From afb0f584c5f1218ec73b2b6ecd9d7509c1df4594 Mon Sep 17 00:00:00 2001
From: Renat Akhmerov <renat.akhmerov@gmail.com>
Date: Mon, 14 May 2018 17:09:29 +0700
Subject: [PATCH] Use "passive_deletes=True" in ORM relationships

* Using "passive_deletes=True" when configuring relationships
  with SQLAlchemy significantly reduces memory footprint when
  deleting a graph of objects (e.g. root workflow execution
  with all dependent tasks, actions and sub workflows) from DB.
  This happens because in this case SQLAlchemy doesn't load
  those dependent objects that are not yet in the session and
  rather relies on cascading mechanisms of databases which are
  activated by the proper configuration of foreign key columns.
  For example, "ON DELETE CASCADE" clause in the foreign key
  definition in case of for MySQL.
  Particularly, this change reduces memory footprint of API
  processes when deleting large graphs of executions and
  execution expiration policy mechanism where the same happens
  but on the engine side.
* Added a test to make sure that cascaded deletion works well
  with this new property.

Related-Bug: #1757966
Change-Id: I36988817fb8e7695094ef98958b8aa151208fadb
---
 mistral/cmd/launch.py                         |  1 +
 mistral/db/v2/sqlalchemy/models.py            |  9 ++--
 .../tests/unit/engine/test_subworkflows.py    | 42 +++++++++++++++++++
 3 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/mistral/cmd/launch.py b/mistral/cmd/launch.py
index e519a0903..54eb74c3f 100644
--- a/mistral/cmd/launch.py
+++ b/mistral/cmd/launch.py
@@ -101,6 +101,7 @@ def launch_notifier():
 
 def launch_api():
     server = api_service.WSGIService('mistral_api')
+
     launch_process(server, workers=server.workers)
 
 
diff --git a/mistral/db/v2/sqlalchemy/models.py b/mistral/db/v2/sqlalchemy/models.py
index 1329b81a7..b83f554ce 100644
--- a/mistral/db/v2/sqlalchemy/models.py
+++ b/mistral/db/v2/sqlalchemy/models.py
@@ -290,7 +290,8 @@ TaskExecution.action_executions = relationship(
     backref=backref('task_execution', remote_side=[TaskExecution.id]),
     cascade='all, delete-orphan',
     foreign_keys=ActionExecution.task_execution_id,
-    lazy='select'
+    lazy='select',
+    passive_deletes=True
 )
 
 sa.Index(
@@ -311,7 +312,8 @@ TaskExecution.workflow_executions = relationship(
     backref=backref('task_execution', remote_side=[TaskExecution.id]),
     cascade='all, delete-orphan',
     foreign_keys=WorkflowExecution.task_execution_id,
-    lazy='select'
+    lazy='select',
+    passive_deletes=True
 )
 
 sa.Index(
@@ -339,7 +341,8 @@ WorkflowExecution.task_executions = relationship(
     backref=backref('workflow_execution', remote_side=[WorkflowExecution.id]),
     cascade='all, delete-orphan',
     foreign_keys=TaskExecution.workflow_execution_id,
-    lazy='select'
+    lazy='select',
+    passive_deletes=True
 )
 
 sa.Index(
diff --git a/mistral/tests/unit/engine/test_subworkflows.py b/mistral/tests/unit/engine/test_subworkflows.py
index 635e70b38..7454d578f 100644
--- a/mistral/tests/unit/engine/test_subworkflows.py
+++ b/mistral/tests/unit/engine/test_subworkflows.py
@@ -21,6 +21,7 @@ from mistral import context as auth_context
 from mistral.db.v2 import api as db_api
 from mistral import exceptions as exc
 from mistral.services import workbooks as wb_service
+from mistral.services import workflows as wf_service
 from mistral.tests.unit.engine import base
 from mistral.workflow import states
 
@@ -455,3 +456,44 @@ class SubworkflowsTest(base.EngineTestCase):
         self.assertIsNone(wf1_ex.root_execution_id, None)
         self.assertEqual(wf2_ex.root_execution_id, wf1_ex.id)
         self.assertEqual(wf3_ex.root_execution_id, wf1_ex.id)
+
+    def test_cascade_delete(self):
+        wf_text = """
+        version: 2.0
+
+        wf:
+          tasks:
+            task1:
+              workflow: sub_wf1
+
+            task2:
+              workflow: sub_wf2
+
+        sub_wf1:
+          tasks:
+            task1:
+              action: std.noop
+
+        sub_wf2:
+          tasks:
+            task1:
+              action: std.noop
+        """
+
+        wf_service.create_workflows(wf_text)
+
+        wf_ex = self.engine.start_workflow('wf')
+
+        self.await_workflow_success(wf_ex.id)
+
+        self.assertEqual(3, len(db_api.get_workflow_executions()))
+        self.assertEqual(4, len(db_api.get_task_executions()))
+        self.assertEqual(2, len(db_api.get_action_executions()))
+
+        # Now delete the root workflow execution and make sure that
+        # all dependent objects are deleted as well.
+        db_api.delete_workflow_execution(wf_ex.id)
+
+        self.assertEqual(0, len(db_api.get_workflow_executions()))
+        self.assertEqual(0, len(db_api.get_task_executions()))
+        self.assertEqual(0, len(db_api.get_action_executions()))