Remove Datadog instrumentation around model saves

We added this a long time ago as part of the shift to opaque-keys, but
left it on because it's occasionally useful for spotting unusual levels
of activity for certain models. That being said, because we have so
many models now, we're generating too many differently named metrics,
which might get expensive.

This is doing the simplest thing and just removing datadog reporting
of model updates altogether.

openedx/core/djangoapps/monitoring/signals.py

-"""
-Add receivers for django signals, and feed data into the monitoring system.
-
-If a model has a class attribute 'METRIC_TAGS' that is a list of strings,
-those fields will be retrieved from the model instance, and added as tags to
-the recorded metrics.
-"""
-
-
-from django.db.models.signals import post_save, post_delete, m2m_changed, post_init
-from django.dispatch import receiver
-
-import dogstats_wrapper as dog_stats_api
-
-
-def _database_tags(action, sender, kwargs):  # pylint: disable=unused-argument
-    """
-    Return a tags for the sender and database used in django.db.models signals.
-
-    Arguments:
-        action (str): What action is being performed on the db model.
-        sender (Model): What model class is the action being performed on.
-        kwargs (dict): The kwargs passed by the model signal.
-    """
-    tags = _model_tags(kwargs, 'instance')
-    tags.append(u'action:{}'.format(action))
-
-    if 'using' in kwargs:
-        tags.append(u'database:{}'.format(kwargs['using']))
-
-    return tags
-
-
-def _model_tags(kwargs, key):
-    """
-    Return a list of all tags for all attributes in kwargs[key].MODEL_TAGS,
-    plus a tag for the model class.
-    """
-    if key not in kwargs:
-        return []
-
-    instance = kwargs[key]
-    tags = [
-        u'{}.{}:{}'.format(key, attr, getattr(instance, attr))
-        for attr in getattr(instance, 'MODEL_TAGS', [])
-    ]
-    tags.append(u'model_class:{}'.format(instance.__class__.__name__))
-    return tags
-
-
-@receiver(post_init, dispatch_uid='edxapp.monitoring.post_init_metrics')
-def post_init_metrics(sender, **kwargs):
-    """
-    Record the number of times that django models are instantiated.
-
-    Args:
-        sender (Model): The model class sending the signals.
-        using (str): The name of the database being used for this initialization (optional).
-        instance (Model instance): The instance being initialized (optional).
-    """
-    tags = _database_tags('initialized', sender, kwargs)
-
-    dog_stats_api.increment('edxapp.db.model', tags=tags)
-
-
-@receiver(post_save, dispatch_uid='edxapp.monitoring.post_save_metrics')
-def post_save_metrics(sender, **kwargs):
-    """
-    Record the number of times that django models are saved (created or updated).
-
-    Args:
-        sender (Model): The model class sending the signals.
-        using (str): The name of the database being used for this update (optional).
-        instance (Model instance): The instance being updated (optional).
-    """
-    action = 'created' if kwargs.pop('created', False) else 'updated'
-
-    tags = _database_tags(action, sender, kwargs)
-    dog_stats_api.increment('edxapp.db.model', tags=tags)
-
-
-@receiver(post_delete, dispatch_uid='edxapp.monitoring.post_delete_metrics')
-def post_delete_metrics(sender, **kwargs):
-    """
-    Record the number of times that django models are deleted.
-
-    Args:
-        sender (Model): The model class sending the signals.
-        using (str): The name of the database being used for this deletion (optional).
-        instance (Model instance): The instance being deleted (optional).
-    """
-    tags = _database_tags('deleted', sender, kwargs)
-
-    dog_stats_api.increment('edxapp.db.model', tags=tags)
-
-
-@receiver(m2m_changed, dispatch_uid='edxapp.monitoring.m2m_changed_metrics')
-def m2m_changed_metrics(sender, **kwargs):
-    """
-    Record the number of times that Many2Many fields are updated. This is separated
-    from post_save and post_delete, because it's signaled by the database model in
-    the middle of the Many2Many relationship, rather than either of the models
-    that are the relationship participants.
-
-    Args:
-        sender (Model): The model class in the middle of the Many2Many relationship.
-        action (str): The action being taken on this Many2Many relationship.
-        using (str): The name of the database being used for this deletion (optional).
-        instance (Model instance): The instance whose many-to-many relation is being modified.
-        model (Model class): The model of the class being added/removed/cleared from the relation.
-    """
-    if 'action' not in kwargs:
-        return
-
-    action = {
-        'post_add': 'm2m.added',
-        'post_remove': 'm2m.removed',
-        'post_clear': 'm2m.cleared',
-    }.get(kwargs['action'])
-
-    if not action:
-        return
-
-    tags = _database_tags(action, sender, kwargs)
-
-    if 'model' in kwargs:
-        tags.append('target_class:{}'.format(kwargs['model'].__name__))
-
-    pk_set = kwargs.get('pk_set', []) or []
-
-    dog_stats_api.increment(
-        'edxapp.db.model',
-        value=len(pk_set),
-        tags=tags
-    )

openedx/core/djangoapps/monitoring/startup.py

@@ -2,5 +2,4 @@
 Registers signal handlers at startup.
 """
 # pylint: disable=unused-import
-import openedx.core.djangoapps.monitoring.signals
 import openedx.core.djangoapps.monitoring.exceptions