mirror of
https://github.com/postgres/postgres.git
synced 2025-12-19 17:02:53 +03:00
5f853c6556
relation forks. While the file names are not visible to users, for those that do peek into the data directory, it's nice to have more descriptive names. Per Greg Stark's suggestion.
206 lines
6.1 KiB
Plaintext
206 lines
6.1 KiB
Plaintext
<!-- $PostgreSQL: pgsql/doc/src/sgml/pageinspect.sgml,v 1.5 2008/10/06 14:13:17 heikki Exp $ -->
|
|
|
|
<sect1 id="pageinspect">
|
|
<title>pageinspect</title>
|
|
|
|
<indexterm zone="pageinspect">
|
|
<primary>pageinspect</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
The <filename>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.
|
|
</para>
|
|
|
|
<sect2>
|
|
<title>Functions</title>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>
|
|
<function>get_raw_page(relname text, fork text, blkno int) returns bytea</function>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
<function>get_raw_page</function> reads the specified block of the named
|
|
table and returns a copy as a <type>bytea</> value. This allows a
|
|
single time-consistent copy of the block to be obtained.
|
|
<literal>fork</literal> should be <literal>'main'</literal> for the main
|
|
data fork, or <literal>'fsm'</literal> for the FSM.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<function>get_raw_page(relname text, blkno int) returns bytea</function>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
A shorthand of above, for reading from the main fork. Equal to
|
|
<literal>get_raw_page(relname, 0, blkno)</literal>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<function>page_header(page bytea) returns record</function>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
<function>page_header</function> shows fields that are common to all
|
|
<productname>PostgreSQL</> heap and index pages.
|
|
</para>
|
|
|
|
<para>
|
|
A page image obtained with <function>get_raw_page</function> should be
|
|
passed as argument. For example:
|
|
</para>
|
|
<programlisting>
|
|
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
|
|
</programlisting>
|
|
|
|
<para>
|
|
The returned columns correspond to the fields in the
|
|
<structname>PageHeaderData</> struct.
|
|
See <filename>src/include/storage/bufpage.h</> for details.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<function>heap_page_items(page bytea) returns setof record</function>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
<function>heap_page_items</function> 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.
|
|
</para>
|
|
<para>
|
|
A heap page image obtained with <function>get_raw_page</function> should
|
|
be passed as argument. For example:
|
|
</para>
|
|
<programlisting>
|
|
test=# SELECT * FROM heap_page_items(get_raw_page('pg_class', 0));
|
|
</programlisting>
|
|
<para>
|
|
See <filename>src/include/storage/itemid.h</> and
|
|
<filename>src/include/access/htup.h</> for explanations of the fields
|
|
returned.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<function>bt_metap(relname text) returns record</function>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
<function>bt_metap</function> returns information about a btree
|
|
index's metapage. For example:
|
|
</para>
|
|
<programlisting>
|
|
test=# SELECT * FROM bt_metap('pg_cast_oid_index');
|
|
-[ RECORD 1 ]-----
|
|
magic | 340322
|
|
version | 2
|
|
root | 1
|
|
level | 0
|
|
fastroot | 1
|
|
fastlevel | 0
|
|
</programlisting>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<function>bt_page_stats(relname text, blkno int) returns record</function>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
<function>bt_page_stats</function> returns summary information about
|
|
single pages of btree indexes. For example:
|
|
</para>
|
|
<programlisting>
|
|
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
|
|
</programlisting>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<function>bt_page_items(relname text, blkno int) returns setof record</function>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
<function>bt_page_items</function> returns detailed information about
|
|
all of the items on a btree index page. For example:
|
|
</para>
|
|
<programlisting>
|
|
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
|
|
</programlisting>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<function>fsm_page_contents(page bytea) returns text</function>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
<function>fsm_page_contents</function> shows the internal node structure
|
|
of a FSM page. The output is a multi-line 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.
|
|
</para>
|
|
<para>
|
|
See <filename>src/backend/storage/freespace/README</> for more
|
|
information on the structure of an FSM page.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</sect2>
|
|
|
|
</sect1>
|