database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-28 23:42:10 +03:00
Code Activity

Modify UPDATE/DELETE WHERE CURRENT OF to use the FOR UPDATE infrastructure to

Browse Source 
locate the target row, if the cursor was declared with FOR UPDATE or FOR
SHARE.  This approach is more flexible and reliable than digging through the
plan tree; for instance it can cope with join cursors.  But we still provide
the old code for use with non-FOR-UPDATE cursors.  Per gripe from Robert Haas.
This commit is contained in:
Tom Lane
2008-11-16 17:34:28 +00:00
parent 30f272a79b
commit 18004101ac
9 changed files with 246 additions and 70 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
doc/src/sgml/plpgsql.sgml
View File

@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.135 2008/10/28 22:02:05 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.136 2008/11/16 17:34:28 tgl Exp $ -->
<chapter id="plpgsql">
<title><application>PL/pgSQL</application> - <acronym>SQL</acronym> Procedural Language</title>
@ -2674,9 +2674,10 @@ DELETE FROM <replaceable>table</replaceable> WHERE CURRENT OF <replaceable>curso
<para>
When a cursor is positioned on a table row, that row can be updated
or deleted using the cursor to identify the row. Note that this
only works for simple (non-join, non-grouping) cursor queries.
For additional information see the
or deleted using the cursor to identify the row. There are
restrictions on what the cursor's query can be (in particular,
no grouping) and it's best to use <literal>FOR UPDATE</> in the
cursor. For additional information see the
<xref linkend="sql-declare" endterm="sql-declare-title">
reference page.
</para>

51
doc/src/sgml/ref/declare.sgml
View File

@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/declare.sgml,v 1.44 2008/11/14 10:22:46 petere Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/declare.sgml,v 1.45 2008/11/16 17:34:28 tgl Exp $
PostgreSQL documentation
-->
@ -213,6 +213,12 @@ DECLARE <replaceable class="parameter">name</replaceable> [ BINARY ] [ INSENSITI
specified, then backward fetches are disallowed in any case.
</para>
<para>
Backward fetches are also disallowed when the query
includes <literal>FOR UPDATE</> or <literal>FOR SHARE</>; therefore
<literal>SCROLL</literal> may not be specified in this case.
</para>
<para>
If the cursor's query includes <literal>FOR UPDATE</> or <literal>FOR
SHARE</>, then returned rows are locked at the time they are first
@ -221,19 +227,40 @@ DECLARE <replaceable class="parameter">name</replaceable> [ BINARY ] [ INSENSITI
these options.
In addition, the returned rows will be the most up-to-date versions;
therefore these options provide the equivalent of what the SQL standard
calls a <quote>sensitive cursor</>. It is often wise to use <literal>FOR
UPDATE</> if the cursor is intended to be used with <command>UPDATE
... WHERE CURRENT OF</> or <command>DELETE ... WHERE CURRENT OF</>,
since this will prevent other sessions from changing the rows between
the time they are fetched and the time they are updated. Without
<literal>FOR UPDATE</>, a subsequent <literal>WHERE CURRENT OF</> command
will have no effect if the row was changed meanwhile.
calls a <quote>sensitive cursor</>. (Specifying <literal>INSENSITIVE</>
together with <literal>FOR UPDATE</> or <literal>FOR SHARE</> is an error.)
</para>
<para>
<literal>SCROLL</literal> may not be specified when the query
includes <literal>FOR UPDATE</> or <literal>FOR SHARE</>.
</para>
<caution>
<para>
It is generally recommended to use <literal>FOR UPDATE</> if the cursor
is intended to be used with <command>UPDATE ... WHERE CURRENT OF</> or
<command>DELETE ... WHERE CURRENT OF</>. Using <literal>FOR UPDATE</>
prevents other sessions from changing the rows between the time they are
fetched and the time they are updated. Without <literal>FOR UPDATE</>,
a subsequent <literal>WHERE CURRENT OF</> command will have no effect if
the row was changed since the cursor was created.
</para>
<para>
Another reason to use <literal>FOR UPDATE</> is that without it, a
subsequent <literal>WHERE CURRENT OF</> might fail if the cursor query
does not meet the SQL standard's rules for being <quote>simply
updatable</> (in particular, the cursor must reference just one table
and not use grouping or <literal>ORDER BY</>). Cursors
that are not simply updatable might work, or might not, depending on plan
choice details; so in the worst case, an application might work in testing
and then fail in production.
</para>
<para>
The main reason not to use <literal>FOR UPDATE</> with <literal>WHERE
CURRENT OF</> is if you need the cursor to be scrollable, or to be
insensitive to the subsequent updates (that is, continue to show the old
data). If this is a requirement, pay close heed to the caveats shown
above.
</para>
</caution>
<para>
The SQL standard only makes provisions for cursors in embedded

15
doc/src/sgml/ref/delete.sgml
View File

@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/delete.sgml,v 1.34 2008/11/14 10:22:46 petere Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/delete.sgml,v 1.35 2008/11/16 17:34:28 tgl Exp $
PostgreSQL documentation
-->
@ -148,10 +148,13 @@ DELETE FROM [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ [ AS ]
<para>
The name of the cursor to use in a <literal>WHERE CURRENT OF</>
condition. The row to be deleted is the one most recently fetched
from this cursor. The cursor must be a simple (non-join, non-aggregate)
from this cursor. The cursor must be a non-grouping
query on the <command>DELETE</>'s target table.
Note that <literal>WHERE CURRENT OF</> cannot be
specified together with a Boolean condition.
specified together with a Boolean condition. See
<xref linkend="sql-declare" endterm="sql-declare-title">
for more information about using cursors with
<literal>WHERE CURRENT OF</>.
</para>
</listitem>
</varlistentry>
@ -244,14 +247,14 @@ DELETE FROM films WHERE kind &lt;&gt; 'Musical';
Clear the table <literal>films</literal>:
<programlisting>
DELETE FROM films;
</programlisting>
</programlisting>
</para>
<para>
Delete completed tasks, returning full details of the deleted rows:
<programlisting>
DELETE FROM tasks WHERE status = 'DONE' RETURNING *;
</programlisting>
</programlisting>
</para>
<para>
@ -259,7 +262,7 @@ DELETE FROM tasks WHERE status = 'DONE' RETURNING *;
<literal>c_tasks</> is currently positioned:
<programlisting>
DELETE FROM tasks WHERE CURRENT OF c_tasks;
</programlisting>
</programlisting>
</para>
</refsect1>

11
doc/src/sgml/ref/update.sgml
View File

@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.47 2008/11/14 10:22:47 petere Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.48 2008/11/16 17:34:28 tgl Exp $
PostgreSQL documentation
-->
@ -167,10 +167,13 @@ UPDATE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ [ AS ] <rep
<para>
The name of the cursor to use in a <literal>WHERE CURRENT OF</>
condition. The row to be updated is the one most recently fetched
from this cursor. The cursor must be a simple (non-join, non-aggregate)
from this cursor. The cursor must be a non-grouping
query on the <command>UPDATE</>'s target table.
Note that <literal>WHERE CURRENT OF</> cannot be
specified together with a Boolean condition.
specified together with a Boolean condition. See
<xref linkend="sql-declare" endterm="sql-declare-title">
for more information about using cursors with
<literal>WHERE CURRENT OF</>.
</para>
</listitem>
</varlistentry>
@ -331,7 +334,7 @@ COMMIT;
<literal>c_films</> is currently positioned:
<programlisting>
UPDATE films SET kind = 'Dramatic' WHERE CURRENT OF c_films;
</programlisting>
</programlisting>
</para>
</refsect1>