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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>F.22. pageinspect</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="ltree.html" title="F.21. ltree" /><link rel="next" href="passwordcheck.html" title="F.23. passwordcheck" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.22. pageinspect</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="ltree.html" title="F.21. ltree">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="passwordcheck.html" title="F.23. passwordcheck">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PAGEINSPECT"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.22. pageinspect</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="pageinspect.html#id-1.11.7.31.4">F.22.1. General Functions</a></span></dt><dt><span class="sect2"><a href="pageinspect.html#id-1.11.7.31.5">F.22.2. B-tree Functions</a></span></dt><dt><span class="sect2"><a href="pageinspect.html#id-1.11.7.31.6">F.22.3. BRIN Functions</a></span></dt><dt><span class="sect2"><a href="pageinspect.html#id-1.11.7.31.7">F.22.4. GIN Functions</a></span></dt><dt><span class="sect2"><a href="pageinspect.html#id-1.11.7.31.8">F.22.5. Hash Functions</a></span></dt></dl></div><a id="id-1.11.7.31.2" class="indexterm"></a><p>
The <code class="filename">pageinspect</code> 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.
</p><div class="sect2" id="id-1.11.7.31.4"><div class="titlepage"><div><div><h3 class="title">F.22.1. General Functions</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">
<code class="function">get_raw_page(relname text, fork text, blkno int) returns bytea</code>
<a id="id-1.11.7.31.4.2.1.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">get_raw_page</code> reads the specified block of the named
relation and returns a copy as a <code class="type">bytea</code> value. This allows a
single time-consistent copy of the block to be obtained.
<em class="replaceable"><code>fork</code></em> should be <code class="literal">'main'</code> for
the main data fork, <code class="literal">'fsm'</code> for the free space map,
<code class="literal">'vm'</code> for the visibility map, or <code class="literal">'init'</code>
for the initialization fork.
</p></dd><dt><span class="term">
<code class="function">get_raw_page(relname text, blkno int) returns bytea</code>
</span></dt><dd><p>
A shorthand version of <code class="function">get_raw_page</code>, for reading
from the main fork. Equivalent to
<code class="literal">get_raw_page(relname, 'main', blkno)</code>
</p></dd><dt><span class="term">
<code class="function">page_header(page bytea) returns record</code>
<a id="id-1.11.7.31.4.2.3.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">page_header</code> shows fields that are common to all
<span class="productname">PostgreSQL</span> heap and index pages.
</p><p>
A page image obtained with <code class="function">get_raw_page</code> should be
passed as argument. For example:
</p><pre class="screen">
test=# SELECT * FROM page_header(get_raw_page('pg_class', 0));
lsn | checksum | flags | lower | upper | special | pagesize | version | prune_xid
-----------+----------+--------+-------+-------+---------+----------+---------+-----------
0/24A1B50 | 0 | 1 | 232 | 368 | 8192 | 8192 | 4 | 0
</pre><p>
The returned columns correspond to the fields in the
<code class="structname">PageHeaderData</code> struct.
See <code class="filename">src/include/storage/bufpage.h</code> for details.
</p><p>
The <code class="structfield">checksum</code> field is the checksum stored in
the page, which might be incorrect if the page is somehow corrupted. If
data checksums are not enabled for this instance, then the value stored
is meaningless.
</p></dd><dt><span class="term">
<code class="function">page_checksum(page bytea, blkno int4) returns smallint</code>
<a id="id-1.11.7.31.4.2.4.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">page_checksum</code> computes the checksum for the page, as if
it was located at the given block.
</p><p>
A page image obtained with <code class="function">get_raw_page</code> should be
passed as argument. For example:
</p><pre class="screen">
test=# SELECT page_checksum(get_raw_page('pg_class', 0), 0);
page_checksum
---------------
13443
</pre><p>
Note that the checksum depends on the block number, so matching block
numbers should be passed (except when doing esoteric debugging).
</p><p>
The checksum computed with this function can be compared with
the <code class="structfield">checksum</code> result field of the
function <code class="function">page_header</code>. If data checksums are
enabled for this instance, then the two values should be equal.
</p></dd><dt><span class="term">
<code class="function">heap_page_items(page bytea) returns setof record</code>
<a id="id-1.11.7.31.4.2.5.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">heap_page_items</code> shows all line pointers on a heap
page. For those line pointers that are in use, tuple headers as well
as tuple raw data 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.
</p><p>
A heap page image obtained with <code class="function">get_raw_page</code> should
be passed as argument. For example:
</p><pre class="screen">
test=# SELECT * FROM heap_page_items(get_raw_page('pg_class', 0));
</pre><p>
See <code class="filename">src/include/storage/itemid.h</code> and
<code class="filename">src/include/access/htup_details.h</code> for explanations of the fields
returned.
