Revert "Skip incompatible migration entirely"

This reverts commit 545eb6385d73efb004dd73535adc5279cd7b7a92.

db/migrate/20180812173710_copy_status_stats.rb

@@ -2,19 +2,18 @@ class CopyStatusStats < ActiveRecord::Migration[5.2]
   disable_ddl_transaction!
 
   def up
-    # FIXME upserts don't work in PostgreSQL 9.4, so we're skipping this for now.
+    safety_assured do
-    # safety_assured do
+      Status.unscoped.select('id').find_in_batches(batch_size: 5_000) do |statuses|
-    #   Status.unscoped.select('id').find_in_batches(batch_size: 5_000) do |statuses|
+        execute <<-SQL.squish
-    #     execute <<-SQL.squish
+          INSERT INTO status_stats (status_id, reblogs_count, favourites_count, created_at, updated_at)
-    #       INSERT INTO status_stats (status_id, reblogs_count, favourites_count, created_at, updated_at)
+          SELECT id, reblogs_count, favourites_count, created_at, updated_at
-    #       SELECT id, reblogs_count, favourites_count, created_at, updated_at
+          FROM statuses
-    #       FROM statuses
+          WHERE id IN (#{statuses.map(&:id).join(', ')})
-    #       WHERE id IN (#{statuses.map(&:id).join(', ')})
+          ON CONFLICT (status_id) DO UPDATE
-    #       ON CONFLICT (status_id) DO UPDATE
+          SET reblogs_count = EXCLUDED.reblogs_count, favourites_count = EXCLUDED.favourites_count
-    #       SET reblogs_count = EXCLUDED.reblogs_count, favourites_count = EXCLUDED.favourites_count
+        SQL
-    #     SQL
+      end
-    #   end
+    end
-    # end
   end
 
   def down