Hello
a very ugly test shows a possibility about 100% speedup on reported example (on small arrays, a patch is buggy and doesn't work for larger arrays).
I updated a code to be read only
CREATE OR REPLACE FUNCTION public.fill_2d_array(rows integer, cols integer)
RETURNS integer
LANGUAGE plpgsql
AS $function$
DECLARE
img double precision[][];
i integer; j integer;
cont integer; r double precision;
BEGIN
img := ARRAY( SELECT 0 FROM generate_series(1, rows * cols) ) ;
cont:= 0;
For i IN 1..rows LOOP
For j IN 1..cols LOOP r := img[i * cols + j];
r := (i * cols + j)::double precision;
cont := cont + 1; --raise notice '%', img;
END LOOP;
END LOOP;
return cont;
END;
$function$
It exec all expressions
-- original
postgres=# select fill_2d_array(200,200);
fill_2d_array
---------------
40000
(1 row)
Time: 12726.117 ms
-- read only version
postgres=# select fill_2d_array(200,200); fill_2d_array
---------------
40000
(1 row)
Time: 245.894 ms
so there is about 50x slowdown
