-- sift.workers lists a sift_table next to the indexes: index is the table, kind sift_table, its directory entries and sealed write buffers are counted,
-- and the columns that note a failed background step are 0 and NULL (the background of a table keeps no note). worker_state refuses anything else.
SET client_min_messages = warning;
CREATE EXTENSION pg_sift;
CREATE TABLE tw (id int, g int, v float8) USING sift_table;
CREATE TABLE tp (id int, g int);
CREATE INDEX tp_col ON tp USING sift_col (id, g);
INSERT INTO tw SELECT i, i % 10, i FROM generate_series(1, 5000) i;
INSERT INTO tp SELECT i, i % 10 FROM generate_series(1, 100) i;
SELECT index, kind, segments >= 1 AS has_segments, sealed >= 0 AS has_sealed, failures, failed_at, next_retry, error_code, last_error, due
FROM sift.workers ORDER BY 1::text;
 index  |    kind    | has_segments | has_sealed | failures | failed_at | next_retry | error_code | last_error | due 
--------+------------+--------------+------------+----------+-----------+------------+------------+------------+-----
 tp_col | sift_col   | t            | t          |        0 |           |            |            |            | 
 tw     | sift_table | t            | t          |        0 |           |            |            |            | 
(2 rows)

SELECT segments = (SELECT count(*) FROM sift.table_segments('tw')) AS same_segments FROM sift.worker_state('tw');
 same_segments 
---------------
 t
(1 row)

SELECT * FROM sift.worker_state('pg_class');
ERROR:  "pg_class" is not a sift index
SELECT * FROM sift.worker_state('tp');
ERROR:  "tp" is not a sift index
-- a role that cannot read the table does not see it
CREATE ROLE tw_reader NOLOGIN;
SET ROLE tw_reader;
SELECT count(*) AS rows_seen FROM sift.workers;
 rows_seen 
-----------
         0
(1 row)

RESET ROLE;
GRANT SELECT ON tw TO tw_reader;
SET ROLE tw_reader;
SELECT index, kind FROM sift.workers;
 index |    kind    
-------+------------
 tw    | sift_table
(1 row)

RESET ROLE;
DROP TABLE tw, tp;
DROP ROLE tw_reader;
DROP EXTENSION pg_sift;