Group Triples with same subject to improve performance. Sort reverse …

…order to put pattern matches with more variables last.

prez/services/query_generation/umbrella.py

@@ -97,6 +97,7 @@ def __init__(
         # for listing queries only, add an inner select to the where clause
         ss_gpotb = []
         if inner_select_tssp_list:
+            inner_select_tssp_list = sorted(inner_select_tssp_list, key=lambda x: str(x), reverse=True)  # grouping for performance
             ss_gpotb.append(TriplesBlock.from_tssp_list(inner_select_tssp_list))
         if inner_select_gpnt:
             ss_gpotb.extend(inner_select_gpnt)