Fix workflow execution cascade delete error

If the cascade deletion error is identified, then resort to
recursively deleting the subworkflows before deleting the
given execution.

Closes-Bug: https://bugs.launchpad.net/mistral/+bug/1832300
Change-Id: I6e0d9db93e103eaf3a329dfa1b4153975c135008

mistral/db/v2/sqlalchemy/api.py

@@ -16,6 +16,7 @@
 
 import contextlib
 import datetime
+import re
 import sys
 import threading
 
@@ -889,13 +890,59 @@ def delete_workflow_execution(id, session=None):
     insecure = context.ctx().is_admin
     query = b.model_query(model) if insecure else _secure_query(model)
 
-    count = query.filter(
-        models.WorkflowExecution.id == id).delete()
+    try:
+        count = query.filter(
+            models.WorkflowExecution.id == id
+        ).delete()
 
-    if count == 0:
-        raise exc.DBEntityNotFoundError(
-            "WorkflowExecution not found [id=%s]" % id
-        )
+        if count == 0:
+            raise exc.DBEntityNotFoundError(
+                "WorkflowExecution not found [id=%s]" % id
+            )
+    except db_exc.DBError as e:
+        if is_mysql_max_depth_error(e) or is_mariadb_max_depth_error(e):
+            # https://bugs.launchpad.net/mistral/+bug/1832300
+            # mysql cascade delete error
+            delete_workflow_execution_recurse(id)
+        else:
+            raise
+
+
+def is_mysql_max_depth_error(e):
+    pattern = ".*3008.*Foreign key cascade delete" \
+              "/update exceeds max depth of 15.*"
+    return re.match(pattern, str(e))
+
+
+def is_mariadb_max_depth_error(e):
+    pattern = ".*Got error 193.*ON DELETE CASCADE.*"
+    return re.match(pattern, str(e))
+
+
+def delete_workflow_execution_recurse(wf_ex_id):
+    sub_wf_ex_ids = _get_all_direct_subworkflows(wf_ex_id)
+
+    for sub_wf_ex_id in sub_wf_ex_ids:
+        delete_workflow_execution(sub_wf_ex_id)
+
+    delete_workflow_execution(wf_ex_id)
+
+
+def _get_all_direct_subworkflows(wf_ex_id):
+    model = models.WorkflowExecution
+    insecure = context.ctx().is_admin
+    if insecure:
+        query = b.model_query(model, columns=['id'])
+    else:
+        query = _secure_query(model, model.id)
+    query = query.join(
+        models.TaskExecution,
+        models.WorkflowExecution.task_execution_id == models.TaskExecution.id
+    ).filter(
+        models.TaskExecution.workflow_execution_id == wf_ex_id
+    )
+
+    return [i[0] for i in query.all()]
 
 
 @b.session_aware()

mistral/tests/unit/db/v2/test_sqlalchemy_db_api.py

@@ -3376,3 +3376,35 @@ class LockTest(SQLAlchemyTest):
 
         # Make sure that outside 'with' section the lock record does not exist.
         self.assertEqual(0, len(db_api.get_named_locks()))
+
+    def test_internal_get_direct_subworkflows(self):
+        def wex(wex_id, tex_id=None):
+            db_api.create_workflow_execution(
+                {'id': wex_id, 'name': wex_id, 'task_execution_id': tex_id}
+            )
+
+        def tex(tex_id, wex_id):
+            db_api.create_task_execution(
+                {'id': tex_id, 'name': tex_id, 'workflow_execution_id': wex_id}
+            )
+
+        def assert_subworkflows(expected):
+            self.assertEqual(
+                set(expected), set(db_api._get_all_direct_subworkflows('root'))
+            )
+
+        wex('root')
+        tex('t1', 'root')
+        wex('sub1', 't1')
+
+        assert_subworkflows(['sub1'])
+
+        tex('t2', 'root')
+        wex('sub2', 't1')
+
+        assert_subworkflows(['sub1', 'sub2'])
+
+        tex('sub1t1', 'sub1')
+        wex('sub1sub1', 'sub1t1')
+
+        assert_subworkflows(['sub1', 'sub2'])

mistral/tests/unit/engine/test_subworkflows.py

@@ -501,3 +501,38 @@ class SubworkflowsTest(base.EngineTestCase):
         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()))
+
+    def test_cascade_delete_deep(self):
+        wf_text = """
+        version: 2.0
+
+        wf:
+          input:
+            - level
+          tasks:
+            initial:
+              action: std.noop
+              on-success:
+                - recurse: <% $.level > 0 %>
+
+            recurse:
+              workflow: wf
+              input:
+                level: <% $.level - 1 %>
+        """
+
+        wf_service.create_workflows(wf_text)
+
+        wf_ex = self.engine.start_workflow('wf', wf_input={"level": 7})
+
+        self.await_workflow_success(wf_ex.id)
+
+        self.assertEqual(8, len(db_api.get_workflow_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()))