PERF: much faster Badge.ensure_consistency

app/models/badge.rb

@@ -137,7 +137,19 @@ class Badge < ActiveRecord::Base
               AND user_badges.id = ub.id
     SQL
 
-    Badge.find_each(&:reset_grant_count!)
+    exec_sql <<-SQL.squish
+      WITH X AS (
+          SELECT badge_id
+               , COUNT(user_id) users
+            FROM user_badges
+        GROUP BY badge_id
+      )
+      UPDATE badges
+         SET grant_count = X.users
+        FROM X
+       WHERE id = X.badge_id
+         AND grant_count <> X.users
+    SQL
   end
 
   def awarded_for_trust_level?