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Add a warning about possible strange behavior of volatile functions

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in cursors.  This has always been the case, but given the lack of user
complaints about it, I'm not going to bother back-patching this.
This commit is contained in:
Tom Lane 2009-06-10 19:21:37 +00:00
parent 61dd4185ff
commit 661b3e79c4
1 changed files with 15 additions and 1 deletions
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16
doc/src/sgml/ref/declare.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/declare.sgml,v 1.46 2009/04/10 17:56:21 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/declare.sgml,v 1.47 2009/06/10 19:21:37 tgl Exp $
PostgreSQL documentation
-->
@ -228,6 +228,20 @@ DECLARE <replaceable class="parameter">name</replaceable> [ BINARY ] [ INSENSITI
<literal>SCROLL</literal> may not be specified in this case.
</para>
<caution>
<para>
Scrollable and <literal>WITH HOLD</literal> cursors may give unexpected
results if they invoke any volatile functions (see <xref
linkend="xfunc-volatility">). When a previously fetched row is
re-fetched, the functions might be re-executed, perhaps leading to
results different from the first time. One workaround for such cases
is to declare the cursor <literal>WITH HOLD</literal> and commit the
transaction before reading any rows from it. This will force the
entire output of the cursor to be materialized in temporary storage,
so that volatile functions are executed exactly once for each row.
</para>
</caution>
<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