pageinspect插件可以用来查看表和索引的内部结构，但并不是所有的索引类型都支持，PG14中增加了三个函数用来支持对gist索引的支持。
function gist_page_items(bytea,regclass)
function gist_page_items_bytea(bytea)
function gist_page_opaque_info(bytea)
例子：
创建测试表和索引：
bill@bill=>CREATE TABLE test_gist AS SELECT point(i,i) p, i::text t FROM
bill-# generate_series(1,1000) i;
SELECT 1000
bill@bill=> CREATE INDEX test_gist_idx ON test_gist USING gist (p);
CREATE INDEX
使用pageinspect观察gist索引结构：
bill@bill=> SELECT * FROM gist_page_opaque_info(get_raw_page('test_gist_idx', 0));
lsn | nsn | rightlink | flags
-----+-----+------------+-------
0/1 | 0/0 | 4294967295 | {}
(1 row)
bill@bill=> SELECT * FROM gist_page_opaque_info(get_raw_page('test_gist_idx', 1));
lsn | nsn | rightlink | flags
-----+-----+------------+--------
0/1 | 0/0 | 4294967295 | {leaf}
(1 row)
bill@bill=> SELECT * FROM gist_page_opaque_info(get_raw_page('test_gist_idx', 2));
lsn | nsn | rightlink | flags
-----+-----+-----------+--------
0/1 | 0/0 | 1 | {leaf}
(1 row)
bill@bill=> SELECT * FROM gist_page_items(get_raw_page('test_gist_idx', 0), 'test_gist_idx');
itemoffset | ctid | itemlen | dead | keys
------------+-----------+---------+------+-------------------
1 | (1,65535) | 40 | f | (p)=((166,166))
2 | (2,65535) | 40 | f | (p)=((332,332))
3 | (3,65535) | 40 | f | (p)=((498,498))
4 | (4,65535) | 40 | f | (p)=((664,664))
5 | (5,65535) | 40 | f | (p)=((830,830))
6 | (6,65535) | 40 | f | (p)=((996,996))
7 | (7,65535) | 40 | f | (p)=((1000,1000))
(7 rows)
bill@bill=> SELECT * FROM gist_page_items(get_raw_page('test_gist_idx', 1), 'test_gist_idx') LIMIT 5;
itemoffset | ctid | itemlen | dead | keys
------------+-------+---------+------+-------------
1 | (0,1) | 40 | f | (p)=((1,1))
2 | (0,2) | 40 | f | (p)=((2,2))
3 | (0,3) | 40 | f | (p)=((3,3))
4 | (0,4) | 40 | f | (p)=((4,4))
5 | (0,5) | 40 | f | (p)=((5,5))
(5 rows)
bill@bill=> SELECT * FROM gist_page_items(get_raw_page('test_gist_idx', 2), 'test_gist_idx') LIMIT 5;
itemoffset | ctid | itemlen | dead | keys
------------+--------+---------+------+-----------------
1 | (1,10) | 40 | f | (p)=((167,167))
2 | (1,11) | 40 | f | (p)=((168,168))
3 | (1,12) | 40 | f | (p)=((169,169))
4 | (1,13) | 40 | f | (p)=((170,170))
5 | (1,14) | 40 | f | (p)=((171,171))
(5 rows)
bill@bill=> SELECT * FROM gist_page_items_bytea(get_raw_page('test_gist_idx', 0));
itemoffset | ctid | itemlen | dead | key_data
------------+-----------+---------+------+------------------------------------------------------------------------------------
1 | (1,65535) | 40 | f | \x00000100ffff28000000000000c064400000000000c06440000000000000f03f000000000000f03f
2 | (2,65535) | 40 | f | \x00000200ffff28000000000000c074400000000000c074400000000000e064400000000000e06440
3 | (3,65535) | 40 | f | \x00000300ffff28000000000000207f400000000000207f400000000000d074400000000000d07440
4 | (4,65535) | 40 | f | \x00000400ffff28000000000000c084400000000000c084400000000000307f400000000000307f40
5 | (5,65535) | 40 | f | \x00000500ffff28000000000000f089400000000000f089400000000000c884400000000000c88440
6 | (6,65535) | 40 | f | \x00000600ffff28000000000000208f400000000000208f400000000000f889400000000000f88940
7 | (7,65535) | 40 | f | \x00000700ffff28000000000000408f400000000000408f400000000000288f400000000000288f40
(7 rows)
bill@bill=> SELECT * FROM gist_page_items_bytea(get_raw_page('test_gist_idx', 1)) LIMIT 5;
itemoffset | ctid | itemlen | dead | key_data
------------+-------+---------+------+------------------------------------------------------------------------------------
1 | (0,1) | 40 | f | \x0000000001002800000000000000f03f000000000000f03f000000000000f03f000000000000f03f
2 | (0,2) | 40 | f | \x00000000020028000000000000000040000000000000004000000000000000400000000000000040
3 | (0,3) | 40 | f | \x00000000030028000000000000000840000000000000084000000000000008400000000000000840
4 | (0,4) | 40 | f | \x00000000040028000000000000001040000000000000104000000000000010400000000000001040
5 | (0,5) | 40 | f | \x00000000050028000000000000001440000000000000144000000000000014400000000000001440
(5 rows)
bill@bill=> SELECT * FROM gist_page_items_bytea(get_raw_page('test_gist_idx', 2)) LIMIT 5;
itemoffset | ctid | itemlen | dead | key_data
------------+--------+---------+------+------------------------------------------------------------------------------------
1 | (1,10) | 40 | f | \x000001000a0028000000000000e064400000000000e064400000000000e064400000000000e06440
2 | (1,11) | 40 | f | \x000001000b0028000000000000006540000000000000654000000000000065400000000000006540
3 | (1,12) | 40 | f | \x000001000c0028000000000000206540000000000020654000000000002065400000000000206540
4 | (1,13) | 40 | f | \x000001000d0028000000000000406540000000000040654000000000004065400000000000406540
5 | (1,14) | 40 | f | \x000001000e0028000000000000606540000000000060654000000000006065400000000000606540
(5 rows)
