-- New rows of a key_cut index in partitions are promoted into a segment that holds rows of every key. Once it is as large as half a partition it overlaps
-- every partition, as the runs of a build do, but it is a few percent of the index and the rewrite that takes it in rewrites all the partitions it meets:
-- that is churn, which waits for the WAL budget, and not the build's rewrite, which does not.
CREATE EXTENSION pg_sift;
SET client_min_messages = warning;
SET max_parallel_workers_per_gather = 0;
SET max_parallel_maintenance_workers = 0;
SET sift.async_maintenance = off;
SET sift.vacuum_rewrite_limit = 1;
SET sift.col_auto_merge_partition_kb = 512;
SET sift.col_auto_merge_wal_pct = 5;
SET sift.test_col_segment_kb = 7000;
SET sift.col_build_key_ranges = off;

CREATE TABLE go (id int, tenant_id int, d date, amount int, pad text) WITH (autovacuum_enabled = false);
INSERT INTO go SELECT i, (i * 7919) % 400, date '2026-01-01' + (i * 31) % 300, i % 100, md5(i::text) || md5((i + 1)::text) || md5((i + 2)::text) FROM generate_series(1, 168960) i;
VACUUM (FREEZE, ANALYZE) go;
CREATE INDEX go_idx ON go USING sift_col (id, tenant_id, d, amount, pad) WITH (key_cut = 'tenant_id', dict_lookup = off);

-- the runs of the build overlap each other and are the index: their rewrite is due at once, whatever the WAL budget
SELECT sift.col_maintenance_due('go_idx', true) AS build_due;
SELECT sift.col_maintain('go_idx') AS partitioned;
SELECT sift.col_maintenance_due('go_idx', true) AS due_after_build;

-- 12,000 new rows over all the tenants, promoted: a segment of at least half a partition that meets every partition, 6% of the index
INSERT INTO go SELECT 200000 + i, (i * 7919) % 400, date '2026-01-01' + (i * 31) % 300, i % 100, md5(i::text) || md5((i + 1)::text) || md5((i + 2)::text) FROM generate_series(1, 12000) i;
SELECT sift.col_promote('go_idx');
SELECT count(*) FILTER (WHERE bytes * 2 >= 512 * 1024) AS overlay_partition_sized
  FROM sift.col_segments('go_idx') WHERE kind = 'immutable' AND rows = 12000;

-- the automatic rewrite waits for the WAL of the churn that makes it worth its bytes; the manual rule still sees the overlap
SELECT sift.col_maintenance_due('go_idx', true) AS due_automatic;
SELECT sift.col_maintenance_due('go_idx', false) AS due_manual;
SELECT sift.col_maintain('go_idx') AS rewritten;
SELECT sift.col_verify('go_idx', true);
SELECT sift.col_maintenance_due('go_idx', false) AS due_again;
DROP TABLE go;
DROP EXTENSION pg_sift;