get_raw_page reads the specified block of the named relation and returns a copy as abytea value. This allows a single time-consistent copy of the block to be obtained.fork should be'main' for the main data fork,'fsm' for the free space map,'vm' for the visibility map, or'init' for the initialization fork.

A shorthand version ofget_raw_page, for reading from the main fork. Equivalent toget_raw_page(relname, 'main', blkno)

page_header shows fields that are common to allPostgreSQL heap and index pages.

A page image obtained withget_raw_page should be passed as argument. For example:

test=# SELECT * FROM page_header(get_raw_page('pg_class', 0));    lsn    | checksum | flags  | lower | upper | special | pagesize | version | prune_xid-----------+----------+--------+-------+-------+---------+----------+---------+----------- 0/24A1B50 |        1 |      1 |   232 |   368 |    8192 |     8192 |       4 |         0

The returned columns correspond to the fields in thePageHeaderData struct. Seesrc/include/storage/bufpage.h for details.

heap_page_items shows all line pointers on a heap page. For those line pointers that are in use, tuple headers are also shown. All tuples are shown, whether or not the tuples were visible to an MVCC snapshot at the time the raw page was copied.

A heap page image obtained withget_raw_page should be passed as argument. For example:

test=# SELECT * FROM heap_page_items(get_raw_page('pg_class', 0));

Seesrc/include/storage/itemid.h andsrc/include/access/htup_details.h for explanations of the fields returned.

bt_metap returns information about a B-tree index's metapage. For example:

test=# SELECT * FROM bt_metap('pg_cast_oid_index');-[ RECORD 1 ]-----magic     | 340322version   | 2root      | 1level     | 0fastroot  | 1fastlevel | 0

bt_page_stats returns summary information about single pages of B-tree indexes. For example:

test=# SELECT * FROM bt_page_stats('pg_cast_oid_index', 1);-[ RECORD 1 ]-+-----blkno         | 1type          | llive_items    | 256dead_items    | 0avg_item_size | 12page_size     | 8192free_size     | 4056btpo_prev     | 0btpo_next     | 0btpo          | 0btpo_flags    | 3

bt_page_items returns detailed information about all of the items on a B-tree index page. For example:

test=# SELECT * FROM bt_page_items('pg_cast_oid_index', 1); itemoffset |  ctid   | itemlen | nulls | vars |    data------------+---------+---------+-------+------+-------------          1 | (0,1)   |      12 | f     | f    | 23 27 00 00          2 | (0,2)   |      12 | f     | f    | 24 27 00 00          3 | (0,3)   |      12 | f     | f    | 25 27 00 00          4 | (0,4)   |      12 | f     | f    | 26 27 00 00          5 | (0,5)   |      12 | f     | f    | 27 27 00 00          6 | (0,6)   |      12 | f     | f    | 28 27 00 00          7 | (0,7)   |      12 | f     | f    | 29 27 00 00          8 | (0,8)   |      12 | f     | f    | 2a 27 00 00

fsm_page_contents shows the internal node structure of a FSM page. The output is a multiline string, with one line per node in the binary tree within the page. Only those nodes that are not zero are printed. The so-called "next" pointer, which points to the next slot to be returned from the page, is also printed.

Seesrc/backend/storage/freespace/README for more information on the structure of an FSM page.