-- The rewrite of every segment decides again what a build decides from the data (key_cut, the order arrays, the point directories of the options the build chose),
-- so an index built on a table in the order of its tenants and rewritten after rows of every tenant were appended is as small as a rebuild of it
--: the maintained size is within 5% of the REINDEX of the same rows, the answers are the table's, and the choice is the build's.
CREATE EXTENSION pg_sift;
SET sift.test_col_net = off;	-- this test is of the dirty units and their rewrite (col_net_agg is of the sidecar VACUUM writes for them)
SET client_min_messages = warning;
SET max_parallel_workers_per_gather = 0;
SET max_parallel_maintenance_workers = 0;
SET sift.col_auto_merge = off;
SET sift.async_maintenance = off;	-- no worker takes the steps below (col_key_cut_redecide_async is the same rewrite with it on)
SET sift.col_wbuf_ref = off;	-- a buffer of references holds more rows at its limit, so VACUUM promotes it whole and leaves the second index nothing to rewrite (col_wbuf_arena* test the references)

CREATE TABLE rc (id int PRIMARY KEY, tenant_id int, foreign_id int, counter_a int, updated_at timestamp, pad text);
INSERT INTO rc SELECT i, i / 150, 1 + i % 12, hashint4(i) & 1048575, TIMESTAMP '2026-01-01' + (hashint4(i + 7) & 16777215) * INTERVAL '1 second', repeat('x', 100)
FROM generate_series(1, 120000) i;
VACUUM ANALYZE rc;
CREATE INDEX rc_ix ON rc USING sift_col (id, tenant_id, foreign_id, counter_a, updated_at) WITH (dead_rewrite_pct = 50);
-- the same columns with the key the user wrote
CREATE INDEX rc_off ON rc USING sift_col (id, tenant_id, foreign_id, counter_a, updated_at) WITH (key_cut = 'off');
-- built on rows in the order of the tenants: no cut
SELECT reloptions::text ~ 'key_cut' AS cut_at_build FROM pg_class WHERE relname = 'rc_ix';

-- rows of every tenant appended at the end of the heap, a tenth of the rows deleted
INSERT INTO rc SELECT i, (hashint4(i) & 2147483647) % 800, 1 + i % 12, hashint4(i) & 1048575, TIMESTAMP '2026-01-01' + (hashint4(i + 7) & 16777215) * INTERVAL '1 second', repeat('x', 100)
FROM generate_series(120001, 240000) i;
DELETE FROM rc WHERE id % 10 = 3;
VACUUM ANALYZE rc;
-- the NOTICE names the choice as the option holds it
SET client_min_messages = notice;
\set VERBOSITY terse
SELECT sift.col_maintain('rc_ix');
\set VERBOSITY default
SET client_min_messages = warning;
SELECT sift.col_maintain('rc_off');
VACUUM rc;
VACUUM rc;
SELECT pg_relation_size('rc_ix') AS maintained \gset
SELECT reloptions::text ~ 'key_cut=auto: foreign_id' AS cut_after_rewrite FROM pg_class WHERE relname = 'rc_ix';
SELECT sift.col_verify('rc_ix');
-- an option the user wrote is not changed by the rewrite
SELECT reloptions::text ~ 'key_cut=off' AND reloptions::text !~ 'key_cut=auto' AS user_option_kept FROM pg_class WHERE relname = 'rc_off';
DROP INDEX rc_off;

-- the answers are the table's
SELECT count(*) AS n, sum(counter_a) AS s, count(DISTINCT tenant_id) AS t FROM rc WHERE foreign_id = 5 \gset maint_
SET sift.enable_agg = off;
SELECT count(*) = :maint_n AND sum(counter_a) = :maint_s AND count(DISTINCT tenant_id) = :maint_t AS same_answers FROM rc WHERE foreign_id = 5;
RESET sift.enable_agg;

REINDEX INDEX rc_ix;
SELECT pg_relation_size('rc_ix') AS rebuilt \gset
SELECT :maintained <= :rebuilt * 1.05 AS maintained_within_5_percent;

DROP TABLE rc;
DROP EXTENSION pg_sift;