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><H1
CLASS="SECT1"
><A
NAME="PGROWLOCKS"
>F.27. pgrowlocks</A
></H1
><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="AEN150909"
>F.27.1. 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 shown in <A
HREF="pgrowlocks.html#PGROWLOCKS-COLUMNS"
>Table F-21</A
>.
</P
><DIV
CLASS="TABLE"
><A
NAME="PGROWLOCKS-COLUMNS"
></A
><P
><B
>Table F-21. <CODE
CLASS="FUNCTION"
>pgrowlocks</CODE
> Output Columns</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><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 multitransaction</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>multi</TT
></TD
><TD
><TT
CLASS="TYPE"
>boolean</TT
></TD
><TD
>True if locker is a multitransaction</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 multitransaction)</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 multitransaction)</TD
></TR
></TBODY
></TABLE
></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="AEN150976"
>F.27.2. Sample Output</A
></H2
><PRE
CLASS="SCREEN"
>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="AEN150979"
>F.27.3. Author</A
></H2
><P
> Tatsuo Ishii
</P
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