Помогите, пожалуйста, максимально оптимизировать функцию по времени выполнения.

CREATE OR REPLACE FUNCTION public.graph_calculatepath (
graphtype public.graphtype,
source integer,
target integer,
prohibited public.geometry,
band public.geometry,
pathtype public.pathtype
)
RETURNS SETOF public.pathedge AS
$body$
DECLARE

sql TEXT;
algo TEXT;

point INTEGER;
seq INTEGER;

pathedge public.pathedge;
edges TEXT = lower(graphtype::TEXT) || '.edges';
addedges TEXT = lower(graphtype::TEXT) || '_addedges';
deledges TEXT = lower(graphtype::TEXT) || '_deledges';
delnodes TEXT = lower(graphtype::TEXT) || '_delnodes';

BEGIN

IF (source != 0) AND (target != 0) AND (source != target) THEN

algo := graph_casepathsalgorithm(pathtype);

-- Shortest path query
sql := 'SELECT paths.seq, edges.* '
||'FROM '|| algo ||' (''SELECT * FROM (SELECT * FROM ' || addedges
||' UNION ALL SELECT * FROM ' || edges || ') AS graph '
||'WHERE id NOT IN (SELECT gid FROM ' || deledges || ') '
|| 'AND source NOT IN (SELECT gid FROM ' || delnodes || ') '
|| 'AND target NOT IN (SELECT gid FROM ' || delnodes || ') '
|| CASE WHEN prohibited IS NOT NULL THEN
'AND NOT st_intersects(the_geom, '
|| 'geomfromewkt('''||quote_literal(st_asewkt(prohibited))||''')) '
ELSE '' END
|| CASE WHEN band IS NOT NULL THEN
'AND st_intersects(the_geom, '
|| 'geomfromewkt('''||quote_literal(st_asewkt(band))||''')) '
ELSE '' END
||''', ' || source || ', ' || target
||', false, false) AS paths, '
||'(SELECT * FROM ' || addedges
||' UNION ALL SELECT * FROM ' || edges || ') AS edges '
||'WHERE paths.id2 = edges.id '
||'ORDER BY seq;';

-- Remember start point
point := source;
seq := 0;

BEGIN

FOR pathedge IN EXECUTE sql
LOOP
-- Flip geometry (if required)
IF ( point != pathedge.source ) THEN
pathedge.the_geom := st_reverse(pathedge.the_geom);
point := pathedge.source;
pathedge.source := pathedge.target;
pathedge.target := point;
ELSE
point := pathedge.target;
END IF;

-- Return record
pathedge.seq := seq;
RETURN NEXT pathedge;
seq := seq + 1;
END LOOP; -- FOR pathedge IN EXECUTE sql

EXCEPTION WHEN OTHERS THEN
RAISE NOTICE '%: graph_calculatepath: PATH NOT FOUND!', upper(pathtype::TEXT);
RAISE NOTICE 'NUM: %, DETAILS: %', SQLSTATE, SQLERRM;
RETURN;

END;

END IF; -- IF (source != 0) AND (target != 0) THEN

RETURN;
END;
$body$
LANGUAGE 'plpgsql'
VOLATILE
CALLED ON NULL INPUT
SECURITY INVOKER
COST 100 ROWS 1000;

Помогите, пожалуйста, максимально оптимизировать функцию по времени выполнения.