Skip 3 expensive calls for jobs saving in 'waiting' status on Unified…

…Job (ansible#15174)

skip update parent logic for 'waiting' on UnifiedJob

by not looking up "status_before" from previous instance
we save 2 to 3 expensive calls (the self lookup of old state, the lookup
of parent, and the update to parent if allow_simultaneous == False or status == 'waiting')

awx/main/models/unified_jobs.py

@@ -823,7 +823,7 @@ def parent_instance_set(key, val):
                 update_fields.append(key)
 
         if parent_instance:
-            if self.status in ('pending', 'waiting', 'running'):
+            if self.status in ('pending', 'running'):
                 if parent_instance.current_job != self:
                     parent_instance_set('current_job', self)
                 # Update parent with all the 'good' states of it's child
@@ -860,7 +860,7 @@ def save(self, *args, **kwargs):
         # If this job already exists in the database, retrieve a copy of
         # the job in its prior state.
         # If update_fields are given without status, then that indicates no change
-        if self.pk and ((not update_fields) or ('status' in update_fields)):
+        if self.status != 'waiting' and self.pk and ((not update_fields) or ('status' in update_fields)):
             self_before = self.__class__.objects.get(pk=self.pk)
             if self_before.status != self.status:
                 status_before = self_before.status
@@ -902,7 +902,8 @@ def save(self, *args, **kwargs):
                 update_fields.append('elapsed')
 
         # Ensure that the job template information is current.
-        if self.unified_job_template != self._get_parent_instance():
+        # unless status is 'waiting', because this happens in large batches at end of task manager runs and is blocking
+        if self.status != 'waiting' and self.unified_job_template != self._get_parent_instance():
             self.unified_job_template = self._get_parent_instance()
             if 'unified_job_template' not in update_fields:
                 update_fields.append('unified_job_template')
@@ -915,8 +916,9 @@ def save(self, *args, **kwargs):
         # Okay; we're done. Perform the actual save.
         result = super(UnifiedJob, self).save(*args, **kwargs)
 
-        # If status changed, update the parent instance.
-        if self.status != status_before:
+        # If status changed, update the parent instance
+        # unless status is 'waiting', because this happens in large batches at end of task manager runs and is blocking
+        if self.status != status_before and self.status != 'waiting':
             # Update parent outside of the transaction for Job w/ allow_simultaneous=True
             # This dodges lock contention at the expense of the foreign key not being
             # completely correct.