Set up replica identity index for AccessToken

refs FOO-1171
flag=none

also don't backfill nulls if the column is already non-nullable

test plan:
 - migration works up and down
 - tests pass

Change-Id: I5009a2f31249643738f69a6b0d765daf89276165
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/260519
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
QA-Review: Simon Williams <simon@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>

config/initializers/active_record.rb

@@ -1511,9 +1511,16 @@ ActiveRecord::ConnectionAdapters::SchemaStatements.class_eval do
     execute schema_creation.accept(at)
   end
 
-  def add_replica_identity(table_string, column_name, default_value)
-    klass = table_string.constantize
-    DataFixup::BackfillNulls.run(klass, column_name, default_value: default_value)
+  def add_replica_identity(model_name, column_name, default_value)
+    klass = model_name.constantize
+    # when a batch of migrations includes both adding the `column_name` and
+    # calling this method (e.g. when migrating a newly created db), the cached
+    # column information can be stale, so we have to explicitly reset it here
+    # to avoid a NoMethodError
+    klass.reset_column_information
+    if klass.columns_hash[column_name.to_s].null
+      DataFixup::BackfillNulls.run(klass, column_name, default_value: default_value)
+    end
     change_column_null klass.table_name, column_name, false
     primary_column = klass.primary_key
     index_name = "index_#{klass.table_name}_replica_identity"
@@ -1521,8 +1528,8 @@ ActiveRecord::ConnectionAdapters::SchemaStatements.class_eval do
     execute(%[ALTER TABLE #{klass.quoted_table_name} REPLICA IDENTITY USING INDEX #{index_name}])
   end
 
-  def remove_replica_identity(table_string)
-    klass = table_string.constantize
+  def remove_replica_identity(model_name)
+    klass = model_name.constantize
     execute(%[ALTER TABLE #{klass.quoted_table_name} REPLICA IDENTITY DEFAULT])
     remove_index klass.table_name, name: "index_#{klass.table_name}_replica_identity", if_exists: true
   end
@@ -1814,4 +1821,4 @@ module MaxRuntimeConnectionPool
     old_connections.each(&:disconnect!)
   end
 end
-ActiveRecord::ConnectionAdapters::ConnectionPool.prepend(MaxRuntimeConnectionPool)
+ActiveRecord::ConnectionAdapters::ConnectionPool.prepend(MaxRuntimeConnectionPool)

db/migrate/20210312061714_add_replica_identity_for_access_tokens.rb

@@ -0,0 +1,33 @@
+# 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 AddReplicaIdentityForAccessTokens < ActiveRecord::Migration[6.0]
+  tag :postdeploy
+  disable_ddl_transaction!
+
+  def up
+    add_replica_identity 'AccessToken', :root_account_id, 0
+    remove_index :access_tokens, column: :root_account_id, if_exists: true
+  end
+
+  def down
+    add_index :access_tokens, :root_account_id, algorithm: :concurrently, if_not_exists: true
+    remove_replica_identity 'AccessToken'
+    change_column_null :access_tokens, :root_account_id, true
+  end
+end

spec/lib/data_fixup/populate_root_account_id_on_models_spec.rb

@@ -80,31 +80,6 @@ describe DataFixup::PopulateRootAccountIdOnModels do
       end
     end
 
-    context 'with AccessToken' do
-      it_behaves_like 'a datafixup that populates root_account_id' do
-        let(:record) do
-          dk = DeveloperKey.create!(account: @course.account)
-          at = dk.access_tokens.create!(user: user_model)
-        end
-        let(:reference_record) { @course }
-      end
-
-      context 'with_sharding' do
-        specs_require_sharding
-
-        context 'with DeveloperKey with root_account_id' do
-          it_behaves_like 'a datafixup that populates root_account_id' do
-            let(:account) { @shard1.activate { account_model } }
-            let(:record) do
-              dk = DeveloperKey.create!(account: account)
-              at = dk.access_tokens.create!(user: user_model)
-            end
-            let(:reference_record) { account }
-          end
-        end
-      end
-    end
-
     it 'should populate root_account_id on AssessmentQuestion' do
       aq = assessment_question_model(bank: AssessmentQuestionBank.create!(context: @course))
       aq.update_columns(root_account_id: nil)