Re-materialize views for out of sync discussion topics

fixes ADMIN-689
relates to https://gerrit.instructure.com/#/c/138106/

Test plan
- Run and make sure it doesn't error

Change-Id: I761f125205ba09f2e96064ffe956c535b8f87fa7
Reviewed-on: https://gerrit.instructure.com/138340
Reviewed-by: Cody Cutrer <cody@instructure.com>
Reviewed-by: Steven Burnett <sburnett@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Jeremy Stanley <jeremy@instructure.com>
Tested-by: Jenkins
Product-Review: Mysti Sadler <mysti@instructure.com>

db/migrate/20180118182039_fix_discussion_topic_materialized_views.rb

@@ -0,0 +1,29 @@
+#
+# Copyright (C) 2018 - present Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the Free
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+
+class FixDiscussionTopicMaterializedViews < ActiveRecord::Migration[5.0]
+  tag :postdeploy
+
+  def up
+    DataFixup::FixDiscussionTopicMaterializedViews.send_later_if_production_enqueue_args(:run,
+      priority: Delayed::LOW_PRIORITY,
+      n_strand: 'long_datafixups')
+  end
+
+  def down
+  end
+end

lib/data_fixup/fix_discussion_topic_materialized_views.rb

@@ -0,0 +1,51 @@
+#
+# Copyright (C) 2018 - present Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the Free
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+
+module DataFixup
+  class FixDiscussionTopicMaterializedViews
+    def self.run
+      topic_ids = nil
+      Shackles.activate(:slave) do
+        result = ActiveRecord::Base.connection.execute(
+          "with entries as (
+            select count(*) as c, discussion_topic_id
+              from #{DiscussionEntry.quoted_table_name}
+             group by discussion_topic_id
+            ) , matview as (
+            select coalesce(array_length(regexp_split_to_array(entry_ids_array, E'\n'), 1) -2,0) as c
+             , discussion_topic_id
+             from #{DiscussionTopic::MaterializedView.quoted_table_name}
+            where generation_started_at < now() - interval '10 minutes'
+          )
+          select entries.discussion_topic_id as topic
+               , entries.c as ent
+               , matview.c as mat
+            from matview,entries
+           where matview.discussion_topic_id=entries.discussion_topic_id
+             and matview.c != entries.c;")
+
+         topic_ids = result.map{|d| d['topic']}
+      end
+
+      Shackles.activate(:master) do
+        DiscussionTopic.where(id: topic_ids).find_each do |dt|
+          DiscussionTopic::MaterializedView.for(dt).update_materialized_view_without_send_later
+        end
+      end
+    end
+  end
+end