From 15ce2d2e4a3e9ae70801a5caa07579200a66b510 Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Thu, 20 Mar 2003 04:51:44 +0000
Subject: > I can see a couple possible downsides: (a) the library might have
 some > weird behavior across fork boundaries; (b) the additional memory space
 > that has to be duplicated into child processes will cost something per >
 child launch, even if the child never uses it.  But these are only >
 arguments that it might not *always* be a prudent thing to do, not that > we
 shouldn't give the DBA the tool to do it if he wants.  So fire away.

Here is a patch for the above, including a documentation update. It
creates a new GUC variable "preload_libraries", that accepts a list in
the form:

   preload_libraries = '$libdir/mylib1:initfunc,$libdir/mylib2'

If ":initfunc" is omitted or not found, no initialization function is
executed, but the library is still preloaded. If "$libdir/mylib" isn't
found, the postmaster refuses to start.

In my testing with PL/R, it reduces the first call to a PL/R function
(after connecting) from almost 2 seconds, down to about 8 ms.

Joe Conway
---
 doc/src/sgml/runtime.sgml | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

(limited to 'doc/src')

diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 408c81e2ee5..0f53895fdcd 100644
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -1,5 +1,5 @@
 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.171 2003/03/20 03:34:55 momjian Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.172 2003/03/20 04:51:44 momjian Exp $
 -->
 
 <Chapter Id="runtime">
@@ -1799,6 +1799,35 @@ dynamic_library_path = '/usr/local/lib/postgresql:/home/my_project/lib:$libdir'
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><varname>PRELOAD_LIBRARIES</varname> (<type>string</type>)</term>
+      <indexterm><primary>preload_libraries</></>
+      <listitem>
+       <para>
+        This variable specifies one or more shared libraries that are to be
+	preloaded at Postmaster start. An initialization function can also be
+	optionally specified by adding a colon followed by the name of the
+	initialization function after the library name. For example
+	<literal>'$libdir/mylib:init_mylib'</literal> would cause <literal>mylib</>
+    to be preloaded and <literal>init_mylib</> to be executed. If more than
+	one library is to be loaded, they must be delimited with a comma.
+       </para>
+
+       <para>
+        If <literal>mylib</> is not found, the postmaster will fail to start.
+	However, if <literal>init_mylib</> is not found, <literal>mylib</> will
+	still be preloaded without executing the initialization function.
+       </para>
+
+       <para>
+        By preloading a shared library (and initializing it if applicable),
+	the library startup time is avoided when the library is used later in a
+	specific backend. However there is a cost in terms of memory duplication
+	as every backend is forked, whether or not the library is used.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><varname>REGEX_FLAVOR</varname> (<type>string</type>)</term>
       <indexterm><primary>regular expressions</></>
-- 
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