-- The statistics of a column index that a plan reads are kept by the backend between plans, as of the state of the index (its directory version, the
-- pages of the table and those all-visible, the catalog entries of the index and the table). A plan after a change of any of these prices the scan
-- with the new facts, and sift.plan_scale, applied to the copy a plan takes, changes the price without a change of the index.
CREATE EXTENSION pg_sift;
SET max_parallel_workers_per_gather = 0;
SET sift.agg_force = off;
CREATE TABLE ev (id int, grp int, v int) WITH (autovacuum_enabled = false);
INSERT INTO ev SELECT i, i % 50, i % 7 FROM generate_series(1, 20000) i;
CREATE INDEX ev_col ON ev USING sift_col (id, grp, v);
VACUUM (FREEZE, ANALYZE) ev;

-- the price of the scan node of the grouped query, as the planner gives it with the normal paths off
CREATE FUNCTION scan_price() RETURNS numeric LANGUAGE plpgsql AS $$
DECLARE l text; p numeric;
BEGIN
	SET LOCAL enable_seqscan = off; SET LOCAL enable_indexscan = off; SET LOCAL enable_bitmapscan = off; SET LOCAL enable_indexonlyscan = off;
	FOR l IN EXECUTE 'EXPLAIN SELECT grp, sum(v) FROM ev GROUP BY grp' LOOP
		IF l ~ 'Custom Scan \(SiftAgg\)' THEN p := substring(l from '\.\.([0-9.]+) rows')::numeric; END IF;
	END LOOP;
	RETURN p;
END $$;

CREATE TABLE price (step text, p numeric);
INSERT INTO price SELECT 'start', scan_price();
INSERT INTO price SELECT 'same', scan_price();
INSERT INTO ev SELECT i, i % 50, i % 7 FROM generate_series(20001, 400000) i;
VACUUM (FREEZE, ANALYZE) ev;
INSERT INTO price SELECT 'after growth', scan_price();
SET sift.plan_scale = 10;
INSERT INTO price SELECT 'scaled', scan_price();
RESET sift.plan_scale;
INSERT INTO price SELECT 'unscaled again', scan_price();
REINDEX INDEX ev_col;
INSERT INTO price SELECT 'after reindex', scan_price();

SELECT (SELECT p FROM price WHERE step = 'start') = (SELECT p FROM price WHERE step = 'same') AS same_state_same_price,
       (SELECT p FROM price WHERE step = 'after growth') > (SELECT p FROM price WHERE step = 'start') AS grows_with_the_index,
       (SELECT p FROM price WHERE step = 'scaled') > (SELECT p FROM price WHERE step = 'after growth') AS scale_applies,
       (SELECT p FROM price WHERE step = 'unscaled again') = (SELECT p FROM price WHERE step = 'after growth') AS scale_leaves_no_trace,
       (SELECT p FROM price WHERE step = 'after reindex') > 0 AS priced_after_reindex;
DROP FUNCTION scan_price();
DROP TABLE price, ev;
DROP EXTENSION pg_sift;