Add the `pruneflips` management command.

CHANGELOG.md

@@ -6,6 +6,7 @@ All notable changes to this project will be documented in this file.
 ### Improvements
 - Show the number of downtimes and total downtime minutes in monthly reports (#104)
 - Show the number of downtimes and total downtime minutes in "Check Details" page
+- Add the `pruneflips` management command
 
 
 ## 1.8.0 - 2019-07-08

README.md

@@ -269,7 +269,7 @@ There are separate Django management commands for each task:
     $ ./manage.py pruneusers
     ```
 
-* Remove old records fromt he `api_tokenbucket` table. The TokenBucket
+* Remove old records from the `api_tokenbucket` table. The TokenBucket
   model is used for rate-limiting login attempts and similar operations.
   Any records older than one day can be safely removed.
 
@@ -277,6 +277,15 @@ There are separate Django management commands for each task:
     $ ./manage.py prunetokenbucket
     ```
 
+* Remove old records from the `api_flip` table. The Flip
+  objects are used to track status changes of checks, and to calculate
+  downtime statistics month by month. Flip objects from more than 3 months
+  ago are not used and can be safely removed.
+
+    ```
+    $ ./manage.py pruneflips
+    ```
+
 When you first try these commands on your data, it is a good idea to
 test them on a copy of your database, not on the live database right away.
 In a production setup, you should also have regular, automated database

hc/api/management/commands/pruneflips.py

@@ -0,0 +1,16 @@
+from django.core.management.base import BaseCommand
+
+from hc.api.models import Flip
+from hc.lib.date import month_boundaries
+
+
+class Command(BaseCommand):
+    help = "Prune old Flip objects."
+
+    def handle(self, *args, **options):
+        threshold = min(month_boundaries(months=3))
+
+        q = Flip.objects.filter(created__lt=threshold)
+        n_pruned, _ = q.delete()
+
+        return "Done! Pruned %d flips." % n_pruned