Fix memory leak related to cached lookups

* It turned out that Mistral used a lot of memory because it
  used cached DB lookups for task executions (only task executions
  in a terminal state get cached) and the maximum size of the cache
  was too big, 20000 entries. One task execution in certain cases
  may take a lot of memory (e.g. several megabytes) so 20000 objects
  make memory footprint huge. Additionally, when a workflow completes
  we need to invalidate coresponding task executions in the cache.
  This didn't happen before this patch.
* This patch fixes the aforementioned issues by using partial
  invalidation of the cache and setting smaller cache size.
* Fixed "Starting workflow .." log statement to not print the entire
  structure of the workflow definition into the workflow log, only its
  name and input parameters
* Minor style fixes

Change-Id: I0ee300f631a4bdfa2f618c2a10048267f27b3345
Closes-bug: #1664864

mistral/api/controllers/v2/resources.py

@@ -354,7 +354,7 @@ class ActionExecution(resource.Resource):
     output = types.jsontype
     created_at = wtypes.text
     updated_at = wtypes.text
-    params = types.jsontype
+    params = types.jsontype  # TODO(rakhmerov): What is this??
 
     @classmethod
     def sample(cls):

mistral/engine/default_engine.py

@@ -38,7 +38,6 @@ class DefaultEngine(base.Engine):
     @profiler.trace('engine-start-workflow')
     def start_workflow(self, wf_identifier, wf_input, description='',
                        **params):
-
         with db_api.transaction():
             wf_ex = wf_handler.start_workflow(
                 wf_identifier,

mistral/engine/workflows.py

@@ -81,7 +81,11 @@ class Workflow(object):
 
         assert not self.wf_ex
 
-        wf_trace.info(self.wf_ex, "Starting workflow: %s" % self.wf_def)
+        wf_trace.info(
+            self.wf_ex,
+            "Starting workflow [name=%s, input=%s]" %
+            (self.wf_def.name, utils.cut(input_dict))
+        )
 
         # TODO(rakhmerov): This call implicitly changes input_dict! Fix it!
         # After fix we need to move validation after adding risky fields.
@@ -147,7 +151,7 @@ class Workflow(object):
         # Since some lookup utils functions may use cache for completed tasks
         # we need to clean caches to make sure that stale objects can't be
         # retrieved.
-        lookup_utils.clean_caches()
+        lookup_utils.clear_caches()
 
         wf_service.update_workflow_execution_env(self.wf_ex, env)
 
@@ -258,6 +262,11 @@ class Workflow(object):
         # only if it completed successfully or failed.
         self.wf_ex.accepted = states.is_completed(state)
 
+        if states.is_completed(state):
+            # No need to keep task executions of this workflow in the
+            # lookup cache anymore.
+            lookup_utils.invalidate_cached_task_executions(self.wf_ex.id)
+
         if recursive and self.wf_ex.task_execution_id:
             parent_task_ex = db_api.get_task_execution(
                 self.wf_ex.task_execution_id

mistral/tests/unit/base.py

@@ -248,7 +248,7 @@ class DbTestCase(BaseTest):
         action_manager.sync_db()
 
     def _clean_db(self):
-        lookup_utils.clean_caches()
+        lookup_utils.clear_caches()
 
