only run cursor.count when requested (#2469)

superdesk/datalayer.py

@@ -53,14 +53,16 @@ def init_elastic(self, app, raise_on_mapping_error=False):
                 finally:
                     unlock("elastic")
 
-    def find(self, resource, req, lookup, perform_count=None):
+    def find(self, resource, req, lookup, perform_count=True):
         cursor = superdesk.get_resource_service(resource).get(req=req, lookup=lookup)
-        return cursor, cursor.count()
+        if perform_count:
+            return cursor, cursor.count()
+        return cursor, None
 
     def find_all(self, resource, max_results=1000):
         req = ParsedRequest()
         req.max_results = max_results
-        cursor, count = self._backend(resource).find(resource, req, None)
+        cursor, _ = self._backend(resource).find(resource, req, None, perform_count=False)
         return cursor
 
     def find_one(self, resource, req, check_auth_value=True, force_auth_field_projection=False, **lookup):

superdesk/eve_backend.py

@@ -125,12 +125,12 @@ def get(self, endpoint_name, req, lookup, **kwargs):
         backend = self._lookup_backend(endpoint_name, fallback=True)
         is_mongo = self._backend(endpoint_name) == backend
 
-        cursor, count = backend.find(endpoint_name, req, lookup)
+        cursor, count = backend.find(endpoint_name, req, lookup, perform_count=req.if_modified_since)
 
         if req.if_modified_since and count:
             # fetch all items, not just updated
             req.if_modified_since = None
-            cursor, count = backend.find(endpoint_name, req, lookup)
+            cursor, count = backend.find(endpoint_name, req, lookup, perform_count=False)
 
         source_config = app.config["DOMAIN"][endpoint_name]
         if is_mongo and source_config.get("collation"):