add if_not_exists option to add_index

and use it in recent non-transactional migrations

Change-Id: Ie96e3cbf727403c5dfe9d04bc3403170c076d5b6
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/239560
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/postgresql_adapter.rb

@@ -181,26 +181,29 @@ module PostgreSQLAdapterExtensions
 
   def add_index(table_name, column_name, options = {})
     # catch a concurrent index add that fails because it already exists, and is invalid
-    if options[:algorithm] == :concurrently
+    if options[:algorithm] == :concurrently || options[:if_not_exists]
       column_names = index_column_names(column_name)
       index_name = options[:name].to_s if options.key?(:name)
       index_name ||= index_name(table_name, column_names)
 
       schema = shard.name if use_qualified_names?
 
-      exists = exec_query(<<-SQL, 'SCHEMA').rows.first[0].to_i > 0
-            SELECT COUNT(*)
+      valid = select_value(<<-SQL, 'SCHEMA')
+            SELECT indisvalid
             FROM pg_class t
             INNER JOIN pg_index d ON t.oid = d.indrelid
             INNER JOIN pg_class i ON d.indexrelid = i.oid
             WHERE i.relkind = 'i'
               AND i.relname = '#{index_name}'
               AND t.relname = '#{table_name}'
-              AND NOT indisvalid
               AND i.relnamespace IN (SELECT oid FROM pg_namespace WHERE nspname = #{schema ? "'#{schema}'" : 'ANY (current_schemas(false))'} )
+            LIMIT 1
       SQL
-      remove_index(table_name, name: index_name, algorithm: :concurrently) if exists
+      remove_index(table_name, name: index_name, algorithm: :concurrently) if valid == false && options[:algorithm] == :concurrently
+      return if options[:if_not_exists] && valid == true
     end
+    # CANVAS_RAILS6_1: can stop doing this in Rails 6.2, when it's natively supported
+    options.delete(:if_not_exists)
     super
   end
 

db/migrate/20200312144536_add_root_account_id_to_wikis.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToWikis < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :wikis, :root_account_id, :accounts, if_not_exists: true
-    add_index :wikis, :root_account_id, algorithm: :concurrently
+    add_index :wikis, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200312145819_add_root_account_id_to_wiki_pages.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToWikiPages < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :wiki_pages, :root_account_id, :accounts, if_not_exists: true
-    add_index :wiki_pages, :root_account_id, algorithm: :concurrently
+    add_index :wiki_pages, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200312150545_add_root_account_id_to_rubrics.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToRubrics < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :rubrics, :root_account_id, :accounts, if_not_exists: true
-    add_index :rubrics, :root_account_id, algorithm: :concurrently
+    add_index :rubrics, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200312152659_add_root_account_id_to_rubric_associations.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToRubricAssociations < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :rubric_associations, :root_account_id, :accounts, if_not_exists: true
-    add_index :rubric_associations, :root_account_id, algorithm: :concurrently
+    add_index :rubric_associations, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200312160431_add_root_account_id_to_rubric_assessments.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToRubricAssessments < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :rubric_assessments, :root_account_id, :accounts, if_not_exists: true
-    add_index :rubric_assessments, :root_account_id, algorithm: :concurrently
+    add_index :rubric_assessments, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200312161329_add_root_account_id_to_master_courses_migration_results.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToMasterCoursesMigrationResults < ActiveRecord::Migration[
 
   def up
     add_column_and_fk :master_courses_migration_results, :root_account_id, :accounts, if_not_exists: true
-    add_index :master_courses_migration_results, :root_account_id, algorithm: :concurrently
+    add_index :master_courses_migration_results, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200312202907_add_root_account_id_to_master_courses_master_templates.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToMasterCoursesMasterTemplates < ActiveRecord::Migration[5
 
   def up
     add_column_and_fk :master_courses_master_templates, :root_account_id, :accounts, if_not_exists: true
-    add_index :master_courses_master_templates, :root_account_id, algorithm: :concurrently
+    add_index :master_courses_master_templates, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200312205938_add_root_account_id_to_master_courses_master_content_tags.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToMasterCoursesMasterContentTags < ActiveRecord::Migration
 
   def up
     add_column_and_fk :master_courses_master_content_tags, :root_account_id, :accounts, if_not_exists: true
-    add_index :master_courses_master_content_tags, :root_account_id, algorithm: :concurrently
+    add_index :master_courses_master_content_tags, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200323182848_add_root_account_id_to_quizzes.rb