</p></dd><dt><span class="term">
<code class="function">tuple_data_split(rel_oid oid, t_data bytea, t_infomask integer, t_infomask2 integer, t_bits text [, do_detoast bool]) returns bytea[]</code>
<a id="id-1.11.7.31.4.2.6.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">tuple_data_split</code> splits tuple data into attributes
in the same way as backend internals.
</p><pre class="screen">
test=# SELECT tuple_data_split('pg_class'::regclass, t_data, t_infomask, t_infomask2, t_bits) FROM heap_page_items(get_raw_page('pg_class', 0));
</pre><p>
This function should be called with the same arguments as the return
attributes of <code class="function">heap_page_items</code>.
</p><p>
If <em class="parameter"><code>do_detoast</code></em> is <code class="literal">true</code>,
attribute that will be detoasted as needed. Default value is
<code class="literal">false</code>.
</p></dd><dt><span class="term">
<code class="function">heap_page_item_attrs(page bytea, rel_oid regclass [, do_detoast bool]) returns setof record</code>
<a id="id-1.11.7.31.4.2.7.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">heap_page_item_attrs</code> is equivalent to
<code class="function">heap_page_items</code> except that it returns
tuple raw data as an array of attributes that can optionally
be detoasted by <em class="parameter"><code>do_detoast</code></em> which is
<code class="literal">false</code> by default.
</p><p>
A heap page image obtained with <code class="function">get_raw_page</code> should
be passed as argument. For example:
</p><pre class="screen">
test=# SELECT * FROM heap_page_item_attrs(get_raw_page('pg_class', 0), 'pg_class'::regclass);
</pre><p>
</p></dd><dt><span class="term">
<code class="function">fsm_page_contents(page bytea) returns text</code>
<a id="id-1.11.7.31.4.2.8.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">fsm_page_contents</code> 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.
</p><p>
See <code class="filename">src/backend/storage/freespace/README</code> for more
information on the structure of an FSM page.
</p></dd></dl></div></div><div class="sect2" id="id-1.11.7.31.5"><div class="titlepage"><div><div><h3 class="title">F.22.2. B-tree Functions</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">
<code class="function">bt_metap(relname text) returns record</code>
<a id="id-1.11.7.31.5.2.1.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">bt_metap</code> returns information about a B-tree
index's metapage. For example:
</p><pre class="screen">
test=# SELECT * FROM bt_metap('pg_cast_oid_index');
-[ RECORD 1 ]-----------+-------
magic | 340322
version | 3
root | 1
level | 0
fastroot | 1
fastlevel | 0
oldest_xact | 582
last_cleanup_num_tuples | 1000
</pre><p>
</p></dd><dt><span class="term">
<code class="function">bt_page_stats(relname text, blkno int) returns record</code>
<a id="id-1.11.7.31.5.2.2.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">bt_page_stats</code> returns summary information about
single pages of B-tree indexes. For example:
</p><pre class="screen">
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
</pre><p>
</p></dd><dt><span class="term">
<code class="function">bt_page_items(relname text, blkno int) returns setof record</code>
<a id="id-1.11.7.31.5.2.3.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">bt_page_items</code> returns detailed information about
all of the items on a B-tree index page. For example:
</p><pre class="screen">
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
</pre><p>
In a B-tree leaf page, <code class="structfield">ctid</code> points to a heap tuple.
In an internal page, the block number part of <code class="structfield">ctid</code>
points to another page in the index itself, while the offset part
(the second number) is ignored and is usually 1.
</p><p>
Note that the first item on any non-rightmost page (any page with
a non-zero value in the <code class="structfield">btpo_next</code> field) is the
page's <span class="quote">“<span class="quote">high key</span>”</span>, meaning its <code class="structfield">data</code>
serves as an upper bound on all items appearing on the page, while
its <code class="structfield">ctid</code> field is meaningless. Also, on non-leaf
pages, the first real data item (the first item that is not a high
key) is a <span class="quote">“<span class="quote">minus infinity</span>”</span> item, with no actual value
in its <code class="structfield">data</code> field. Such an item does have a valid
downlink in its <code class="structfield">ctid</code> field, however.
</p></dd><dt><span class="term">
<code class="function">bt_page_items(page bytea) returns setof record</code>
<a id="id-1.11.7.31.5.2.4.1.2" class="indexterm"></a>
</span></dt><dd><p>
It is also possible to pass a page to <code class="function">bt_page_items</code>
as a <code class="type">bytea</code> value. A page image obtained
with <code class="function">get_raw_page</code> should be passed as argument. So
the last example could also be rewritten like this:
</p><pre class="screen">
test=# SELECT * FROM bt_page_items(get_raw_page('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
</pre><p>
All the other details are the same as explained in the previous item.
