Possible to improve query plan?

Hi all,

I've come to a dead end in trying to get a commonly used query to perform better. The query is against one table with
10million rows. This table has been analysed. The table definition is: 

CREATE TABLE version_crs_coordinate_revision
(
  _revision_created integer NOT NULL,
  _revision_expired integer,
  id integer NOT NULL,
  cos_id integer NOT NULL,
  nod_id integer NOT NULL,
  ort_type_1 character varying(4),
  ort_type_2 character varying(4),
  ort_type_3 character varying(4),
  status character varying(4) NOT NULL,
  sdc_status character(1) NOT NULL,
  source character varying(4),
  value1 numeric(22,12),
  value2 numeric(22,12),
  value3 numeric(22,12),
  wrk_id_created integer,
  cor_id integer,
  audit_id integer NOT NULL,
  CONSTRAINT pkey_version_crs_coordinate_revision PRIMARY KEY (_revision_created, id),
  CONSTRAINT version_crs_coordinate_revision_revision_created_fkey FOREIGN KEY (_revision_created)
      REFERENCES revision (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT version_crs_coordinate_revision_revision_expired_fkey FOREIGN KEY (_revision_expired)
      REFERENCES revision (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
)
WITH (
  OIDS=FALSE
);
ALTER TABLE "version".version_crs_coordinate_revision ALTER COLUMN _revision_created SET STATISTICS 1000;
ALTER TABLE "version".version_crs_coordinate_revision ALTER COLUMN _revision_expired SET STATISTICS 1000;
ALTER TABLE "version".version_crs_coordinate_revision ALTER COLUMN id SET STATISTICS 1000;

CREATE INDEX idx_crs_coordinate_revision_created ON "version".version_crs_coordinate_revision USING btree
(_revision_created);
CREATE INDEX idx_crs_coordinate_revision_created_expired ON "version".version_crs_coordinate_revision USING btree
(_revision_created,_revision_expired); 
CREATE INDEX idx_crs_coordinate_revision_expired ON "version".version_crs_coordinate_revision USING btree
(_revision_expired);
CREATE INDEX idx_crs_coordinate_revision_expired_created ON "version".version_crs_coordinate_revision USING btree
(_revision_expired,_revision_created); 
CREATE INDEX idx_crs_coordinate_revision_expired_id ON "version".version_crs_coordinate_revision USING btree
(_revision_expired,id); 
CREATE INDEX idx_crs_coordinate_revision_id ON "version".version_crs_coordinate_revision USING btree (id);
CREATE INDEX idx_crs_coordinate_revision_id_created ON "version".version_crs_coordinate_revision USING btree (id,
_revision_created); 


The distribution of the data is that all but 120,000 rows have null values in the _revision_expired column.

The query itself that I'm trying to optimise is below:

EXPLAIN
SELECT * FROM (
    SELECT
        row_number() OVER (PARTITION BY id ORDER BY _revision_created DESC) as row_number,
        *
    FROM
        version_crs_coordinate_revision
    WHERE (
        (_revision_created <= 16 AND _revision_expired > 16 AND _revision_expired <= 40) OR
        (_revision_created > 16 AND _revision_created <= 40)
    )
) AS T
WHERE row_number = 1;

Subquery Scan t  (cost=170692.25..175678.27 rows=767 width=205)
  Filter: (t.row_number = 1)
  ->  WindowAgg  (cost=170692.25..173760.57 rows=153416 width=86)
        ->  Sort  (cost=170692.25..171075.79 rows=153416 width=86)
              Sort Key: version_crs_coordinate_revision.id, version_crs_coordinate_revision._revision_created
              ->  Bitmap Heap Scan on version_crs_coordinate_revision  (cost=3319.13..157477.69 rows=153416 width=86)
                    Recheck Cond: (((_revision_expired > 16) AND (_revision_expired <= 40)) OR ((_revision_created >
16)AND (_revision_created <= 40))) 
                    Filter: (((_revision_created <= 16) AND (_revision_expired > 16) AND (_revision_expired <= 40)) OR
((_revision_created> 16) AND (_revision_created <= 40))) 
                    ->  BitmapOr  (cost=3319.13..3319.13 rows=154372 width=0)
                          ->  Bitmap Index Scan on idx_crs_coordinate_revision_expired  (cost=0.00..2331.76 rows=111041
width=0)
                                Index Cond: ((_revision_expired > 16) AND (_revision_expired <= 40))
                          ->  Bitmap Index Scan on idx_crs_coordinate_revision_created  (cost=0.00..910.66 rows=43331
width=0)
                                Index Cond: ((_revision_created > 16) AND (_revision_created <= 40))


One thought I have is that maybe the idx_crs_coordinate_revision_expired_created index could be used instead of
idx_crs_coordinate_revision_expired.

Does anyone have any suggestions what I could do to improve the plan? Or how I could force the use of the
idx_crs_coordinate_revision_expired_createdindex to see if that is better. 

Thanks
Jeremy


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