postgres/contrib/pageinspect/sql/gin.sql

CREATE TABLE test1 (x int, y int[]);
INSERT INTO test1 VALUES (1, ARRAY[11, 111]);
CREATE INDEX test1_y_idx ON test1 USING gin (y) WITH (fastupdate = off);

\x

SELECT * FROM gin_metapage_info(get_raw_page('test1_y_idx', 0));
SELECT * FROM gin_metapage_info(get_raw_page('test1_y_idx', 1));

SELECT * FROM gin_page_opaque_info(get_raw_page('test1_y_idx', 1));

SELECT * FROM gin_leafpage_items(get_raw_page('test1_y_idx', 1));

INSERT INTO test1 SELECT x, ARRAY[1,10] FROM generate_series(2,10000) x;

SELECT COUNT(*) > 0
FROM gin_leafpage_items(get_raw_page('test1_y_idx',
                        (pg_relation_size('test1_y_idx') /
                         current_setting('block_size')::bigint)::int - 1));