</p></dd></dl></div></div><div class="sect2" id="id-1.11.7.31.6"><div class="titlepage"><div><div><h3 class="title">F.22.3. BRIN Functions</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">
<code class="function">brin_page_type(page bytea) returns text</code>
<a id="id-1.11.7.31.6.2.1.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">brin_page_type</code> returns the page type of the given
<acronym class="acronym">BRIN</acronym> index page, or throws an error if the page is
not a valid <acronym class="acronym">BRIN</acronym> page. For example:
</p><pre class="screen">
test=# SELECT brin_page_type(get_raw_page('brinidx', 0));
brin_page_type
----------------
meta
</pre><p>
</p></dd><dt><span class="term">
<code class="function">brin_metapage_info(page bytea) returns record</code>
<a id="id-1.11.7.31.6.2.2.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">brin_metapage_info</code> returns assorted information
about a <acronym class="acronym">BRIN</acronym> index metapage. For example:
</p><pre class="screen">
test=# SELECT * FROM brin_metapage_info(get_raw_page('brinidx', 0));
magic | version | pagesperrange | lastrevmappage
------------+---------+---------------+----------------
0xA8109CFA | 1 | 4 | 2
</pre><p>
</p></dd><dt><span class="term">
<code class="function">brin_revmap_data(page bytea) returns setof tid</code>
<a id="id-1.11.7.31.6.2.3.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">brin_revmap_data</code> returns the list of tuple
identifiers in a <acronym class="acronym">BRIN</acronym> index range map page.
For example:
</p><pre class="screen">
test=# SELECT * FROM brin_revmap_data(get_raw_page('brinidx', 2)) LIMIT 5;
pages
---------
(6,137)
(6,138)
(6,139)
(6,140)
(6,141)
</pre><p>
</p></dd><dt><span class="term">
<code class="function">brin_page_items(page bytea, index oid) returns setof record</code>
<a id="id-1.11.7.31.6.2.4.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">brin_page_items</code> returns the data stored in the
<acronym class="acronym">BRIN</acronym> data page. For example:
</p><pre class="screen">
test=# SELECT * FROM brin_page_items(get_raw_page('brinidx', 5),
'brinidx')
ORDER BY blknum, attnum LIMIT 6;
itemoffset | blknum | attnum | allnulls | hasnulls | placeholder | value
------------+--------+--------+----------+----------+-------------+--------------
137 | 0 | 1 | t | f | f |
137 | 0 | 2 | f | f | f | {1 .. 88}
138 | 4 | 1 | t | f | f |
138 | 4 | 2 | f | f | f | {89 .. 176}
139 | 8 | 1 | t | f | f |
139 | 8 | 2 | f | f | f | {177 .. 264}
</pre><p>
The returned columns correspond to the fields in the
<code class="structname">BrinMemTuple</code> and <code class="structname">BrinValues</code> structs.
See <code class="filename">src/include/access/brin_tuple.h</code> for details.
</p></dd></dl></div></div><div class="sect2" id="id-1.11.7.31.7"><div class="titlepage"><div><div><h3 class="title">F.22.4. GIN Functions</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">
<code class="function">gin_metapage_info(page bytea) returns record</code>
<a id="id-1.11.7.31.7.2.1.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">gin_metapage_info</code> returns information about
a <acronym class="acronym">GIN</acronym> index metapage. For example:
</p><pre class="screen">
test=# SELECT * FROM gin_metapage_info(get_raw_page('gin_index', 0));
-[ RECORD 1 ]----+-----------
pending_head | 4294967295
pending_tail | 4294967295
tail_free_size | 0
n_pending_pages | 0
n_pending_tuples | 0
n_total_pages | 7
n_entry_pages | 6
n_data_pages | 0
n_entries | 693
version | 2
</pre><p>
</p></dd><dt><span class="term">
<code class="function">gin_page_opaque_info(page bytea) returns record</code>
<a id="id-1.11.7.31.7.2.2.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">gin_page_opaque_info</code> returns information about
a <acronym class="acronym">GIN</acronym> index opaque area, like the page type.
