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postgresql9.6-docs-9.6.22-1.mga7.noarch.rpm

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>Appendix F. Additional Supplied Modules</TD
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><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="AEN141007"
>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
>,
      attributes 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
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