id character varying(32) NOT NULL,
version integer,
typename character varying(50),
type character varying(3) NOT NULL,
value character varying(512) NOT NULL,
product_id character varying(32),
CONSTRAINT identifier_pkey PRIMARY KEY (id),
CONSTRAINT fk165a88c9c93f3e7f FOREIGN KEY (product_id)
REFERENCES product (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)
WITH (
OIDS=FALSE
);
CREATE INDEX idx_id_prod_type
ON identifier
USING btree
(type COLLATE pg_catalog."default");
CREATE INDEX idx_id_prod_value
ON identifier
USING btree
(value COLLATE pg_catalog."default");
CREATE INDEX idx_id_typename
ON identifier
USING btree
(typename COLLATE pg_catalog."default");
CREATE INDEX idx_prod_ident
ON identifier
USING btree
(product_id COLLATE pg_catalog."default");