PostgreSQL 9.3.25 Documentation | ||||
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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.
get_raw_page(relname text, fork text,
blkno int) returns bytea
get_raw_page
reads the specified
block of the named relation and returns a copy as a bytea 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.
get_raw_page(relname text, blkno int)
returns bytea
A shorthand version of get_raw_page
, for reading from the main fork.
Equivalent to get_raw_page(relname, 'main',
blkno)
page_header(page 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 | 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 the PageHeaderData struct. See src/include/storage/bufpage.h for details.
heap_page_items(page 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_details.h for explanations of the fields returned.
bt_metap(relname text) returns
record
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 | 340322 version | 2 root | 1 level | 0 fastroot | 1 fastlevel | 0
bt_page_stats(relname text, blkno int)
returns record
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 | 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(relname text, blkno int)
returns setof record
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(page bytea) returns
text
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.
See src/backend/storage/freespace/README for more information on the structure of an FSM page.