1 files changed, 48 insertions, 13 deletions
diff --git a/system/doc/design_principles/appup_cookbook.xml b/system/doc/design_principles/appup_cookbook.xml
index bc61578953..798b23d847 100644
--- a/system/doc/design_principles/appup_cookbook.xml
+++ b/system/doc/design_principles/appup_cookbook.xml
@@ -4,7 +4,7 @@
 <chapter>
   <header>
     <copyright>
-      <year>2003</year><year>2009</year>
+      <year>2003</year><year>2011</year>
       <holder>Ericsson AB. All Rights Reserved.</holder>
     </copyright>
     <legalnotice>
@@ -603,25 +603,60 @@ code_change(_OldVsn, State, port) ->
   </section>
 
   <section>
-    <title>Emulator Restart</title>
-    <p>If the emulator can or should be restarted, the very simple
-      <c>.relup</c> file can be created manually:</p>
+    <title>Emulator Restart and Upgrade</title>
+    <p>There are two upgrade instructions that will restart the emulator:</p>
+    <taglist>
+      <tag><c>restart_new_emulator</c></tag>
+      <item>Intended for when erts, kernel, stdlib or sasl is
+        upgraded. It is automatically added when the relup file is
+        generated by <c>systools:make_relup/3,4</c>. It is executed
+        before all other upgrade instructions. See
+        <seealso marker="release_handling#restart_new_emulator_instr">Release
+        Handling</seealso> for more information about this
+        instruction.</item>
+      <tag><c>restart_emulator</c></tag>
+      <item>Used when a restart of the emulator is required after all
+        other upgrade instructions are executed. See
+        <seealso marker="release_handling#restart_emulator_instr">Release
+        Handling</seealso> for more information about this
+        instruction.</item>
+    </taglist>
+
+    <p>If an emulator restart is necessary and no upgrade instructions
+      are needed, i.e. if the restart itself is enough for the
+      upgraded applications to start running the new versions, a very
+      simple <c>.relup</c> file can be created manually:</p>
     <code type="none">
 {"B",
  [{"A",
    [],
-   [restart_new_emulator]}],
+   [restart_emulator]}],
  [{"A",
    [],
-   [restart_new_emulator]}]
+   [restart_emulator]}]
 }.</code>
-    <p>This way, the release handler framework with automatic packing
-      and unpacking of release packages, automatic path updates etc. can
-      be used without having to specify <c>.appup</c> files.</p>
-    <p>If some transformation of persistent data, for example database
-      contents, needs to be done before installing the new release
-      version, instructions for this can be added to the <c>.relup</c>
-      file as well.</p>
+    <p>In this case, the release handler framework with automatic
+      packing and unpacking of release packages, automatic path
+      updates etc. can be used without having to specify <c>.appup</c>
+      files.</p>
+  </section>
+
+  <section>
+    <title>Emulator Upgrade from pre OTP R15</title>
+    <p>From OTP R15, an emulator upgrade is performed by restarting
+    the emulator with new versions of the core applications
+    (<c>kernel</c>, <c>stdlib</c> and <c>sasl</c>) before loading code
+    and running upgrade instruction for other applications. For this
+    to work, the release to upgrade from must includes OTP R15 or
+    later. For the case where the release to upgrade from includes an
+    earlier emulator version, <c>systools:make_relup</c> will create a
+    backwards compatible relup file. This means that all upgrade
+    instructions will be executed before the emulator is
+    restarted. The new application code will therefore be loaded into
+    the old emulator. If the new code is compiled with the new
+    emulator, there might be cases where the beam format has changed
+    and beam files can not be loaded. To overcome this problem, the
+    new code should be compiled with the old emulator.</p>
   </section>
 </chapter>