<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!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> </p></dd></dl></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ltree.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="passwordcheck.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.21. ltree </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> F.23. passwordcheck</td></tr></table></div></body></html>