track active search requests

src/dreyfus/priv/stats_descriptions.cfg

diff --git a/src/dreyfus/priv/stats_descriptions.cfg b/src/dreyfus/priv/stats_descriptions.cfg
index 7f93ee2..8183a4f 100644
--- a/src/dreyfus/priv/stats_descriptions.cfg
+++ b/src/dreyfus/priv/stats_descriptions.cfg
@@ -63,3 +63,8 @@
     {type, counter},
     {desc, <<"Search IO directly triggered by client requests">>}
 ]}.
+
+{[dreyfus, active_searches], [
+    {type, counter},
+    {desc, <<"number of active search requests">>}
+]}.
\ No newline at end of file

src/dreyfus/src/dreyfus_httpd.erl

diff --git a/src/dreyfus/src/dreyfus_httpd.erl b/src/dreyfus/src/dreyfus_httpd.erl
index f6607d6..3bf2522 100644
--- a/src/dreyfus/src/dreyfus_httpd.erl
+++ b/src/dreyfus/src/dreyfus_httpd.erl
@@ -31,7 +31,12 @@
 ]).
 
 handle_search_req(Req, Db, DDoc) ->
-    handle_search_req(Req, Db, DDoc, 0, 500).
+    couch_stats:increment_counter([dreyfus, active_searches]),
+    try
+        handle_search_req(Req, Db, DDoc, 0, 500)
+    after
+        couch_stats:decrement_counter([dreyfus, active_searches])
+    end.
 
 handle_search_req(
     #httpd{method = Method, path_parts = [_, _, _, _, IndexName]} = Req,