remove intermediary _is_clone_of entries when cloning

Improvements in memory usage by the ORM, removing a significant set of
intermediary expression objects that are typically stored when a copy of an
expression object is created. These clones have been greatly reduced,
reducing the number of total expression objects stored in memory by
ORM mappings by about 30%.

note this change causes the tests to have a bit of a harder time with
GC, which we would assume is because mappings now have a lot more
garbage to clean up after mappers are configured.   it remains
to be seen what the long term effects of this are.

Fixes: #7823
Change-Id: If8729747ffb9bf27e8974f069a994b5a823ee095

1 files changed, 13 insertions, 0 deletions

diff --git a/test/aaa_profiling/test_memusage.py b/test/aaa_profiling/test_memusage.py
index cf89dd6e2..f084eac2c 100644
--- a/test/aaa_profiling/test_memusage.py
+++ b/test/aaa_profiling/test_memusage.py
@@ -346,6 +346,19 @@ class MemUsageTest(EnsureZeroed):
 
         go()
 
+    def test_clone_expression(self):
+
+        root_expr = column("x", Integer) == 12
+        expr = root_expr
+
+        @profile_memory()
+        def go():
+            nonlocal expr
+
+            expr = cloned_traverse(expr, {}, {})
+
+        go()
+
 
 @testing.add_to_marker.memory_intensive
 class MemUsageWBackendTest(fixtures.MappedTest, EnsureZeroed):