postgresql - Postgres: speed up bitmap heap scan? -

i'm using postgres 9.3 , wondering if there way speed particular query on large table. these tables:

                                      table "public.frontend_prescription"       column       |          type           |                             modifiers -------------------+-------------------------+--------------------------------------------------------------------  id                | integer                 | not null default nextval('frontend_prescription_id_seq'::regclass)  presentation_code | character varying(15)   | not null  actual_cost       | double precision        | not null  processing_date   | date                    | not null  pct_id            | character varying(3)    | not null indexes:     "frontend_prescription_pkey" primary key, btree (id)     "frontend_prescription_4e2e609b" btree (pct_id)     "frontend_prescription_528f368c" btree (processing_date)     "frontend_prescription_b9b2c7ab" btree (presentation_code)     "frontend_prescription_cost_by_pres_code" btree (presentation_code, pct_id, actual_cost)     "frontend_prescription_presentation_code_69403ee04fda6522_like" btree (presentation_code varchar_pattern_ops)     "frontend_prescription_presentation_code_varchar_pattern_ops_idx" btree (presentation_code varchar_pattern_ops)             table "public.frontend_pct"       column       |          type           | modifiers -------------------+-------------------------+-----------  code              | character varying(3)    | not null  name              | character varying(200)  |  org_type          | character varying(9)    | not null 

and query spending ccg organisations month, on particular presentation_code:

select sum(frontend_prescription.actual_cost) val,         frontend_prescription.pct_id row_id,         frontend_prescription.processing_date date,         frontend_pct.name row_name  frontend_prescription, frontend_pct  (presentation_code='0407041t0bbacac')  , frontend_prescription.pct_id=frontend_pct.code  , frontend_pct.org_type='ccg'  group frontend_prescription.pct_id, frontend_pct.code, date  order date, row_id 

here results of explain (analyse, buffers) on query: http://explain.depesz.com/s/yrr5

it looks slow part bitmap heap scan on frontend_prescription. there way make faster? in particular, notice it's looping 211 times (once each pct found in data).

the table has many millions of rows, suspect there isn't, wanted check see if there obvious do.

-- tables (indexes omitted) create table frontend_pct (         code    varchar(3) not null primary key         , name  varchar(200)         , org_type      varchar(9)    not null         );  create table frontend_prescription (  id     serial not null primary key  , presentation_code varchar(15)        not null  , actual_cost  double precision not null  , processing_date      date not null  , pct_id       varchar(3) not null references frontend_pct(code)          );  -- rewritten query (shows flaws) explain analyze select        pr.pct_id row_id        , pr.processing_date zdate -- <<-- renamed this; "date" typename        , pc.name row_name         , sum(pr.actual_cost) val frontend_prescription pr join frontend_pct  pc on pr.pct_id=pc.code , pc.org_type='ccg' pr.presentation_code='0407041t0bbacac' group pr.pct_id, pc.code, zdate         -- ^^ ------ ^^ <- these same (maybe meant pc.name ??)                         -- (which functionally dependent on pc.code) order zdate, row_id  -- <-- strange order; why not same "group by"         ;