diff --git a/perl-xCAT/xCAT/ExtTab.pm b/perl-xCAT/xCAT/ExtTab.pm
new file mode 100644
index 000000000..9b63afe09
--- /dev/null
+++ b/perl-xCAT/xCAT/ExtTab.pm
@@ -0,0 +1,113 @@
+#!/usr/bin/env perl
+# IBM(c) 2007 EPL license http://www.eclipse.org/legal/epl-v10.html
+#-------------------------------------------------------
+package xCAT::ExtTab;
+BEGIN
+{
+    $::XCATROOT = $ENV{'XCATROOT'} ? $ENV{'XCATROOT'} : -d '/opt/xcat' ? '/opt/xcat' : '/usr';
+}
+use lib "$::XCATROOT/lib/perl";
+
+use xCAT::MsgUtils;
+use File::Path;
+
+%ext_tabspec=(); 
+$ext_defspec=();
+
+
+# loads user defined table spec. They are stored under /opt/xcat/lib/perl/xCAT_schema directory
+my $path="$::XCATROOT/lib/perl/xCAT_schema";
+my @extSchema=glob($path."/*.pm");
+   # print "\nextSchema=@extSchema\n";
+
+foreach (@extSchema) {
+    /.*\/([^\/]*).pm$/;
+    my $file=$_;
+    my $modname = $1;
+    no strict 'refs';
+    eval {require($_)};
+    if ($@) { 
+	xCAT::MsgUtils->message('ES',"\n  Warning: The user defined database table schema file $file cannot be located or has compiling errors.\n"); 
+	next;
+    }   
+    if (${"xCAT_schema::" . "$modname" . "::"}{tabspec}) {
+	my %tabspec=%{${"xCAT_schema::" . "$modname" . "::"}{tabspec}};
+	foreach my $tabname (keys(%tabspec)) {
+	    $ext_tabspec{$tabname}=$tabspec{$tabname};
+	}
+    } else {
+	xCAT::MsgUtils->message('ES', "\n  Warning: Cannot find \%tabspec variable in the user defined database table schema file $file\n");
+    }
+   
+    #get the defspec from each file and merge them into %ext_defspec
+    if (${"xCAT_schema::" . "$modname" . "::"}{defspec}) {
+	my %defspec=%{${"xCAT_schema::" . "$modname" . "::"}{defspec}};
+	foreach my $objname (keys(%defspec)) {
+	    if (exists($defspec{$objname}->{'attrs'})) {
+		if (exists($ext_defspec{$objname})) {
+                    #print "insert\n";
+		    my @attr_new=@{$defspec{$objname}->{'attrs'}};
+		    my @attr=@{$ext_defspec{$objname}->{'attrs'}};
+		    my %tmp_hash=();
+		    foreach my $orig (@attr) {
+			my $attrname=$orig->{attr_name};
+			$tmp_hash{$attrname}=1;
+		    }
+		    foreach my $h (@attr_new) {
+			my $attrname=$h->{attr_name};
+			if (exists($tmp_hash{$attrname})) {
+			    xCAT::MsgUtils->message('ES', "\n  Warning: Conflict when adding user defined defspec from file $file. Attribute name $attrname is already defined in object $objname.  \n");
+			} else {
+			    #print "\ngot here objname=$objname, attrname=" . $h->{attr_name} . "\n";
+			    push(@{$ext_defspec{$objname}->{'attrs'}}, $h); 
+			}
+		    }
+		} else {
+		    #print "\ngot here objname=$objname, file=$file\n";
+		    $ext_defspec{$objname}=$defspec{$objname};
+		}	    
+	    }
+	}
+    }   
+    
+} #foreach  
+
+#print out the defspec
+#print "\nexternal defspec:\n";
+#foreach(%ext_defspec) {
+#    print "  $_:\n";
+#    my @attr=@{$ext_defspec{$_}->{'attrs'}};
+#    foreach my $h (@attr) {
+#	print "    " . $h->{attr_name} . "\n";
+#    }
+#}  
+
+#-------------------------------------------------------
+=head1 xCAT::ExtTab
+
+    Handles user defined database tables.
+
+=cut
+#------------------------------------------------------
+
+#-------------------------------------------------------
+
+=head3  updateTables
+
+     It is called by xcatd to generate the user-defined tables 
+  if they do not exist, it also updates the tables if there is 
+  Schmea change. 
+
+
+=cut
+#-------------------------------------------------------
+
+sub updateTables
+{
+    #print "\nupdateTables\n";
+    foreach (keys %ext_tabspec) {
+	my $table= xCAT::Table->new($_,-create=>1,-autocommit=>1);
+    }
+}
+
+1;
diff --git a/perl-xCAT/xCAT/Schema.pm b/perl-xCAT/xCAT/Schema.pm
index 4123945bc..7ed5c0c5c 100644
--- a/perl-xCAT/xCAT/Schema.pm
+++ b/perl-xCAT/xCAT/Schema.pm
@@ -1,5 +1,11 @@
 # IBM(c) 2007 EPL license http://www.eclipse.org/legal/epl-v10.html
 package xCAT::Schema;
+BEGIN
+{
+    $::XCATROOT = $ENV{'XCATROOT'} ? $ENV{'XCATROOT'} : -d '/opt/xcat' ? '/opt/xcat' : '/usr';
+}
+use lib "$::XCATROOT/lib/perl";
+use xCAT::ExtTab;
 
