Select with grouping plan question - Mailing list pgsql-performance

This seems to me to be an expensive plan and I'm wondering if there's a
way to improve it or a better way to do what I'm trying to do here (get
a count of distinct values for each record_id and map that value to the
entity type) entity_type_id_mapping is 56 rows
volume_node_entity_data_values is approx 500,000,000 rows vq_record_id
has approx 11,000,000 different values vq_entity_type is a value in
entity_type_id_mapping.entity_type

I thought that the idx_vq_entities_1 index would allow an ordered scan
of the table. I created it based pon the sort key given in the explain
statement.

Thanks in advance.

                      Table "data_schema.volume_queue_entities"
     Column      |       Type        |                   Modifiers

-----------------+-------------------+----------------------------------
-----------------+-------------------+-------------
 vq_record_id    | bigint            | default
currval('seq_vq_fsmd_auto'::regclass)
 vq_entity_type  | character varying |
 vq_entity_value | character varying |
Indexes:
    "idx_vq_entities_1" btree (vq_record_id, vq_entity_type,
vq_entity_value)



                          Table "volume_8.entity_type_id_mapping"
   Column    |       Type        |                        Modifiers

-------------+-------------------+--------------------------------------
-------------+-------------------+--------------------
 entity_id   | integer           | default
nextval('volume_8.entity_id_sequence'::regclass)
 entity_type | character varying |



explain insert into volume_8.volume_node_entity_data_values
(vs_volume_id, vs_latest_node_synthetic_id, vs_base_entity_id, vs_value,
vs_value_count, vs_base_entity_revision_id)
     select 8, vq_record_id, entity_id , vq_entity_value,
count(vq_entity_value),1 from data_schema.volume_queue_entities qe,
volume_8.entity_type_id_mapping emap
    where qe.vq_entity_type = emap.entity_type group by
vq_record_id, vq_entity_type, vq_entity_value, entity_id ;


------------------------------------------------------------------------
----------------------------------------
 Subquery Scan "*SELECT*"  (cost=184879640.90..210689876.26
rows=543373376 width=60)
   ->  GroupAggregate  (cost=184879640.90..199822408.74 rows=543373376
width=37)
         ->  Sort  (cost=184879640.90..186238074.34 rows=543373376
width=37)
               Sort Key: qe.vq_record_id, qe.vq_entity_type,
qe.vq_entity_value, emap.entity_id
               ->  Hash Join  (cost=1.70..18234833.10 rows=543373376
width=37)
                     Hash Cond: (("outer".vq_entity_type)::text =
("inner".entity_type)::text)
                     ->  Seq Scan on volume_queue_entities qe
(cost=0.00..10084230.76 rows=543373376 width=33)
                     ->  Hash  (cost=1.56..1.56 rows=56 width=16)
                           ->  Seq Scan on entity_type_id_mapping emap
(cost=0.00..1.56 rows=56 width=16)
(9 rows)