Stop creating stoppage alerts once a group has reached a certain size.

dashboard/dashboard/models/stoppage_alert.py

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """The datastore model for alerts when data is no longer received for a test."""
 
 import logging
 
 from google.appengine.ext import ndb
 
 from dashboard import utils
 from dashboard.models import alert
 from dashboard.models import alert_group
 
+_MAX_GROUP_SIZE = 20
+
 
 class StoppageAlert(alert.Alert):
   """A stoppage alert is an alert for a Test no longer receiving new points.
 
   Each StoppageAlert is associated with one Test, so if a test suite gets
   deprecated or renamed, there may be a set of related StoppageAlerts created.
 
   The key for a StoppageAlert is of the form:
     [("StoppageAlertParent", <test_path>), ("StoppageAlert", <revision>)].
 
@@ skipping 58 matching lines @@
     row: A Row entity; the last Row that was put before the stoppage.
 
   Returns:
     A new StoppageAlert entity (although this entity has not yet been put.
   """
   new_alert = StoppageAlert(
       parent=ndb.Key('StoppageAlertParent', test.test_path),
       id=row.revision,
       internal_only=test.internal_only,
       sheriff=test.sheriff)
+  alert_group.GroupAlerts([new_alert], test.suite_name, 'StoppageAlert')
+  grouped_alert_keys = StoppageAlert.query(
+      StoppageAlert.group == new_alert.group).fetch(keys_only=True)
+  if len(grouped_alert_keys) >= _MAX_GROUP_SIZE:
+    # Too many stoppage alerts in this group; we don't want to put any more.
+    return None

[chrisphan, 2015/11/06 18:06:42]

Does this need to always return an entity?

[qyearsley, 2015/11/06 18:11:08]

Nope, as is in this CL, CreateStoppageAlert decides whether or not an alert
should be created and returns None if there should be none created, and the
caller is then responsible for checking if it's None. (Docstring updated.) Does
this seem OK? 

   test.stoppage_alert = new_alert.key
   test.put()
-  alert_group.GroupAlerts([new_alert], test.suite_name, 'StoppageAlert')
   return new_alert