 # !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 #
@@ -578,6 +584,18 @@ performance => {
 );        # end of tabspec definition
 
 
+
+###################################################
+# adding user defined external tables
+##################################################
+foreach my $tabname (keys(%xCAT::ExtTab::ext_tabspec)) {
+    $tabspec{$tabname}=$xCAT::ExtTab::ext_tabspec{$tabname};
+}
+ 
+
+
+
+
 ####################################################
 #
 #  Data abstraction definitions
@@ -623,7 +641,7 @@ performance => {
 #site =>    { attrs => [], attrhash => {}, objkey => 'sitename' },
   policy => { attrs => [], attrhash => {}, objkey => 'priority' },
   monitoring => { attrs => [], attrhash => {}, objkey => 'name' },
-  notification => { attrs => [], attrhash => {}, objkey => 'filename' }
+  notification => { attrs => [], attrhash => {}, objkey => 'filename' },
 );
 
 
@@ -1410,28 +1428,46 @@ push(@{$defspec{group}->{'attrs'}}, @nodeattrs);
                  },
 );
 
-#########################
-#     performance table    #
-#########################
-@{$defspec{performance}->{'attrs'}} = (
 
-        {attr_name => 'timestamp',
-                 tabentry => 'performance.timestamp',
-                 access_tabentry => 'performance.timestamp=attr:timestamp',
-                 },
-        {attr_name => 'node',
-                 tabentry => 'performance.node',
-                 access_tabentry => 'performance.timestamp=attr:timestamp',
-  },
-        {attr_name => 'attrname',
-                 tabentry => 'performance.netname',
-                 access_tabentry => 'performance.timestamp=attr:timestamp',
-  },
-        {attr_name => 'attrvalue',
-                 tabentry => 'performance.attrvalue',
-                 access_tabentry => 'performance.timestamp=attr:timestamp',
-  },
-             );
+
+
+###################################################
+# adding user defined external defspec
+##################################################
+foreach my $objname (keys(%xCAT::ExtTab::ext_defspec)) {
+    if (exists($xCAT::ExtTab::ext_defspec{$objname}->{'attrs'})) {
+	if (exists($defspec{$objname})) {
+	    my @extattr=@{$xCAT::ExtTab::ext_defspec{$objname}->{'attrs'}};
+	    my @attr=@{$defspec{$objname}->{'attrs'}};
+	    my %tmp_hash=();
+	    foreach my $orig (@attr) {
+		my $attrname=$orig->{attr_name};
+		$tmp_hash{$attrname}=1;
+	    }
+	    foreach(@extattr) {
+		my $attrname=$_->{attr_name};
+		if (exists($tmp_hash{$attrname})) {
+		    xCAT::MsgUtils->message('ES', "\n  Warning: Conflict when adding user defined defspec. Attribute name $attrname is already defined in object $objname. \n");
+		} else {
+		    push(@{$defspec{$objname}->{'attrs'}}, $_); 
+		}
+	    }
+	} else {
+	    $defspec{$objname}=$xCAT::ExtTab::ext_defspec{$objname};
+	}
+    }
+}
+
+
+#print "\ndefspec:\n";
+#foreach(%xCAT::Schema::defspec) {
+#    print "  $_:\n";
+#    my @attr=@{$xCAT::Schema::defspec{$_}->{'attrs'}};
+#    foreach my $h (@attr) {
+#	print "    " . $h->{attr_name} . "\n";
+#    }
+#}  
+
 