For example:
</p><pre class="screen">
test=# SELECT * FROM gin_page_opaque_info(get_raw_page('gin_index', 2));
rightlink | maxoff | flags
-----------+--------+------------------------
5 | 0 | {data,leaf,compressed}
(1 row)
</pre><p>
</p></dd><dt><span class="term">
<code class="function">gin_leafpage_items(page bytea) returns setof record</code>
<a id="id-1.11.7.31.7.2.3.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">gin_leafpage_items</code> returns information about
the data stored in a <acronym class="acronym">GIN</acronym> leaf page. For example:
</p><pre class="screen">
test=# SELECT first_tid, nbytes, tids[0:5] AS some_tids
FROM gin_leafpage_items(get_raw_page('gin_test_idx', 2));
first_tid | nbytes | some_tids
-----------+--------+----------------------------------------------------------
(8,41) | 244 | {"(8,41)","(8,43)","(8,44)","(8,45)","(8,46)"}
(10,45) | 248 | {"(10,45)","(10,46)","(10,47)","(10,48)","(10,49)"}
(12,52) | 248 | {"(12,52)","(12,53)","(12,54)","(12,55)","(12,56)"}
(14,59) | 320 | {"(14,59)","(14,60)","(14,61)","(14,62)","(14,63)"}
(167,16) | 376 | {"(167,16)","(167,17)","(167,18)","(167,19)","(167,20)"}
(170,30) | 376 | {"(170,30)","(170,31)","(170,32)","(170,33)","(170,34)"}
(173,44) | 197 | {"(173,44)","(173,45)","(173,46)","(173,47)","(173,48)"}
(7 rows)
</pre><p>
</p></dd></dl></div></div><div class="sect2" id="id-1.11.7.31.8"><div class="titlepage"><div><div><h3 class="title">F.22.5. Hash Functions</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">
<code class="function">hash_page_type(page bytea) returns text</code>
<a id="id-1.11.7.31.8.2.1.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">hash_page_type</code> returns page type of
the given <acronym class="acronym">HASH</acronym> index page. For example:
</p><pre class="screen">
test=# SELECT hash_page_type(get_raw_page('con_hash_index', 0));
hash_page_type
----------------
metapage
</pre><p>
</p></dd><dt><span class="term">
<code class="function">hash_page_stats(page bytea) returns setof record</code>
<a id="id-1.11.7.31.8.2.2.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">hash_page_stats</code> returns information about
a bucket or overflow page of a <acronym class="acronym">HASH</acronym> index.
For example:
</p><pre class="screen">
test=# SELECT * FROM hash_page_stats(get_raw_page('con_hash_index', 1));
-[ RECORD 1 ]---+-----------
live_items | 407
dead_items | 0
page_size | 8192
free_size | 8
hasho_prevblkno | 4096
hasho_nextblkno | 8474
hasho_bucket | 0
hasho_flag | 66
hasho_page_id | 65408
</pre><p>
</p></dd><dt><span class="term">
<code class="function">hash_page_items(page bytea) returns setof record</code>
<a id="id-1.11.7.31.8.2.3.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">hash_page_items</code> returns information about
the data stored in a bucket or overflow page of a <acronym class="acronym">HASH</acronym>
index page. For example:
</p><pre class="screen">
test=# SELECT * FROM hash_page_items(get_raw_page('con_hash_index', 1)) LIMIT 5;
itemoffset | ctid | data
------------+-----------+------------
1 | (899,77) | 1053474816
2 | (897,29) | 1053474816
3 | (894,207) | 1053474816
4 | (892,159) | 1053474816
5 | (890,111) | 1053474816
</pre><p>
</p></dd><dt><span class="term">
<code class="function">hash_bitmap_info(index oid, blkno int) returns record</code>
<a id="id-1.11.7.31.8.2.4.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">hash_bitmap_info</code> shows the status of a bit
in the bitmap page for a particular overflow page of <acronym class="acronym">HASH</acronym>
index. For example:
</p><pre class="screen">
test=# SELECT * FROM hash_bitmap_info('con_hash_index', 2052);
bitmapblkno | bitmapbit | bitstatus
-------------+-----------+-----------
65 | 3 | t
</pre><p>
</p></dd><dt><span class="term">
<code class="function">hash_metapage_info(page bytea) returns record</code>
<a id="id-1.11.7.31.8.2.5.1.2" class="indexterm"></a>
</span></dt><dd><p>
<code class="function">hash_metapage_info</code> returns information stored
in meta page of a <acronym class="acronym">HASH</acronym> index. For example:
</p><pre class="screen">
test=# SELECT magic, version, ntuples, ffactor, bsize, bmsize, bmshift,
test-# maxbucket, highmask, lowmask, ovflpoint, firstfree, nmaps, procid,
test-# regexp_replace(spares::text, '(,0)*}', '}') as spares,
test-# regexp_replace(mapp::text, '(,0)*}', '}') as mapp
test-# FROM hash_metapage_info(get_raw_page('con_hash_index', 0));
-[ RECORD 1 ]-------------------------------------------------------------------------------
magic | 105121344
version | 4
ntuples | 500500
ffactor | 40
bsize | 8152
bmsize | 4096
bmshift | 15
maxbucket | 12512
highmask | 16383
lowmask | 8191
ovflpoint | 28
firstfree | 1204
nmaps | 1
procid | 450
spares | {0,0,0,0,0,0,1,1,1,1,1,1,1,1,3,4,4,4,45,55,58,59,508,567,628,704,1193,1202,1204}
mapp | {65}
</pre><p>
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