@@ -22,7 +22,7 @@ class AddRootAccountIdToQuizzes < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :quizzes, :root_account_id, :accounts, if_not_exists: true
-    add_index :quizzes, :root_account_id, algorithm: :concurrently
+    add_index :quizzes, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200323185224_add_root_account_id_to_quiz_questions.rb

@@ -22,7 +22,7 @@ class AddRootAccountIdToQuizQuestions < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :quiz_questions, :root_account_id, :accounts, if_not_exists: true
-    add_index :quiz_questions, :root_account_id, algorithm: :concurrently
+    add_index :quiz_questions, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200323185942_add_root_account_id_to_quiz_groups.rb

@@ -22,7 +22,7 @@ class AddRootAccountIdToQuizGroups < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :quiz_groups, :root_account_id, :accounts, if_not_exists: true
-    add_index :quiz_groups, :root_account_id, algorithm: :concurrently
+    add_index :quiz_groups, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200323190438_add_root_account_id_to_quiz_submissions.rb

@@ -22,7 +22,7 @@ class AddRootAccountIdToQuizSubmissions < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :quiz_submissions, :root_account_id, :accounts, if_not_exists: true
-    add_index :quiz_submissions, :root_account_id, algorithm: :concurrently
+    add_index :quiz_submissions, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200323190857_add_root_account_id_to_assessment_question_banks.rb

@@ -22,7 +22,7 @@ class AddRootAccountIdToAssessmentQuestionBanks < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :assessment_question_banks, :root_account_id, :accounts, if_not_exists: true
-    add_index :assessment_question_banks, :root_account_id, algorithm: :concurrently
+    add_index :assessment_question_banks, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200323191645_add_root_account_id_to_assessment_questions.rb

@@ -22,7 +22,7 @@ class AddRootAccountIdToAssessmentQuestions < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :assessment_questions, :root_account_id, :accounts, if_not_exists: true
-    add_index :assessment_questions, :root_account_id, algorithm: :concurrently
+    add_index :assessment_questions, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200408175631_add_root_account_id_to_master_courses_child_subscriptions.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToMasterCoursesChildSubscriptions < ActiveRecord::Migratio
 
   def up
     add_column_and_fk :master_courses_child_subscriptions, :root_account_id, :accounts, if_not_exists: true
-    add_index :master_courses_child_subscriptions, :root_account_id, algorithm: :concurrently
+    add_index :master_courses_child_subscriptions, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200409165445_add_root_account_id_to_content_tags.rb

@@ -22,7 +22,7 @@ class AddRootAccountIdToContentTags < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :content_tags, :root_account_id, :accounts, if_not_exists: true
-    add_index :content_tags, :root_account_id, algorithm: :concurrently
+    add_index :content_tags, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200409175218_add_root_account_id_to_developer_key_account_bindings.rb

@@ -22,7 +22,7 @@ class AddRootAccountIdToDeveloperKeyAccountBindings < ActiveRecord::Migration[5.
 
   def up
     add_column_and_fk :developer_key_account_bindings, :root_account_id, :accounts, if_not_exists: true
-    add_index :developer_key_account_bindings, :root_account_id, algorithm: :concurrently
+    add_index :developer_key_account_bindings, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200409180139_add_root_account_id_to_developer_keys.rb

@@ -22,7 +22,7 @@ class AddRootAccountIdToDeveloperKeys < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :developer_keys, :root_account_id, :accounts, if_not_exists: true
-    add_index :developer_keys, :root_account_id, algorithm: :concurrently
+    add_index :developer_keys, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200409181019_add_root_account_id_to_lti_resource_links.rb

