--- loncom/lonnet/perl/lonnet.pm	2018/04/29 00:53:23	1.1172.2.94
+++ loncom/lonnet/perl/lonnet.pm	2018/09/02 02:13:59	1.1172.2.95
@@ -1,7 +1,7 @@
 # The LearningOnline Network
 # TCP networking package
 #
-# $Id: lonnet.pm,v 1.1172.2.94 2018/04/29 00:53:23 raeburn Exp $
+# $Id: lonnet.pm,v 1.1172.2.95 2018/09/02 02:13:59 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -9652,13 +9652,25 @@ sub generate_coursenum {
 sub is_course {
     my ($cdom, $cnum) = scalar(@_) == 1 ? 
          ($_[0] =~ /^($match_domain)_($match_courseid)$/)  :  @_;
-
-    return unless $cdom and $cnum;
-
-    my %courses = &courseiddump($cdom, '.', 1, '.', '.', $cnum, undef, undef,
-        '.');
-
-    return unless(exists($courses{$cdom.'_'.$cnum}));
+    return unless (($cdom =~ /^$match_domain$/) && ($cnum =~ /^$match_courseid$/));
+    my $uhome=&homeserver($cnum,$cdom);
+    my $iscourse;
+    if (grep { $_ eq $uhome } current_machine_ids()) {
+        $iscourse = &LONCAPA::Lond::is_course($cdom,$cnum);
+    } else {
+        my $hashid = $cdom.':'.$cnum;
+        ($iscourse,my $cached) = &is_cached_new('iscourse',$hashid);
+        unless (defined($cached)) {
+            my %courses = &courseiddump($cdom, '.', 1, '.', '.',
+                                        $cnum,undef,undef,'.');
+            $iscourse = 0;
+            if (exists($courses{$cdom.'_'.$cnum})) {
+                $iscourse = 1;
+            }
+            &do_cache_new('iscourse',$hashid,$iscourse,3600);
+        }
+    }
+    return unless($iscourse);
     return wantarray ? ($cdom, $cnum) : $cdom.'_'.$cnum;
 }