DO $$
DECLARE
    v_version numeric;
BEGIN

    SELECT substring(setting from '\d+')::numeric INTO v_version FROM pg_settings WHERE name = 'server_version';

    -- GUCs common for all versions
    PERFORM set_config('extra_float_digits', '0', false);
    PERFORM set_config('parallel_setup_cost', '0', false);
    PERFORM set_config('parallel_tuple_cost', '0', false);
    PERFORM set_config('max_parallel_workers_per_gather', '2', false);

    -- 9.6 used somewhat different GUC name for relation size
    IF v_version < 10 THEN
        PERFORM set_config('min_parallel_relation_size', '1kB', false);
    ELSE
        PERFORM set_config('min_parallel_table_scan_size', '1kB', false);
    END IF;

    -- in 14 disable Memoize nodes, to make explain more consistent
    IF v_version >= 14 THEN
        PERFORM set_config('enable_memoize', 'off', false);
    END IF;

END;
$$ LANGUAGE plpgsql;

-- test incremental API (adding values one by one)
CREATE TABLE t (d tdigest);
INSERT INTO t VALUES (NULL);

-- check this produces the same result building the tdigest at once, but we
-- need to be careful about feeding the data in the same order, and we must
-- not compactify the t-digest after each increment
DO LANGUAGE plpgsql $$
DECLARE
  r RECORD;
BEGIN
    FOR r IN (SELECT i FROM generate_series(1,1000) s(i) ORDER BY md5(i::text)) LOOP
        UPDATE t SET d = tdigest_add(d, r.i, 100, false);
    END LOOP;
END$$;

-- compare the results, but do force a compaction of the incremental result
WITH x AS (SELECT i FROM generate_series(1,1000) s(i) ORDER BY md5(i::text))
SELECT (SELECT tdigest(d)::text FROM t) = (SELECT tdigest(x.i, 100)::text FROM x) AS match;

-- now try the same thing with bulk incremental update (using arrays)
TRUNCATE t;
INSERT INTO t VALUES (NULL);

DO LANGUAGE plpgsql $$
DECLARE
  r RECORD;
BEGIN
    FOR r IN (SELECT a, array_agg(i::double precision) AS v FROM (SELECT mod(i,5) AS a, i FROM generate_series(1,1000) s(i) ORDER BY mod(i,5), md5(i::text)) foo GROUP BY a ORDER BY a) LOOP
        UPDATE t SET d = tdigest_add(d, r.v, 100, false);
    END LOOP;
END$$;

-- compare the results, but do force a compaction of the incremental result
WITH x AS (SELECT mod(i,5) AS a, i::double precision AS d FROM generate_series(1,1000) s(i) ORDER BY mod(i,5), i)
SELECT (SELECT tdigest(d)::text FROM t) = (SELECT tdigest(x.d, 100)::text FROM x);

-- now try the same thing with bulk incremental update (using t-digests)
TRUNCATE t;
INSERT INTO t VALUES (NULL);

DO LANGUAGE plpgsql $$
DECLARE
  r RECORD;
BEGIN
    FOR r IN (SELECT a, tdigest(i,100) AS d FROM (SELECT mod(i,5) AS a, i FROM generate_series(1,1000) s(i) ORDER BY mod(i,5), md5(i::text)) foo GROUP BY a ORDER BY a) LOOP
        UPDATE t SET d = tdigest_union(d, r.d, false);
    END LOOP;
END$$;

-- compare the results, but do force a compaction of the incremental result
WITH x AS (SELECT a, tdigest(i,100) AS d FROM (SELECT mod(i,5) AS a, i FROM generate_series(1,1000) s(i) ORDER BY mod(i,5), md5(i::text)) foo GROUP BY a ORDER BY a)
SELECT (SELECT tdigest(d)::text FROM t) = (SELECT tdigest(x.d)::text FROM x);