<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >pageinspect</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 9.6.21 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Additional Supplied Modules" HREF="contrib.html"><LINK REL="PREVIOUS" TITLE="ltree" HREF="ltree.html"><LINK REL="NEXT" TITLE="passwordcheck" HREF="passwordcheck.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2021-02-27T18:26:08"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="4" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.6.21 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="ltree" HREF="ltree.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="contrib.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Appendix F. Additional Supplied Modules</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="passwordcheck" HREF="passwordcheck.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="PAGEINSPECT" >F.22. pageinspect</A ></H1 ><P > The <TT CLASS="FILENAME" >pageinspect</TT > 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" ><H2 CLASS="SECT2" ><A NAME="AEN140823" >F.22.1. Functions</A ></H2 ><P ></P ><DIV CLASS="VARIABLELIST" ><DL ><DT ><CODE CLASS="FUNCTION" >get_raw_page(relname text, fork text, blkno int) returns bytea</CODE > </DT ><DD ><P > <CODE CLASS="FUNCTION" >get_raw_page</CODE > reads the specified block of the named relation and returns a copy as a <TT CLASS="TYPE" >bytea</TT > value. This allows a single time-consistent copy of the block to be obtained. <TT CLASS="REPLACEABLE" ><I >fork</I ></TT > should be <TT CLASS="LITERAL" >'main'</TT > for the main data fork, <TT CLASS="LITERAL" >'fsm'</TT > for the free space map, <TT CLASS="LITERAL" >'vm'</TT > for the visibility map, or <TT CLASS="LITERAL" >'init'</TT > for the initialization fork. </P ></DD ><DT ><CODE CLASS="FUNCTION" >get_raw_page(relname text, blkno int) returns bytea</CODE ></DT ><DD ><P > A shorthand version of <CODE CLASS="FUNCTION" >get_raw_page</CODE >, for reading from the main fork. Equivalent to <TT CLASS="LITERAL" >get_raw_page(relname, 'main', blkno)</TT > </P ></DD ><DT ><CODE CLASS="FUNCTION" >page_header(page bytea) returns record</CODE > </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 | 1 | 1 | 232 | 368 | 8192 | 8192 | 4 | 0</PRE ><P> The returned columns correspond to the fields in the <TT CLASS="STRUCTNAME" >PageHeaderData</TT > struct. See <TT CLASS="FILENAME" >src/include/storage/bufpage.h</TT > for details. </P ></DD ><DT ><CODE CLASS="FUNCTION" >heap_page_items(page bytea) returns setof record</CODE > </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 <TT CLASS="FILENAME" >src/include/storage/itemid.h</TT > and <TT CLASS="FILENAME" >src/include/access/htup_details.h</TT > for explanations of the fields returned. </P ></DD ><DT ><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 > </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 <TT CLASS="PARAMETER" >do_detoast</TT > is <TT CLASS="LITERAL" >true</TT >, attribute that will be detoasted as needed. Default value is <TT CLASS="LITERAL" >false</TT >. </P ></DD ><DT ><CODE CLASS="FUNCTION" >heap_page_item_attrs(page bytea, rel_oid regclass [, do_detoast bool]) returns setof record</CODE > </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 <TT CLASS="PARAMETER" >do_detoast</TT > which is <TT CLASS="LITERAL" >false</TT > 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 ><CODE CLASS="FUNCTION" >bt_metap(relname text) returns record</CODE > </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 | 2 root | 1 level | 0 fastroot | 1 fastlevel | 0</PRE ><P> </P ></DD ><DT ><CODE CLASS="FUNCTION" >bt_page_stats(relname text, blkno int) returns record</CODE > </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 ><CODE CLASS="FUNCTION" >bt_page_items(relname text, blkno int) returns setof record</CODE > </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, <TT CLASS="STRUCTFIELD" >ctid</TT > points to a heap tuple. In an internal page, the block number part of <TT CLASS="STRUCTFIELD" >ctid</TT > 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 <TT CLASS="STRUCTFIELD" >btpo_next</TT > field) is the page's <SPAN CLASS="QUOTE" >"high key"</SPAN >, meaning its <TT CLASS="STRUCTFIELD" >data</TT > serves as an upper bound on all items appearing on the page, while its <TT CLASS="STRUCTFIELD" >ctid</TT > 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" >"minus infinity"</SPAN > item, with no actual value in its <TT CLASS="STRUCTFIELD" >data</TT > field. Such an item does have a valid downlink in its <TT CLASS="STRUCTFIELD" >ctid</TT > field, however. </P ></DD ><DT ><CODE CLASS="FUNCTION" >brin_page_type(page bytea) returns text</CODE > </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 ><CODE CLASS="FUNCTION" >brin_metapage_info(page bytea) returns record</CODE > </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 ><CODE CLASS="FUNCTION" >brin_revmap_data(page bytea) returns setof tid</CODE > </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 ><CODE CLASS="FUNCTION" >brin_page_items(page bytea, index oid) returns setof record</CODE > </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 <TT CLASS="STRUCTNAME" >BrinMemTuple</TT > and <TT CLASS="STRUCTNAME" >BrinValues</TT > structs. See <TT CLASS="FILENAME" >src/include/access/brin_tuple.h</TT > for details. </P ></DD ><DT ><CODE CLASS="FUNCTION" >gin_metapage_info(page bytea) returns record</CODE > </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 ><CODE CLASS="FUNCTION" >gin_page_opaque_info(page bytea) returns record</CODE > </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 ><CODE CLASS="FUNCTION" >gin_leafpage_items(page bytea) returns setof record</CODE > </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 ><DT ><CODE CLASS="FUNCTION" >fsm_page_contents(page bytea) returns text</CODE > </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 <TT CLASS="FILENAME" >src/backend/storage/freespace/README</TT > for more information on the structure of an FSM page. </P ></DD ></DL ></DIV ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="ltree.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="passwordcheck.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >ltree</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="contrib.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >passwordcheck</TD ></TR ></TABLE ></DIV ></BODY ></HTML >