-- an update that leaves the indexed text alone adds a document to the index when it is not HOT: the new row version has
-- its own TID, which is what the index finds documents by (indexUnchanged cannot let aminsert skip it); a HOT update adds none
CREATE EXTENSION pg_sift;

CREATE FUNCTION wbuf_docs(idx regclass) RETURNS bigint LANGUAGE sql AS
	$$ SELECT coalesce(sum(ndocs), 0)::bigint FROM sift.segments(idx) WHERE kind <> 'immutable' $$;

-- room in every page (fillfactor): the updates are HOT, the index is not touched
CREATE TABLE wu_hot (id int PRIMARY KEY, body text, n int) WITH (fillfactor = 40, autovacuum_enabled = off);
INSERT INTO wu_hot SELECT i, 'alpha beta ' || i, 0 FROM generate_series(1, 300) i;
CREATE INDEX wu_hot_idx ON wu_hot USING sift (body);
BEGIN;
UPDATE wu_hot SET n = n + 1;
SELECT pg_stat_get_xact_tuples_hot_updated('wu_hot'::regclass) AS hot_updates, wbuf_docs('wu_hot_idx') AS index_entries;
COMMIT;
SELECT count(*) FROM wu_hot WHERE body @@> 'alpha';

-- full pages: the updates that do not fit are not HOT and each adds a document, though the text is unchanged
CREATE TABLE wu_cold (id int PRIMARY KEY, body text, n int) WITH (fillfactor = 100, autovacuum_enabled = off);
INSERT INTO wu_cold SELECT i, 'alpha beta ' || i, 0 FROM generate_series(1, 300) i;
CREATE INDEX wu_cold_idx ON wu_cold USING sift (body);
BEGIN;
UPDATE wu_cold SET n = n + 1;
SELECT pg_stat_get_xact_tuples_hot_updated('wu_cold'::regclass) < 300 AS some_not_hot,
	wbuf_docs('wu_cold_idx') = 300 - pg_stat_get_xact_tuples_hot_updated('wu_cold'::regclass) AS one_entry_per_not_hot;
COMMIT;
SELECT count(*) FROM wu_cold WHERE body @@> 'alpha';

DROP TABLE wu_hot, wu_cold;
DROP FUNCTION wbuf_docs(regclass);
DROP EXTENSION pg_sift;