From 661b3e79c431e771f5d8e9ca647cbf90fbd6baa2 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 10 Jun 2009 19:21:37 +0000
Subject: [PATCH] Add a warning about possible strange behavior of volatile
functions 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.
---
doc/src/sgml/ref/declare.sgml | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/doc/src/sgml/ref/declare.sgml b/doc/src/sgml/ref/declare.sgml
index 641971149ac..e93b4cf594d 100644
--- a/doc/src/sgml/ref/declare.sgml
+++ b/doc/src/sgml/ref/declare.sgml
@@ -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
--
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