Index: openacs-4/packages/acs-developer-support/tcl/acs-developer-support-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-developer-support/tcl/acs-developer-support-procs.tcl,v
diff -u -N -r1.55.2.3 -r1.55.2.4
--- openacs-4/packages/acs-developer-support/tcl/acs-developer-support-procs.tcl	16 Sep 2015 09:18:55 -0000	1.55.2.3
+++ openacs-4/packages/acs-developer-support/tcl/acs-developer-support-procs.tcl	27 Nov 2015 10:26:58 -0000	1.55.2.4
@@ -55,10 +55,20 @@
  ad_proc -public ds_enabled_p {} { 
      Returns true if developer-support facilities are enabled.
  } {
+     #
+     # On busy sites, frequent calls to [ds_enabled_p] leads to huge
+     # number of mutex locks for the nsv ds_properties. Therefore,
+     # cache its results in a per-thead variable.
+     #
+     if {[info exists ::__ds_enabled_p]} {
+         return $::ds_enabled_p
+     }
      if { ![nsv_exists ds_properties enabled_p] || ![nsv_get ds_properties enabled_p] } {
-         return 0
+         set ::ds_enabled_p 0
+     } else {
+         set ::ds_enabled_p 1
      }
-     return 1
+     return $::ds_enabled_p
  }
 
  ad_proc -public ds_collection_enabled_p {} {
@@ -359,8 +369,7 @@
  ad_proc -private ds_add { name args } { 
      Sets a developer-support property for the current request. 
  } {
-
-     if { [ds_enabled_p] && [ds_collection_enabled_p] } { 
+     if { [ds_enabled_p] && [ds_collection_enabled_p] } {
          if { [catch { nsv_exists ds_request . }] } {
              ns_log "Warning" "ds_request NSVs not initialized"
              return
@@ -692,7 +701,6 @@
 	# variables, which are deleted automatically after every
 	# request.
 	#
-	set ::ds_enabled_p 1
 	if {[::ds_collection_enabled_p] } {set ::ds_collection_enabled_p 1}
 	if {[::ds_profiling_enabled_p] } {set ::ds_profiling_enabled_p 1}
 	if {[::ds_show_p]} {set ::ds_show_p 1}
Index: openacs-4/packages/acs-developer-support/www/set.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-developer-support/www/set.tcl,v
diff -u -N -r1.3.2.1 -r1.3.2.2
--- openacs-4/packages/acs-developer-support/www/set.tcl	10 Sep 2015 08:21:24 -0000	1.3.2.1
+++ openacs-4/packages/acs-developer-support/www/set.tcl	27 Nov 2015 10:26:59 -0000	1.3.2.2
@@ -28,6 +28,7 @@
     }
     ds {
         nsv_set ds_properties enabled_p $enabled_p
+        set ::ds_enabled_p $enabled_p
     }
     frag {
         nsv_set ds_properties page_fragment_cache_p $enabled_p