Add a new system view, pg_cursors, that displays the currently available

cursors. Patch from Joachim Wieland, review and ediorialization by Neil
Conway. The view lists cursors defined by DECLARE CURSOR, using SPI, or
via the Bind message of the frontend/backend protocol. This means the
view does not list the unnamed portal or the portal created to implement
EXECUTE. Because we do list SPI portals, there might be more rows in
this view than you might expect if you are using SPI implicitly (e.g.
via a procedural language).

Per recent discussion on -hackers, the query string included in the
view for cursors defined by DECLARE CURSOR is based on
debug_query_string. That means it is not accurate if multiple queries
separated by semicolons are submitted as one query string. However,
there doesn't seem a trivial fix for that: debug_query_string
is better than nothing. I also changed SPI_cursor_open() to include
the source text for the portal it creates: AFAICS there is no reason
not to do this.

Update the documentation and regression tests, bump the catversion.

4 files changed, 145 insertions, 5 deletions

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index c346005bd96..aee68c2f893 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -1,6 +1,6 @@
 <!--
  Documentation of the system catalogs, directed toward PostgreSQL developers
- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.117 2006/01/16 18:15:30 neilc Exp $
+ $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.118 2006/01/18 06:49:25 neilc Exp $
  -->
 
 <chapter id="catalogs">
@@ -4360,6 +4360,11 @@
 
     <tbody>
      <row>
+      <entry><link linkend="view-pg-cursors"><structname>pg_cursors</structname></link></entry>
+      <entry>open cursors</entry>
+     </row>
+
+     <row>
       <entry><link linkend="view-pg-group"><structname>pg_group</structname></link></entry>
       <entry>groups of database users</entry>
      </row>
@@ -4429,6 +4434,131 @@
   </table>
  </sect1>
 
+ <sect1 id="view-pg-cursors">
+  <title><structname>pg_cursors</structname></title>
+
+  <indexterm zone="view-pg-cursors">
+   <primary>pg_cursors</primary>
+  </indexterm>
+
+  <para>
+   The <structname>pg_cursors</structname> view lists the cursors that
+   are currently available. Cursors can be defined in several ways:
+   <itemizedlist>
+    <listitem>
+     <para>
+      via the <xref linkend="sql-declare" endterm="sql-declare-title">
+      statement in SQL
+     </para>
+    </listitem>
+
+    <listitem>
+     <para>
+      via the Bind message in the frontend/backend protocol, as
+      described in <xref linkend="protocol-flow-ext-query">
+     </para>
+    </listitem>
+
+    <listitem>
+     <para>
+      via the Server Programming Interface (SPI), as described in
+      <xref linkend="spi-interface">
+   </itemizedlist>
+
+   The <structname>pg_cursors</structname> view displays cursors
+   created by any of these means. Cursors only exist for the duration
+   of the transaction that defines them, unless they have been
+   declared <literal>WITH HOLD</literal>. Therefore non-holdable
+   cursors are only present in the view until the end of their
+   creating transaction.
+
+   <note>
+    <para>
+     Cursors are used internally to implement some of the components
+     of <productname>PostgreSQL</>, such as procedural languages.
+     Therefore, the <structname>pg_cursors</> view may include cursors
+     that have not been explicitly created by the user.
+    </para>
+   </note>
+  </para>
+
+  <table>
+   <title><structname>pg_cursors</> Columns</title>
+
+   <tgroup cols=4>
+    <thead>
+     <row>
+      <entry>Name</entry>
+      <entry>Type</entry>
+      <entry>References</entry>
+      <entry>Description</entry>
+     </row>
+    </thead>
+
+    <tbody>
+     <row>
+      <entry><structfield>name</structfield></entry>
+      <entry><type>text</type></entry>
+      <entry></entry>
+      <entry>The name of the cursor</entry>
+     </row>
+
+     <row>
+      <entry><structfield>statement</structfield></entry>
+      <entry><type>text</type></entry>
+      <entry></entry>
+      <entry>The verbatim query string submitted to declare this cursor</entry>
+     </row>
+
+     <row>
+      <entry><structfield>is_holdable</structfield></entry>
+      <entry><type>boolean</type></entry>
+      <entry></entry>
+      <entry>
+       <literal>true</literal> if the cursor is holdable (that is, it
+       can be accessed after the transaction that declared the cursor
+       has committed); <literal>false</literal> otherwise
+       </entry>
+     </row>
+
+     <row>
+      <entry><structfield>is_binary</structfield></entry>
+      <entry><type>boolean</type></entry>
+      <entry></entry>
+      <entry>
+       <literal>true</literal> if the cursor was declared
+       <literal>BINARY</literal>; <literal>false</literal>
+       otherwise
+       </entry>
+     </row>
+
+     <row>
+      <entry><structfield>is_scrollable</structfield></entry>
+      <entry><type>boolean</type></entry>
+      <entry></entry>
+      <entry>
+       <literal>true</> if the cursor is scrollable (that is, it
+       allows rows to be retrieved in a nonsequential manner);
+       <literal>false</literal> otherwise
+       </entry>
+     </row>
+
+     <row>
+      <entry><structfield>creation_time</structfield></entry>
+      <entry><type>timestamptz</type></entry>
+      <entry></entry>
+      <entry>The time at which the cursor was declared</entry>
+     </row>
+    </tbody>
+   </tgroup>
+  </table>
+
+  <para>
+   The <structname>pg_cursors</structname> view is read only.
+  </para>
+
+ </sect1>
+
  <sect1 id="view-pg-group">
   <title><structname>pg_group</structname></title>
 
