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F.17. pageinspect

The pageinspect module provides functions that allow you to inspect the contents of database pages at a low level, which is useful for debugging purposes. All of these functions may be used only by superusers.

F.17.1. Functions

get_raw_page(text, int) returns bytea

get_raw_page reads the specified block of the named table and returns a copy as a bytea value. This allows a single time-consistent copy of the block to be obtained.

page_header(bytea) returns record

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

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

test=# SELECT * FROM page_header(get_raw_page('pg_class', 0));
    lsn    | tli | 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 the PageHeaderData struct. See src/include/storage/bufpage.h for details.

heap_page_items(bytea) returns setof record

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 with get_raw_page should be passed as argument. For example:

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

See src/include/storage/itemid.h and src/include/access/htup.h for explanations of the fields returned.

bt_metap(text) returns record

bt_metap returns information about a btree index's metapage. For example:

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

bt_page_stats returns summary information about single pages of btree indexes. For example:

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

bt_page_items returns detailed information about all of the items on a btree 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
     
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