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diff --git a/doc/src/sgml/pageinspect.sgml b/doc/src/sgml/pageinspect.sgml new file mode 100644 index 0000000000..3fe1edf378 --- /dev/null +++ b/doc/src/sgml/pageinspect.sgml @@ -0,0 +1,125 @@ + +<sect1 id="pageinspect"> + <title>pageinspect</title> + + <indexterm zone="pageinspect"> + <primary>pageinspect</primary> + </indexterm> + + <para> + The functions in this module allow you to inspect the contents of data pages + at a low level, for debugging purposes. + </para> + + <sect2> + <title>Functions included</title> + + <itemizedlist> + <listitem> + <para> + <literal>get_raw_page</literal> reads one block of the named table and returns a copy as a + bytea field. This allows a single time-consistent copy of the block to be + made. Use of this functions is restricted to superusers. + </para> + </listitem> + + <listitem> + <para> + <literal>page_header</literal> shows fields which are common to all PostgreSQL heap and index + pages. Use of this function is restricted to superusers. + </para> + <para> + A page image obtained with <literal>get_raw_page</literal> should be passed as argument: + </para> + <programlisting> + test=# SELECT * FROM page_header(get_raw_page('pg_class',0)); + lsn | tli | flags | lower | upper | special | pagesize | version + ----------+-----+-------+-------+-------+---------+----------+--------- + 0/3C5614 | 1 | 1 | 216 | 256 | 8192 | 8192 | 4 + (1 row) + </programlisting> + <para> + The returned columns correspond to the fields in the PageHeaderData-struct, + see src/include/storage/bufpage.h for more details. + </para> + </listitem> + + <listitem> + <para> + <literal>heap_page_items</literal> 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. Use of this function is restricted to + superusers. + </para> + <para> + A heap page image obtained with <literal>get_raw_page</literal> should be passed as argument: + </para> + <programlisting> + test=# SELECT * FROM heap_page_items(get_raw_page('pg_class',0)); + </programlisting> + <para> + See src/include/storage/itemid.h and src/include/access/htup.h for + explanations of the fields returned. + </para> + </listitem> + + <listitem> + <para> + <literal>bt_metap()</literal> returns information about the btree index metapage: + </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> + + <listitem> + <para> + <literal>bt_page_stats()</literal> shows information about single btree pages: + </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> + + <listitem> + <para> + <literal>bt_page_items()</literal> returns information about specific items on btree pages: + </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> + </itemizedlist> + </sect2> +</sect1> + |