adjustments for unreliable gc

sporadic (and at the moment persistent) test failures
related to aiosqlite seem to have in common that Python
gc stops working fully when we run a lot of tests with
aiosqlite.  The failures are not limited to aiosqlite
as they are more involving places where we assume or
expect gc.collect() to get rid of things, and it doesn't.

Identify (based on reproducible case on the d3 CI runner)
the spots where this happens and add fixes.

test/orm/test_transaction.py test_gced_delete_on_rollback
has always been a very sensitive test with a lot of issues,
so here we move it to the test_memusage suite and limit
it only to when the memusage suite is running.

Change-Id: I683412d0effe8732c45980b40722e5bb63431177

5 files changed, 60 insertions, 39 deletions

diff --git a/doc/build/orm/queryguide/_deferred_setup.rst b/doc/build/orm/queryguide/_deferred_setup.rst
index e75630c46..2675c9341 100644
--- a/doc/build/orm/queryguide/_deferred_setup.rst
+++ b/doc/build/orm/queryguide/_deferred_setup.rst
@@ -100,5 +100,6 @@ This page illustrates the mappings and fixture data used by the
     ... )
     >>> session.commit()
     BEGIN ... COMMIT
+    >>> session.close()
     >>> conn.begin()
     BEGIN ...
diff --git a/doc/build/orm/queryguide/select.rst b/doc/build/orm/queryguide/select.rst
index 7967bb4d5..55c3ae94e 100644
--- a/doc/build/orm/queryguide/select.rst
+++ b/doc/build/orm/queryguide/select.rst
@@ -1001,6 +1001,10 @@ which belonged to "sandy":
 Relationship Instance Comparison Operators
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+.. comment
+
+    >>> session.expunge_all()
+
 The :func:`_orm.relationship`-bound attribute also offers a few SQL construction
 implementations that are geared towards filtering a :func:`_orm.relationship`-bound
 attribute in terms of a specific instance of a related object, which can unpack
diff --git a/test/aaa_profiling/test_memusage.py b/test/aaa_profiling/test_memusage.py
index 1162a54af..4756a3fd5 100644
--- a/test/aaa_profiling/test_memusage.py
+++ b/test/aaa_profiling/test_memusage.py
@@ -18,6 +18,7 @@ from sqlalchemy import util
 from sqlalchemy.engine import result
 from sqlalchemy.engine.processors import to_decimal_processor_factory
 from sqlalchemy.orm import aliased
+from sqlalchemy.orm import attributes
 from sqlalchemy.orm import clear_mappers
 from sqlalchemy.orm import configure_mappers
 from sqlalchemy.orm import declarative_base
@@ -1724,3 +1725,56 @@ class CycleTest(_fixtures.FixtureTest):
             s.close()
 
         go()
+
+
+@testing.add_to_marker.memory_intensive
+class MiscMemoryIntensiveTests(fixtures.TestBase):
+    @testing.fixture
+    def user_fixture(self, decl_base):
+        class User(decl_base):
+            __tablename__ = "user"
+
+            id = Column(Integer, primary_key=True)
+            name = Column(String(50))
+
+        decl_base.metadata.create_all(testing.db)
+        yield User
+
+    @testing.requires.predictable_gc
+    def test_gced_delete_on_rollback(self, user_fixture):
+        User = user_fixture
+
+        s = fixture_session()
+        u1 = User(name="ed")
+        s.add(u1)
+        s.commit()
+
+        s.delete(u1)
+        u1_state = attributes.instance_state(u1)
+        assert u1_state in s.identity_map.all_states()
+        assert u1_state in s._deleted
+        s.flush()
+        assert u1_state not in s.identity_map.all_states()
+        assert u1_state not in s._deleted
+        del u1
+        gc_collect()
+        gc_collect()
+        gc_collect()
+        assert u1_state.obj() is None
+
+        s.rollback()
+        # new in 1.1, not in identity map if the object was
+        # gc'ed and we restore snapshot; we've changed update_impl
+        # to just skip this object
+        assert u1_state not in s.identity_map.all_states()
+
+        # in any version, the state is replaced by the query
+        # because the identity map would switch it
+        u1 = s.query(User).filter_by(name="ed").one()
+        assert u1_state not in s.identity_map.all_states()
+
+        eq_(s.scalar(select(func.count("*")).select_from(User.__table__)), 1)
+        s.delete(u1)
+        s.flush()
+        eq_(s.scalar(select(func.count("*")).select_from(User.__table__)), 0)
+        s.commit()
diff --git a/test/orm/test_transaction.py b/test/orm/test_transaction.py
index 2f08080ad..f66908fc9 100644
--- a/test/orm/test_transaction.py
+++ b/test/orm/test_transaction.py
@@ -1249,45 +1249,6 @@ class AutoExpireTest(_LocalFixture):
         assert u1 in s
         assert u1 not in s.deleted
 
-    @testing.requires.predictable_gc
-    def test_gced_delete_on_rollback(self):
-        User, users = self.classes.User, self.tables.users
-
-        s = fixture_session()
-        u1 = User(name="ed")
-        s.add(u1)
-        s.commit()
-
-        s.delete(u1)
-        u1_state = attributes.instance_state(u1)
-        assert u1_state in s.identity_map.all_states()
-        assert u1_state in s._deleted
-        s.flush()
-        assert u1_state not in s.identity_map.all_states()
-        assert u1_state not in s._deleted
-        del u1
-        gc_collect()
-        gc_collect()
-        gc_collect()
-        assert u1_state.obj() is None
-
-        s.rollback()
-        # new in 1.1, not in identity map if the object was
-        # gc'ed and we restore snapshot; we've changed update_impl
-        # to just skip this object
-        assert u1_state not in s.identity_map.all_states()
-
-        # in any version, the state is replaced by the query
-        # because the identity map would switch it
-        u1 = s.query(User).filter_by(name="ed").one()
-        assert u1_state not in s.identity_map.all_states()
-
-        eq_(s.scalar(select(func.count("*")).select_from(users)), 1)
-        s.delete(u1)
-        s.flush()
-        eq_(s.scalar(select(func.count("*")).select_from(users)), 0)
-        s.commit()
-
     def test_trans_deleted_cleared_on_rollback(self):
         User = self.classes.User
         s = fixture_session()
diff --git a/test/requirements.py b/test/requirements.py
index e56c944ff..5276593c9 100644
--- a/test/requirements.py
+++ b/test/requirements.py
@@ -397,6 +397,7 @@ class DefaultRequirements(SuiteRequirements):
             [
                 no_support("oracle", "Oracle XE usually can't handle these"),
                 no_support("mssql+pyodbc", "MS ODBC drivers struggle"),
+                no_support("+aiosqlite", "very unreliable driver"),
                 self._running_on_windows(),
             ]
         )