query cost too high, anyway to reduce it - Mailing list pgsql-performance

----------------------------------------------
TABLE STRUCTURE
----------------------------------------------

CREATE TABLE gbobjects
(
  ssid bigint NOT NULL,
  nid character varying NOT NULL,
  inid bigint NOT NULL,
  uid bigint NOT NULL,
  status character varying,
  noofchanges integer NOT NULL,
  fieldschanged character varying[] NOT NULL,
  changetype bigint[] NOT NULL,
  noofcommits integer NOT NULL,
  noofchangesaftercommit integer NOT NULL,
  history bigint[] NOT NULL,
  gbtimestamp timestamp with time zone DEFAULT now(),
  rendered_nbh text,
  nbh text,
  CONSTRAINT gbobjects_pkey PRIMARY KEY (ssid)
)
WITH (OIDS=FALSE);
ALTER TABLE gbobjects OWNER TO postgres;


-- Index: nid_object

CREATE INDEX nid_object
  ON gbobjects
  USING btree
  (nid);


-------------------------------------------------------
using EXPLAIN
-------------------------------------------------------

We populated the table with data and used EXPLAIN


dbpedia=# EXPLAIN   SELECT   nid,max(ssid) FROM gbobjects  where ssid<= 100000  group by nid  ;