PostgreSQL 8.3.23 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(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