         contexts = [
             get_context(default=False),

mistral/tests/unit/engine/test_lookup_utils.py

@@ -0,0 +1,82 @@
+# Copyright 2017 - Nokia Networks.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#        http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS,
+#    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#    See the License for the specific language governing permissions and
+#    limitations under the License.
+
+from oslo_config import cfg
+
+from mistral.db.v2 import api as db_api
+from mistral.services import workflows as wf_service
+from mistral.tests.unit.engine import base
+from mistral.workflow import lookup_utils
+from mistral.workflow import states
+
+# Use the set_default method to set value otherwise in certain test cases
+# the change in value is not permanent.
+cfg.CONF.set_default('auth_enable', False, group='pecan')
+
+
+class LookupUtilsTest(base.EngineTestCase):
+    def test_task_execution_cache_invalidation(self):
+        wf_text = """---
+        version: '2.0'
+
+        wf:
+          tasks:
+            task1:
+              action: std.noop
+              on-success: join_task
+
+            task2:
+              action: std.noop
+              on-success: join_task
+
+            join_task:
+              join: all
+              on-success: task4
+
+            task4:
+              action: std.noop
+              pause-before: true
+        """
+
+        wf_service.create_workflows(wf_text)
+
+        # Start workflow.
+        wf_ex = self.engine.start_workflow('wf', {})
+
+        self.await_workflow_paused(wf_ex.id)
+
+        with db_api.transaction():
+            # Note: We need to reread execution to access related tasks.
+            wf_ex = db_api.get_workflow_execution(wf_ex.id)
+
+            tasks = wf_ex.task_executions
+
+        self.assertEqual(4, len(tasks))
+
+        self._assert_single_item(tasks, name='task1', state=states.SUCCESS)
+        self._assert_single_item(tasks, name='task2', state=states.SUCCESS)
+        self._assert_single_item(tasks, name='join_task', state=states.SUCCESS)
+        self._assert_single_item(tasks, name='task4', state=states.IDLE)
+
+        # Expecting one cache entry because we know that 'join' operation
+        # uses cached lookups and the workflow is not finished yet.
+        self.assertEqual(1, lookup_utils.get_task_execution_cache_size())
+
+        self.engine.resume_workflow(wf_ex.id)
+
+        self.await_workflow_success(wf_ex.id)
+
+        # Expecting that the cache size is 0 because the workflow has
+        # finished and invalidated corresponding cache entry.
+        self.assertEqual(0, lookup_utils.get_task_execution_cache_size())

mistral/workflow/lookup_utils.py

@@ -35,8 +35,21 @@ import threading
 from mistral.db.v2 import api as db_api
 from mistral.workflow import states
 
-_TASK_EXECUTIONS_CACHE_LOCK = threading.RLock()
-_TASK_EXECUTIONS_CACHE = cachetools.LRUCache(maxsize=20000)
+
+def _create_lru_cache_for_workflow_execution(wf_ex_id):
+    return cachetools.LRUCache(maxsize=500)
+
+# This is a two-level caching structure.
+# First level: [<workflow execution id> -> <task execution cache>]
+# Second level (task execution cache): [<task_name> -> <task executions>]
+# The first level (by workflow execution id) allows to invalidate
+# needed cache entry when the workflow gets completed.
+_TASK_EX_CACHE = cachetools.LRUCache(
+    maxsize=100,
+    missing=_create_lru_cache_for_workflow_execution
+)
+
+_CACHE_LOCK = threading.RLock()
 
 
 def find_task_executions_by_name(wf_ex_id, task_name):
@@ -46,10 +59,8 @@ def find_task_executions_by_name(wf_ex_id, task_name):
     :param task_name: Task name.
     :return: Task executions (possibly a cached value).
     """
-    cache_key = (wf_ex_id, task_name)
-
-    with _TASK_EXECUTIONS_CACHE_LOCK:
-        t_execs = _TASK_EXECUTIONS_CACHE.get(cache_key)
+    with _CACHE_LOCK:
+        t_execs = _TASK_EX_CACHE[wf_ex_id].get(task_name)
 
     if t_execs:
         return t_execs
@@ -66,8 +77,8 @@ def find_task_executions_by_name(wf_ex_id, task_name):
     )
 
     if all_finished:
-        with _TASK_EXECUTIONS_CACHE_LOCK:
-            _TASK_EXECUTIONS_CACHE[cache_key] = t_execs
+        with _CACHE_LOCK:
+            _TASK_EX_CACHE[wf_ex_id][task_name] = t_execs
 
     return t_execs
 
@@ -108,6 +119,16 @@ def find_completed_tasks(wf_ex_id):
     return db_api.get_completed_task_executions(workflow_execution_id=wf_ex_id)
 
 
-def clean_caches():
-    with _TASK_EXECUTIONS_CACHE_LOCK:
-        _TASK_EXECUTIONS_CACHE.clear()
+def get_task_execution_cache_size():
+    return len(_TASK_EX_CACHE)
+
+
+def invalidate_cached_task_executions(wf_ex_id):
+    with _CACHE_LOCK:
+        if wf_ex_id in _TASK_EX_CACHE:
+            del _TASK_EX_CACHE[wf_ex_id]
+
+
+def clear_caches():
+    with _CACHE_LOCK:
+        _TASK_EX_CACHE.clear()