CREATE TABLE test1 (a int8, b text);
INSERT INTO test1 VALUES (72057594037927937, 'text');
CREATE INDEX test1_a_idx ON test1 USING btree (a);
\x
SELECT * FROM bt_metap('test1_a_idx');
-[ RECORD 1 ]-------------+-------
magic                     | 340322
version                   | 4
root                      | 1
level                     | 0
fastroot                  | 1
fastlevel                 | 0
last_cleanup_num_delpages | 0
last_cleanup_num_tuples   | -1
allequalimage             | t

SELECT * FROM bt_page_stats('test1_a_idx', -1);
ERROR:  invalid block number
SELECT * FROM bt_page_stats('test1_a_idx', 0);
ERROR:  block 0 is a meta page
SELECT * FROM bt_page_stats('test1_a_idx', 1);
-[ RECORD 1 ]-+-----
blkno         | 1
type          | l
live_items    | 1
dead_items    | 0
avg_item_size | 16
page_size     | 8192
free_size     | 8128
btpo_prev     | 0
btpo_next     | 0
btpo_level    | 0
btpo_flags    | 3

SELECT * FROM bt_page_stats('test1_a_idx', 2);
ERROR:  block number out of range
SELECT * FROM bt_page_items('test1_a_idx', -1);
ERROR:  invalid block number
SELECT * FROM bt_page_items('test1_a_idx', 0);
ERROR:  block 0 is a meta page
SELECT * FROM bt_page_items('test1_a_idx', 1);
-[ RECORD 1 ]-----------------------
itemoffset | 1
ctid       | (0,1)
itemlen    | 16
nulls      | f
vars       | f
data       | 01 00 00 00 00 00 00 01
dead       | f
htid       | (0,1)
tids       | 

SELECT * FROM bt_page_items('test1_a_idx', 2);
ERROR:  block number out of range
SELECT * FROM bt_page_items(get_raw_page('test1_a_idx', -1));
ERROR:  invalid block number
SELECT * FROM bt_page_items(get_raw_page('test1_a_idx', 0));
ERROR:  block is a meta page
SELECT * FROM bt_page_items(get_raw_page('test1_a_idx', 1));
-[ RECORD 1 ]-----------------------
itemoffset | 1
ctid       | (0,1)
itemlen    | 16
nulls      | f
vars       | f
data       | 01 00 00 00 00 00 00 01
dead       | f
htid       | (0,1)
tids       | 

SELECT * FROM bt_page_items(get_raw_page('test1_a_idx', 2));
ERROR:  block number 2 is out of range for relation "test1_a_idx"
DROP TABLE test1;