 # Build a corresponding hash for the attribute names to make
 # definition access easier
diff --git a/xCAT-server/lib/xcat/schema/samples/Sample.pm b/xCAT-server/lib/xcat/schema/samples/Sample.pm
new file mode 100644
index 000000000..97601a18d
--- /dev/null
+++ b/xCAT-server/lib/xcat/schema/samples/Sample.pm
@@ -0,0 +1,91 @@
+# IBM(c) 2007 EPL license http://www.eclipse.org/legal/epl-v10.html
+package xCAT_schema::Sample;
+
+#################################################################################
+# This is a sample code that contains the user defined user database schema defination.
+# Here is a list of things you can do to add DB tables to xCAT database.
+#   1  copy this file to /opt/xcat/lib/perl/xCAT_schema directory, rename it.
+#   2  change the word Sample above to be the same as the file name.
+#   3  Do NOT change the variable name "%tabspec".
+#   4  lljob and llnode are the table names. 
+#      jobid, status, node, jobstatus are the column names. Change them to your like.
+#      Each table must have a 'disable' column.
+#   5 change the keys
+#   6 change the table descriptions and column descriptions to your like.
+#   7 restart the the xcatd, the tables will be automatically generated. 
+#   8 do above steps on all the service nodes. 
+# 
+###############################################################################
+%tabspec = (
+    lljob => {
+	cols => [qw(jobid status disable)],  #do not change 'disable, it is required by xCAT
+	keys => [qw(jobid)],
+	table_desc => 'Stores jobs.',
+	descriptions => {
+	    jobid => 'The job id.',
+	    status => 'The status of the job.',
+	    disable => "Set to 'yes' or '1' to comment out this row.",
+	},
+    },
+    llnode => {
+        cols => [qw(node jobid jobstatus disable)],
+        keys => [qw(node)],
+        table_desc => 'Stores the node status.',
+        descriptions => {
+            node=> 'The node.',
+            jobid => 'The job that runs on the node.',
+            jobstatus => 'The status of the job on the node.',
+	    disable => "Set to 'yes' or '1' to comment out this row.",
+        },
+    },
+); # end of tabspec definition
+
+
+
+
+
+
+
+##################################################################
+# The following %defspec is OPTIONAL. You only need to define it 
+# if you want your tables to work with xCAT object abstraction layer
+# commands such as lsdef, mkdef, chdef and rmdef.
+#
+# Note: The xCAT database accessting commands such as
+#       tabdump, chtab, gettab, nodels, nodeadd, nodech, etc. 
+#       still work without it.
+################################################################## 
+
+%defspec = (
+    job => { attrs => [], attrhash => {}, objkey => 'jobid' },   #create a new object called 'job', 
+);
+
+#define the attribtues in the 'job' object using the lljob talbe columns.
+@{$defspec{job}->{'attrs'}} = 
+(
+    {   attr_name => 'jobid',
+	tabentry => 'lljob.jobid',
+	access_tabentry => 'lljob.jobid=attr:jobid',
+    },
+    {   attr_name => 'status',
+	tabentry => 'lljob.status',
+	access_tabentry => 'lljob.jobid=attr:jobid',
+    },
+);
+
+#object 'node' already defined in /opt/xcat/lib/perl/xCAT/Schema.pm. 
+#Here we just add jobid and jobstatus attributes to the node object
+@{$defspec{node}->{'attrs'}} = 
+(
+    {	attr_name => 'jobid',
+	tabentry => 'llnode.jobid',
+	access_tabentry => 'llnode.node=attr:node',
+    },
+    {	attr_name => 'jobstatus',
+	tabentry => 'llnode.jobstatus',
+	access_tabentry => 'llnode.node=attr:node',
+    },
+);
+1;
+
+
diff --git a/xCAT-server/sbin/xcatd b/xCAT-server/sbin/xcatd
index eb6d8491b..998911f60 100755
--- a/xCAT-server/sbin/xcatd
+++ b/xCAT-server/sbin/xcatd
@@ -52,6 +52,7 @@ if ($^O =~ /^linux/i) {
 	$XML::Simple::PREFERRED_PARSER='XML::Parser';
 }
 use xCAT::Table;
+use xCAT::ExtTab;
 use Data::Dumper;
 use Getopt::Long;
 use Sys::Syslog qw(:DEFAULT setlogsock);
@@ -120,6 +121,14 @@ $SIG{PIPE} = sub {
     confess "SIGPIPE $$progname encountered a broken pipe (probably Ctrl-C by client)"
 };
 $progname = \$0;
+
+
+#create the user defined external database tables if they do not exist.
+#update the tables if there are schema changes.
+if (xCAT::Utils->isMN()) {
+    xCAT::ExtTab->updateTables();
+}
+
 sub daemonize {
   chdir('/');
   umask 0022;
diff --git a/xCAT-server/xCAT-server.spec b/xCAT-server/xCAT-server.spec
index e2528d3b0..cc80d154f 100644
--- a/xCAT-server/xCAT-server.spec
+++ b/xCAT-server/xCAT-server.spec
@@ -47,7 +47,7 @@ mkdir -p $RPM_BUILD_ROOT/%{prefix}/lib/perl/xCAT_plugin
 mkdir -p $RPM_BUILD_ROOT/opt/xcat/xdsh/Context
 mkdir -p $RPM_BUILD_ROOT/%{prefix}/lib/perl/xCAT_monitoring/samples
 mkdir -p $RPM_BUILD_ROOT/%{prefix}/lib/perl/xCAT_monitoring/pcp
-
+mkdir -p $RPM_BUILD_ROOT/%{prefix}/lib/perl/xCAT_schema/samples
 
