Don't include StdDev on sqlite3 mirror status query

Because this function isn't shipped by default, it makes more sense to
just omit it completely from the query we do to build the tables on this
page when in development. Substitute 0.0 for the value so the rest of
the calculations and display work as expected.

Signed-off-by: Dan McGee <dan@archlinux.org>

mirrors/utils.py

@@ -3,7 +3,7 @@
 from django.db.models import Avg, Count, Max, Min, StdDev
 from django_countries.fields import Country
 
-from main.utils import cache_function, utc_now
+from main.utils import cache_function, utc_now, database_vendor
 from .models import MirrorLog, MirrorProtocol, MirrorUrl
 
 
@@ -40,8 +40,11 @@ def get_mirror_statuses(cutoff=default_cutoff):
             success_count=Count('logs__duration'),
             last_sync=Max('logs__last_sync'),
             last_check=Max('logs__check_time'),
-            duration_avg=Avg('logs__duration'),
-            duration_stddev=StdDev('logs__duration'))
+            duration_avg=Avg('logs__duration'))
+
+    vendor = database_vendor(MirrorUrl)
+    if vendor != 'sqlite':
+        urls.annotate(duration_stddev=StdDev('logs__duration'))
 
     # The Django ORM makes it really hard to get actual average delay in the
     # above query, so run a seperate query for it and we will process the
@@ -70,6 +73,9 @@ def get_mirror_statuses(cutoff=default_cutoff):
         check_frequency = None
 
     for url in urls:
+        # fake the standard deviation for local testing setups
+        if vendor == 'sqlite':
+            setattr(url, 'duration_stddev', 0.0)
         annotate_url(url, delays)
 
     return {