Merge "Optimize final workflow context evaluation with a batch request"

mistral/db/v2/api.py

@@ -312,6 +312,10 @@ def get_completed_task_executions(**kwargs):
     return IMPL.get_completed_task_executions(**kwargs)
 
 
+def get_completed_task_executions_as_batches(**kwargs):
+    return IMPL.get_completed_task_executions_as_batches(**kwargs)
+
+
 def get_incomplete_task_executions(**kwargs):
     return IMPL.get_incomplete_task_executions(**kwargs)
 

mistral/db/v2/sqlalchemy/api.py

@@ -876,6 +876,30 @@ def get_completed_task_executions(session=None, **kwargs):
     return query.all()
 
 
+@b.session_aware()
+def get_completed_task_executions_as_batches(session=None, **kwargs):
+    # NOTE: Using batch querying seriously allows to optimize memory
+    # consumption on operations when we need to iterate through
+    # a list of task executions and do some processing like merging
+    # their inbound contexts. If we don't use batches Mistral has to
+    # hold all the collection (that can be large) in memory.
+    # Using a generator that returns batches lets GC to collect a
+    # batch of task executions that has already been processed.
+    query = _get_completed_task_executions_query(kwargs)
+
+    # Batch size 20 may be arguable but still seems reasonable: it's big
+    # enough to keep the total number of DB hops small (say for 100 tasks
+    # we'll need only 5) and small enough not to drastically increase
+    # memory footprint if the number of tasks is big like several hundreds.
+    batch_size = 20
+    idx = 0
+
+    while idx < query.count():
+        yield query.slice(idx, idx + batch_size).all()
+
+        idx += batch_size
+
+
 def _get_incomplete_task_executions_query(kwargs):
     query = b.model_query(models.TaskExecution)
 

mistral/tests/unit/engine/test_direct_workflow.py

@@ -945,9 +945,9 @@ class DirectWorkflowEngineTest(base.EngineTestCase):
         with db_api.transaction():
             wf_ex = db_api.get_workflow_execution(wf_ex.id)
 
-            tasks = wf_ex.task_executions
+            task_execs = wf_ex.task_executions
 
-        self.assertEqual(task_cnt + 3, len(tasks))
+        self.assertEqual(task_cnt + 3, len(task_execs))
 
-        self._assert_single_item(tasks, name='task0')
-        self._assert_single_item(tasks, name='task{}'.format(task_cnt))
+        self._assert_single_item(task_execs, name='task0')
+        self._assert_single_item(task_execs, name='task{}'.format(task_cnt))

mistral/workflow/direct_workflow.py

@@ -168,11 +168,15 @@ class DirectWorkflowController(base.WorkflowController):
     def evaluate_workflow_final_context(self):
         ctx = {}
 
-        for t_ex in self._find_end_task_executions():
-            ctx = utils.merge_dicts(
-                ctx,
-                data_flow.evaluate_task_outbound_context(t_ex)
-            )
+        for batch in self._find_end_task_executions_as_batches():
+            if not batch:
+                break
+
+            for t_ex in batch:
+                ctx = utils.merge_dicts(
+                    ctx,
+                    data_flow.evaluate_task_outbound_context(t_ex)
+                )
 
         return ctx
 
@@ -208,7 +212,7 @@ class DirectWorkflowController(base.WorkflowController):
 
         return True
 
-    def _find_end_task_executions(self):
+    def _find_end_task_executions_as_batches(self):
         def is_end_task(t_ex):
             try:
                 return not self._has_outbound_tasks(t_ex)
@@ -219,13 +223,15 @@ class DirectWorkflowController(base.WorkflowController):
                 # of given task also.
                 return True
 
-        return list(
-            filter(
-                is_end_task,
-                lookup_utils.find_completed_task_executions(self.wf_ex.id)
-            )
+        batches = lookup_utils.find_completed_task_executions_as_batches(
+            self.wf_ex.id
         )
 
+        for batch in batches:
+            yield list(
+                filter(is_end_task, batch)
+            )
+
     def _has_outbound_tasks(self, task_ex):
         # In order to determine if there are outbound tasks we just need
         # to calculate next task names (based on task outbound context)

mistral/workflow/lookup_utils.py

@@ -151,6 +151,12 @@ def find_completed_task_executions(wf_ex_id):
     return db_api.get_completed_task_executions(workflow_execution_id=wf_ex_id)
 
 
+def find_completed_task_executions_as_batches(wf_ex_id):
+    return db_api.get_completed_task_executions_as_batches(
+        workflow_execution_id=wf_ex_id
+    )
+
+
 def get_task_execution_cache_size():
     return len(_TASK_EX_CACHE)