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><H1
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><A
NAME="PGFREESPACEMAP"
>F.26. pg_freespacemap</A
></H1
><P
>  The <TT
CLASS="FILENAME"
>pg_freespacemap</TT
> module provides a means for examining the
  free space map (FSM). It provides a function called
  <CODE
CLASS="FUNCTION"
>pg_freespace</CODE
>, or two overloaded functions, to be
  precise. The functions show the value recorded in the free space map for
  a given page, or for all pages in the relation.
 </P
><P
>  By default public access is revoked from the functions, just in case
  there are security issues lurking.
 </P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN167671"
>F.26.1. Functions</A
></H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="FUNCTION"
>pg_freespace(rel regclass IN, blkno bigint IN) returns int2</CODE
>
     </DT
><DD
><P
>      Returns the amount of free space on the page of the relation, specified
      by <TT
CLASS="LITERAL"
>blkno</TT
>, according to the FSM.
     </P
></DD
><DT
><CODE
CLASS="FUNCTION"
>pg_freespace(rel regclass IN, blkno OUT bigint, avail OUT int2)</CODE
></DT
><DD
><P
>      Displays the amount of free space on each page of the relation,
      according to the FSM. A set of <TT
CLASS="LITERAL"
>(blkno bigint, avail int2)</TT
>
      tuples is returned, one tuple for each page in the relation.
     </P
></DD
></DL
></DIV
><P
>   The values stored in the free space map are not exact. They're rounded
   to precision of 1/256th of <TT
CLASS="SYMBOL"
>BLCKSZ</TT
> (32 bytes with default <TT
CLASS="SYMBOL"
>BLCKSZ</TT
>), and
   they're not kept fully up-to-date as tuples are inserted and updated.
  </P
><P
>   For indexes, what is tracked is entirely-unused pages, rather than free
   space within pages.  Therefore, the values are not meaningful, just
   whether a page is full or empty.
  </P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>    The interface was changed in version 8.4, to reflect the new FSM
    implementation introduced in the same version.
   </P
></BLOCKQUOTE
></DIV
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CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN167694"
>F.26.2. Sample Output</A
></H2
><PRE
CLASS="SCREEN"
>postgres=# SELECT * FROM pg_freespace('foo');
 blkno | avail 
-------+-------
     0 |     0
     1 |     0
     2 |     0
     3 |    32
     4 |   704
     5 |   704
     6 |   704
     7 |  1216
     8 |   704
     9 |   704
    10 |   704
    11 |   704
    12 |   704
    13 |   704
    14 |   704
    15 |   704
    16 |   704
    17 |   704
    18 |   704
    19 |  3648
(20 rows)

postgres=# SELECT * FROM pg_freespace('foo', 7);
 pg_freespace 
--------------
         1216
(1 row)</PRE
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><H2
CLASS="SECT2"
><A
NAME="AEN167697"
>F.26.3. Author</A
></H2
><P
>   Original version by Mark Kirkwood <CODE
CLASS="EMAIL"
>&#60;<A
HREF="mailto:markir@paradise.net.nz"
>markir@paradise.net.nz</A
>&#62;</CODE
>.
   Rewritten in version 8.4 to suit new FSM implementation by Heikki
   Linnakangas <CODE
CLASS="EMAIL"
>&#60;<A
HREF="mailto:heikki@enterprisedb.com"
>heikki@enterprisedb.com</A
>&#62;</CODE
>
  </P
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