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Add NOWAIT option to SELECT FOR UPDATE/SHARE.

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Original patch by Hans-Juergen Schoenig, revisions by Karel Zak
and Tom Lane.
This commit is contained in:
Tom Lane
2005-08-01 20:31:16 +00:00
parent ca7abcd89d
commit 2a4fad1a0e
28 changed files with 387 additions and 157 deletions
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31
doc/src/sgml/ref/select.sgml
View File

@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.88 2005/07/14 06:17:36 neilc Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.89 2005/08/01 20:31:04 tgl Exp $
PostgreSQL documentation
-->
@@ -30,7 +30,7 @@ SELECT [ ALL | DISTINCT [ ON ( <replaceable class="parameter">expression</replac
[ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [, ...] ]
[ LIMIT { <replaceable class="parameter">count</replaceable> | ALL } ]
[ OFFSET <replaceable class="parameter">start</replaceable> ]
[ FOR { UPDATE | SHARE } [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ] ]
[ FOR { UPDATE | SHARE } [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ] [ NOWAIT ] ]
where <replaceable class="parameter">from_item</replaceable> can be one of:
@@ -151,7 +151,7 @@ where <replaceable class="parameter">from_item</replaceable> can be one of:
</listitem>
</orderedlist>
</para>
<para>
You must have <literal>SELECT</literal> privilege on a table to
read its values. The use of <literal>FOR UPDATE</literal> or
@@ -506,7 +506,7 @@ HAVING <replaceable class="parameter">condition</replaceable>
<replaceable class="parameter">select_statement</replaceable> is
any <command>SELECT</command> statement without an <literal>ORDER
BY</>, <literal>LIMIT</>, <literal>FOR UPDATE</literal>, or
<literal>FOR SHARE</literal> clause.
<literal>FOR SHARE</literal> clause.
(<literal>ORDER BY</> and <literal>LIMIT</> can be attached to a
subexpression if it is enclosed in parentheses. Without
parentheses, these clauses will be taken to apply to the result of
@@ -803,14 +803,14 @@ OFFSET <replaceable class="parameter">start</replaceable>
<para>
The <literal>FOR UPDATE</literal> clause has this form:
<synopsis>
FOR UPDATE [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ]
FOR UPDATE [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ] [ NOWAIT ]
</synopsis>
</para>
<para>
The closely related <literal>FOR SHARE</literal> clause has this form:
<synopsis>
FOR SHARE [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ]
FOR SHARE [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ] [ NOWAIT ]
</synopsis>
</para>
@@ -831,6 +831,18 @@ FOR SHARE [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ]
linkend="mvcc">.
</para>
<para>
To prevent the operation from waiting for other transactions to commit,
use the <literal>NOWAIT</> option. <command>SELECT FOR UPDATE
NOWAIT</command> reports an error, rather than waiting, if a selected row
cannot be locked immediately. Note that <literal>NOWAIT</> applies only
to the row-level lock(s) &mdash; the required <literal>ROW SHARE</literal>
table-level lock is still taken in the ordinary way (see
<xref linkend="mvcc">). You can use the <literal>NOWAIT</> option of
<xref linkend="sql-lock" endterm="sql-lock-title">
if you need to acquire the table-level lock without waiting.
</para>
<para>
<literal>FOR SHARE</literal> behaves similarly, except that it
acquires a shared rather than exclusive lock on each retrieved
@@ -843,7 +855,8 @@ FOR SHARE [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ]
<para>
It is currently not allowed for a single <command>SELECT</command>
statement to include both <literal>FOR UPDATE</literal> and
<literal>FOR SHARE</literal>.
<literal>FOR SHARE</literal>, nor can different parts of the statement use
both <literal>NOWAIT</> and normal waiting mode.
</para>
<para>
@@ -861,8 +874,8 @@ FOR SHARE [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ]
</para>
<para>
It is possible for a <command>SELECT</> command using both
<literal>LIMIT</literal> and <literal>FOR UPDATE/SHARE</literal>
It is possible for a <command>SELECT</> command using both
<literal>LIMIT</literal> and <literal>FOR UPDATE/SHARE</literal>
clauses to return fewer rows than specified by <literal>LIMIT</literal>.
This is because <literal>LIMIT</> is applied first. The command
selects the specified number of rows,

4
doc/src/sgml/ref/select_into.sgml
View File

@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/select_into.sgml,v 1.35 2005/04/28 21:47:10 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/select_into.sgml,v 1.36 2005/08/01 20:31:04 tgl Exp $
PostgreSQL documentation
-->
@@ -31,7 +31,7 @@ SELECT [ ALL | DISTINCT [ ON ( <replaceable class="PARAMETER">expression</replac
[ ORDER BY <replaceable class="PARAMETER">expression</replaceable> [ ASC | DESC | USING <replaceable class="PARAMETER">operator</replaceable> ] [, ...] ]
[ LIMIT { <replaceable class="PARAMETER">count</replaceable> | ALL } ]
[ OFFSET <replaceable class="PARAMETER">start</replaceable> ]
[ FOR { UPDATE | SHARE } [ OF <replaceable class="PARAMETER">tablename</replaceable> [, ...] ] ]
[ FOR { UPDATE | SHARE } [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ] [ NOWAIT ] ]
</synopsis>
</refsynopsisdiv>

4
doc/src/sgml/sql.sgml
View File

@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/sql.sgml,v 1.37 2005/07/14 06:17:35 neilc Exp $
$PostgreSQL: pgsql/doc/src/sgml/sql.sgml,v 1.38 2005/08/01 20:31:05 tgl Exp $
-->
<chapter id="sql-intro">
@@ -865,7 +865,7 @@ SELECT [ ALL | DISTINCT [ ON ( <replaceable class="PARAMETER">expression</replac
[ ORDER BY <replaceable class="PARAMETER">expression</replaceable> [ ASC | DESC | USING <replaceable class="PARAMETER">operator</replaceable> ] [, ...] ]
[ LIMIT { <replaceable class="PARAMETER">count</replaceable> | ALL } ]
[ OFFSET <replaceable class="PARAMETER">start</replaceable> ]
[ FOR { UPDATE | SHARE } [ OF <replaceable class="PARAMETER">class_name</replaceable> [, ...] ] ]
[ FOR { UPDATE | SHARE } [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ] [ NOWAIT ] ]
</synopsis>
</para>