~ubuntu-branches/ubuntu/trusty/postgresql-9.3/trusty-updates : contents of doc/src/sgml/html/pageinspect.html at revision 27

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><H1
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><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="AEN156092"
>F.22.1. Functions</A
></H2
><P
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><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 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"
>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>
     </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
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