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><H1
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><A
NAME="PGROWLOCKS"
>F.22. pgrowlocks</A
></H1
><A
NAME="AEN103251"
></A
><P
>  The <TT
CLASS="FILENAME"
>pgrowlocks</TT
> module provides a function to show row
  locking information for a specified table.
 </P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN103255"
>F.22.1. Overview</A
></H2
><PRE
CLASS="SYNOPSIS"
>pgrowlocks(text) returns setof record
  </PRE
><P
>   The parameter is the name of a table.  The result is a set of records,
   with one row for each locked row within the table.  The output columns
   are:
  </P
><DIV
CLASS="TABLE"
><A
NAME="AEN103259"
></A
><P
><B
>Table F-25. <CODE
CLASS="FUNCTION"
>pgrowlocks</CODE
> output columns</B
></P
><TABLE
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><COL><COL><COL><THEAD
><TR
><TH
>Name</TH
><TH
>Type</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>locked_row</TT
></TD
><TD
><TT
CLASS="TYPE"
>tid</TT
></TD
><TD
>Tuple ID (TID) of locked row</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>lock_type</TT
></TD
><TD
><TT
CLASS="TYPE"
>text</TT
></TD
><TD
><TT
CLASS="LITERAL"
>Shared</TT
> for shared lock, or
             <TT
CLASS="LITERAL"
>Exclusive</TT
> for exclusive lock</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>locker</TT
></TD
><TD
><TT
CLASS="TYPE"
>xid</TT
></TD
><TD
>Transaction ID of locker, or multixact ID if multi-transaction</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>multi</TT
></TD
><TD
><TT
CLASS="TYPE"
>boolean</TT
></TD
><TD
>True if locker is a multi-transaction</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>xids</TT
></TD
><TD
><TT
CLASS="TYPE"
>xid[]</TT
></TD
><TD
>Transaction IDs of lockers (more than one if multi-transaction)</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>pids</TT
></TD
><TD
><TT
CLASS="TYPE"
>integer[]</TT
></TD
><TD
>Process IDs of locking backends (more than one if multi-transaction)</TD
></TR
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></DIV
><P
>   <CODE
CLASS="FUNCTION"
>pgrowlocks</CODE
> takes <TT
CLASS="LITERAL"
>AccessShareLock</TT
> for the
   target table and reads each row one by one to collect the row locking
   information.  This is not very speedy for a large table.  Note that:
  </P
><P
></P
><OL
TYPE="1"
><LI
><P
>    If the table as a whole is exclusive-locked by someone else,
    <CODE
CLASS="FUNCTION"
>pgrowlocks</CODE
> will be blocked.
    </P
></LI
><LI
><P
>     <CODE
CLASS="FUNCTION"
>pgrowlocks</CODE
> is not guaranteed to produce a
     self-consistent snapshot.  It is possible that a new row lock is taken,
     or an old lock is freed, during its execution.
    </P
></LI
></OL
><P
>   <CODE
CLASS="FUNCTION"
>pgrowlocks</CODE
> does not show the contents of locked
   rows. If you want to take a look at the row contents at the same time, you
   could do something like this:

  </P><PRE
CLASS="PROGRAMLISTING"
>SELECT * FROM accounts AS a, pgrowlocks('accounts') AS p
  WHERE p.locked_row = a.ctid;
  </PRE
><P>

   Be aware however that (as of <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 8.3) such a
   query will be very inefficient.
  </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN103321"
>F.22.2. Sample output</A
></H2
><PRE
CLASS="PROGRAMLISTING"
>test=# SELECT * FROM pgrowlocks('t1');
 locked_row | lock_type | locker | multi |   xids    |     pids
------------+-----------+--------+-------+-----------+---------------
      (0,1) | Shared    |     19 | t     | {804,805} | {29066,29068}
      (0,2) | Shared    |     19 | t     | {804,805} | {29066,29068}
      (0,3) | Exclusive |    804 | f     | {804}     | {29066}
      (0,4) | Exclusive |    804 | f     | {804}     | {29066}
(4 rows)
  </PRE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN103324"
>F.22.3. Author</A
></H2
><P
>   Tatsuo Ishii
  </P
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