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 07c9c642c75..689460ed92f 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/protocol.sgml,v 1.62 2005/08/14 22:19:49 petere Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/protocol.sgml,v 1.63 2006/01/18 06:49:25 neilc Exp $ -->
 
 <chapter id="protocol">
  <title>Frontend/Backend Protocol</title>
@@ -602,7 +602,7 @@
    </para>
   </sect2>
 
-  <sect2>
+  <sect2 id="protocol-flow-ext-query">
    <title>Extended Query</title>
 
    <para>
diff --git a/doc/src/sgml/ref/close.sgml b/doc/src/sgml/ref/close.sgml
index 3376476e26d..35f0993e6a2 100644
--- a/doc/src/sgml/ref/close.sgml
+++ b/doc/src/sgml/ref/close.sgml
@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/close.sgml,v 1.22 2005/01/04 00:39:53 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/close.sgml,v 1.23 2006/01/18 06:49:26 neilc Exp $
 PostgreSQL documentation
 -->
 
@@ -76,6 +76,11 @@ CLOSE <replaceable class="PARAMETER">name</replaceable>
    <xref linkend="sql-declare" endterm="sql-declare-title">
    statement to declare a cursor.
   </para>
+
+  <para>
+   You can see all available cursors by querying the
+   <structname>pg_cursors</structname> system view.
+  </para>
  </refsect1>
 
  <refsect1>
diff --git a/doc/src/sgml/ref/declare.sgml b/doc/src/sgml/ref/declare.sgml
index 0263145927d..f43e08f970d 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 1.33 2005/01/04 00:39:53 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/declare.sgml,v 1.34 2006/01/18 06:49:26 neilc Exp $
 PostgreSQL documentation
 -->
 
@@ -253,6 +253,11 @@ DECLARE <replaceable class="parameter">name</replaceable> [ BINARY ] [ INSENSITI
     the standard SQL cursor conventions, including those involving
     <command>DECLARE</command> and <command>OPEN</command> statements.
    </para>
+
+   <para>
+    You can see all available cursors by querying the
+    <structname>pg_cursors</structname> system view.
+   </para>
  </refsect1>
 
  <refsect1>