@@ -22,7 +22,7 @@ class AddRootAccountIdToLtiResourceLinks < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :lti_resource_links, :root_account_id, :accounts, if_not_exists: true
-    add_index :lti_resource_links, :root_account_id, algorithm: :concurrently
+    add_index :lti_resource_links, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200409181832_add_root_account_id_to_lti_results.rb

@@ -22,7 +22,7 @@ class AddRootAccountIdToLtiResults < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :lti_results, :root_account_id, :accounts, if_not_exists: true
-    add_index :lti_results, :root_account_id, algorithm: :concurrently
+    add_index :lti_results, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200409182555_add_root_account_id_to_originality_reports.rb

@@ -22,7 +22,7 @@ class AddRootAccountIdToOriginalityReports < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :originality_reports, :root_account_id, :accounts, if_not_exists: true
-    add_index :originality_reports, :root_account_id, algorithm: :concurrently
+    add_index :originality_reports, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200410144107_add_root_account_id_to_master_courses_child_content_tags.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToMasterCoursesChildContentTags < ActiveRecord::Migration[
 
   def up
     add_column_and_fk :master_courses_child_content_tags, :root_account_id, :accounts, if_not_exists: true
-    add_index :master_courses_child_content_tags, :root_account_id, algorithm: :concurrently
+    add_index :master_courses_child_content_tags, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200410145235_add_root_account_id_to_discussion_topic_participants.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToDiscussionTopicParticipants < ActiveRecord::Migration[5.
 
   def up
     add_column_and_fk :discussion_topic_participants, :root_account_id, :accounts, if_not_exists: true
-    add_index :discussion_topic_participants, :root_account_id, algorithm: :concurrently
+    add_index :discussion_topic_participants, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200410151621_add_root_account_id_to_course_account_associations.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToCourseAccountAssociations < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :course_account_associations, :root_account_id, :accounts, if_not_exists: true
-    add_index :course_account_associations, :root_account_id, algorithm: :concurrently
+    add_index :course_account_associations, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200410152841_add_root_account_id_to_context_modules.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToContextModules < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :context_modules, :root_account_id, :accounts, if_not_exists: true
-    add_index :context_modules, :root_account_id, algorithm: :concurrently
+    add_index :context_modules, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200410153820_add_root_account_id_to_context_module_progressions.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToContextModuleProgressions < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :context_module_progressions, :root_account_id, :accounts, if_not_exists: true
-    add_index :context_module_progressions, :root_account_id, algorithm: :concurrently
+    add_index :context_module_progressions, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200410155410_add_root_account_id_to_content_participations.rb

@@ -22,6 +22,6 @@ class AddRootAccountIdToContentParticipations < ActiveRecord::Migration[5.2]
   def change
     add_column :content_participations, :root_account_id, :integer, limit: 8
     add_foreign_key :content_participations, :accounts, column: :root_account_id
-    add_index :content_participations, :root_account_id, algorithm: :concurrently
+    add_index :content_participations, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 end

db/migrate/20200410160448_add_root_account_id_to_content_participation_counts.rb

@@ -22,6 +22,6 @@ class AddRootAccountIdToContentParticipationCounts < ActiveRecord::Migration[5.2
   def change
     add_column :content_participation_counts, :root_account_id, :integer, limit: 8
     add_foreign_key :content_participation_counts, :accounts, column: :root_account_id
-    add_index :content_participation_counts, :root_account_id, algorithm: :concurrently
+    add_index :content_participation_counts, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 end

db/migrate/20200410200857_add_root_account_id_index_to_lti_line_items.rb

@@ -20,6 +20,6 @@ class AddRootAccountIdIndexToLtiLineItems < ActiveRecord::Migration[5.2]
   disable_ddl_transaction!
 