 %ifos linux
 cp -a share/xcat/install/* $RPM_BUILD_ROOT/%{prefix}/share/xcat/install/
@@ -108,6 +108,14 @@ chmod 644 $RPM_BUILD_ROOT/%{prefix}/lib/perl/xCAT_monitoring/samples/*
 chmod 755 $RPM_BUILD_ROOT/%{prefix}/lib/perl/xCAT_monitoring/pcp
 chmod 644 $RPM_BUILD_ROOT/%{prefix}/lib/perl/xCAT_monitoring/pcp/*
 
+
+cp -r lib/xcat/schema/* $RPM_BUILD_ROOT/%{prefix}/lib/perl/xCAT_schema
+chmod 644 $RPM_BUILD_ROOT/%{prefix}/lib/perl/xCAT_schema/*
+
+chmod 755 $RPM_BUILD_ROOT/%{prefix}/lib/perl/xCAT_schema/samples
+chmod 644 $RPM_BUILD_ROOT/%{prefix}/lib/perl/xCAT_schema/samples/*
+
+
 cp lib/xcat/shfunctions $RPM_BUILD_ROOT/%{prefix}/lib
 chmod 644 $RPM_BUILD_ROOT/%{prefix}/lib/shfunctions
 mkdir -p $RPM_BUILD_ROOT/etc/init.d