CREATE TABLE pg_temp.parts
(
    seid             bigint,
    r_field_name_1   smallint,
    fr_field_name    smallint           NOT NULL,
    p1_field_name    varchar(4),
    qty_field_name   integer,
    p5_field_name    varchar(30),
    partnum          varchar(30),
    st_field_name    smallint DEFAULT 0 NOT NULL
); -- drop table pg_temp.parts;

INSERT INTO pg_temp.parts (seid, partnum, qty_field_name, fr_field_name, st_field_name)
SELECT (RANDOM() * 3821 + 1)::bigint                                   AS seid,
       (RANDOM() * 123456789)::text                                    AS partnum,
       CASE
           WHEN q.rnd BETWEEN 0 AND 0.45 THEN FLOOR(RANDOM() * 900) + 100 -- Random number in the range [100, 999]
           WHEN q.rnd BETWEEN 0.46 AND 0.96 THEN LEAST(TRUNC(FLOOR(RANDOM() * 999999) + 1000)::int, 999999::int) -- Random number in the range [1000, 9999]
           ELSE FLOOR(RANDOM() * 9000000) + 1000000 -- Random number in the range [100000, 999999]
           END                                                         AS qty_field_name,
       CASE WHEN RANDOM() < 0.72 THEN 0::smallint ELSE 1::smallint END AS fr_field_name,
       CASE WHEN RANDOM() < 0.46 THEN 1::smallint ELSE 2::smallint END AS st_field_name
  FROM (SELECT RANDOM() AS rnd, x FROM GENERATE_SERIES(1, 90_000_000) x) q;

CREATE INDEX idx_parts_supid ON pg_temp.parts USING btree (seid, p1_field_name, partnum, st_field_name, r_field_name_1, qty_field_name);
CREATE INDEX idx_parts_p5 ON pg_temp.parts USING btree (p5_field_name, seid, st_field_name, r_field_name_1, p1_field_name);
CREATE INDEX idx_parts_partnum ON pg_temp.parts USING btree (partnum, seid, st_field_name, r_field_name_1, p1_field_name);

CREATE OR REPLACE FUNCTION pg_temp.fx(asupplier bigint = 497 )
    RETURNS void
    LANGUAGE plpgsql
AS
$function$
DECLARE
    supplier_parts       CURSOR (sid bigint) FOR  -- Again, selecting with COUNT() would reduce 1 query per row!
        SELECT
            partnum, qty_field_name, st_field_name, sum(qty_field_name) as qty
            FROM pg_temp.parts
            WHERE seid = sid AND (st_field_name = 1)
            GROUP BY partnum, qty_field_name, st_field_name
            ORDER BY partnum, qty_field_name, st_field_name;
    supplier_part_qty_matches CURSOR (sid bigint, pnum varchar(30), pqty bigint) FOR
        SELECT DISTINCT
            seid, fr_field_name, partnum, st_field_name
            FROM pg_temp.parts
            WHERE seid <> sid AND partnum = pnum AND qty_field_name = pqty
            ORDER BY seid, partnum;

    a_partnum     varchar(30);
    a_qty         integer;
    a_st          smallint;
    a_cnt         integer = 0;
    b_partnum     varchar(30);
    b_fr          smallint;
    b_seid        bigint;
    b_st          smallint;
    b_cnt         bigint = 0;
BEGIN
    RAISE NOTICE '%', (SELECT (PG_SIZE_PRETTY(SUM(used_bytes)), PG_SIZE_PRETTY(SUM(total_bytes)), PG_SIZE_PRETTY(SUM(free_bytes))) FROM pg_get_backend_memory_contexts());
    OPEN supplier_parts (asupplier);
    LOOP
        FETCH supplier_parts INTO a_partnum, a_qty, a_st, a_qty;
        EXIT WHEN NOT FOUND;
        a_cnt := a_cnt + 1;
        OPEN supplier_part_qty_matches (sid := asupplier, pnum := a_partnum, pqty := a_qty);
        LOOP
            FETCH supplier_part_qty_matches INTO b_seid, b_fr, b_partnum, b_st;
            b_cnt := b_cnt + 1;
            EXIT WHEN TRUE;  -- no Need to loop here  One FETCH per query triggers the losses.
        END LOOP;
        CLOSE supplier_part_qty_matches;
    END LOOP;
    CLOSE supplier_parts;
    RAISE NOTICE '-----------after close, Count a: %, count b: %', a_cnt, b_cnt;
    RAISE NOTICE '%', (SELECT (PG_SIZE_PRETTY(SUM(used_bytes)), PG_SIZE_PRETTY(SUM(total_bytes)), PG_SIZE_PRETTY(SUM(free_bytes))) FROM pg_get_backend_memory_contexts());
    --perform meminfo();
END;
$function$;

-- This will use JIT until the table is analyzed, which causes the problem
explain SELECT DISTINCT seid, fr_field_name, st_field_name
          FROM pg_temp.parts
         WHERE seid <> 497 AND partnum >= '1'
         ORDER BY seid;

-- But using JIT results in loss of some bytes.
SELECT pg_temp.fx(497);