Add user index to comment_bank_items

refs EVAL-1677
flag=assignment_comment_library

test-plan:
- run migrations and assert a new user index was added
to the comment_bank_items table and the course, user index
was removed
- revert the migration and assert the course, user index was
added and the user index was removed

Change-Id: Ib7a2619718477a0c06d2db0dce09f2a5f3d81da8
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/264857
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>

db/migrate/20210510184336_add_user_index_comment_bank_items.rb

@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+#
+# Copyright (C) 2021 - 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 AddUserIndexCommentBankItems < ActiveRecord::Migration[6.0]
+  disable_ddl_transaction!
+  tag :predeploy
+
+  def change
+    remove_index :comment_bank_items,
+                 algorithm: :concurrently,
+                 column: [:course_id, :user_id],
+                 where: "workflow_state <> 'deleted'",
+                 name: :index_comment_bank_items_on_course_and_user,
+                 if_exists: true
+
+    add_index :comment_bank_items,
+              :user_id,
+              algorithm: :concurrently,
+              name: 'index_active_comment_bank_items_on_user',
+              where: "workflow_state <> 'deleted'",
+              if_not_exists: true
+
+    add_index :comment_bank_items,
+              :course_id,
+              algorithm: :concurrently,
+              if_not_exists: true
+
+    add_index :comment_bank_items,
+              :user_id,
+              algorithm: :concurrently,
+              if_not_exists: true
+  end
+end