sendalerts was not using the api_check (status, user_id, alert_after) index so removing it. The index was not selective enough.

hc/api/management/commands/sendalerts.py

@@ -28,7 +28,7 @@ def notify_on_thread(check_id, stdout):
 
 class Command(BaseCommand):
     help = 'Sends UP/DOWN email alerts'
-    owned = Check.objects.filter(user__isnull=False)
+    owned = Check.objects.filter(user__isnull=False).order_by("alert_after")
 
     def add_arguments(self, parser):
         parser.add_argument(

hc/api/migrations/0036_auto_20180116_2243.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.6 on 2018-01-16 22:43
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('api', '0035_auto_20171229_2008'),
+    ]
+
+    operations = [
+        migrations.AlterIndexTogether(
+            name='check',
+            index_together=set([]),
+        ),
+    ]

hc/api/models.py

@@ -57,11 +57,6 @@ def isostring(dt):
 
 
 class Check(models.Model):
-
-    class Meta:
-        # sendalerts command will query using these
-        index_together = ["status", "user", "alert_after"]
-
     name = models.CharField(max_length=100, blank=True)
     tags = models.CharField(max_length=500, blank=True)
     code = models.UUIDField(default=uuid.uuid4, editable=False, db_index=True)