   def change
-    add_index :lti_line_items, :root_account_id, algorithm: :concurrently
+    add_index :lti_line_items, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 end

db/migrate/20200413153758_add_root_account_id_to_content_migrations.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToContentMigrations < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :content_migrations, :root_account_id, :accounts, if_not_exists: true
-    add_index :content_migrations, :root_account_id, algorithm: :concurrently
+    add_index :content_migrations, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200421145054_add_root_account_id_to_attachment_associations.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToAttachmentAssociations < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :attachment_associations, :root_account_id, :accounts, if_not_exists: true
-    add_index :attachment_associations, :root_account_id, algorithm: :concurrently
+    add_index :attachment_associations, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200421163756_add_root_account_id_to_assignment_override_students.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToAssignmentOverrideStudents < ActiveRecord::Migration[5.2
 
   def up
     add_column_and_fk :assignment_override_students, :root_account_id, :accounts, if_not_exists: true
-    add_index :assignment_override_students, :root_account_id, algorithm: :concurrently
+    add_index :assignment_override_students, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200421165055_add_root_account_id_to_assignment_overrides.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToAssignmentOverrides < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :assignment_overrides, :root_account_id, :accounts, if_not_exists: true
-    add_index :assignment_overrides, :root_account_id, algorithm: :concurrently
+    add_index :assignment_overrides, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200421174956_add_root_account_id_to_assignment_groups.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToAssignmentGroups < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :assignment_groups, :root_account_id, :accounts, if_not_exists: true
-    add_index :assignment_groups, :root_account_id, algorithm: :concurrently
+    add_index :assignment_groups, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200423155711_add_root_account_id_to_score_statistics.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToScoreStatistics < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :score_statistics, :root_account_id, :accounts, if_not_exists: true
-    add_index :score_statistics, :root_account_id, algorithm: :concurrently
+    add_index :score_statistics, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200423160434_add_root_account_id_to_scores.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToScores < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :scores, :root_account_id, :accounts, if_not_exists: true
-    add_index :scores, :root_account_id, algorithm: :concurrently
+    add_index :scores, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200423161237_add_root_account_id_to_grading_periods.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToGradingPeriods < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :grading_periods, :root_account_id, :accounts, if_not_exists: true
-    add_index :grading_periods, :root_account_id, algorithm: :concurrently
+    add_index :grading_periods, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200424153715_add_root_account_id_to_post_policies.rb

@@ -24,7 +24,7 @@ class AddRootAccountIdToPostPolicies < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :post_policies, :root_account_id, :accounts, if_not_exists: true
-    add_index :post_policies, :root_account_id, algorithm: :concurrently
+    add_index :post_policies, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200424155029_add_root_account_id_to_late_policies.rb

@@ -24,7 +24,7 @@ class AddRootAccountIdToLatePolicies < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :late_policies, :root_account_id, :accounts, if_not_exists: true
-    add_index :late_policies, :root_account_id, algorithm: :concurrently
+    add_index :late_policies, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200424160852_add_root_account_id_to_grading_standards.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToGradingStandards < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :grading_standards, :root_account_id, :accounts, if_not_exists: true
-    add_index :grading_standards, :root_account_id, algorithm: :concurrently
+    add_index :grading_standards, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200424161556_add_root_account_id_to_custom_gradebook_columns.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToCustomGradebookColumns < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :custom_gradebook_columns, :root_account_id, :accounts, if_not_exists: true
-    add_index :custom_gradebook_columns, :root_account_id, algorithm: :concurrently
+    add_index :custom_gradebook_columns, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200424164435_add_root_account_id_to_learning_outcome_group.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToLearningOutcomeGroup < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :learning_outcome_groups, :root_account_id, :accounts, if_not_exists: true
-    add_index :learning_outcome_groups, :root_account_id, algorithm: :concurrently
+    add_index :learning_outcome_groups, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200424170933_add_root_account_id_to_custom_gradebook_column_data.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToCustomGradebookColumnData < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :custom_gradebook_column_data, :root_account_id, :accounts, if_not_exists: true
-    add_index :custom_gradebook_column_data, :root_account_id, algorithm: :concurrently
+    add_index :custom_gradebook_column_data, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200424200625_add_root_account_id_to_conversations.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToConversations < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :conversations, :root_account_id, :accounts, if_not_exists: true
-    add_index :conversations, :root_account_id, algorithm: :concurrently
+    add_index :conversations, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200424201444_add_root_account_id_to_conversation_participants.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToConversationParticipants < ActiveRecord::Migration[5.2]
 
     def up
     add_column_and_fk :conversation_participants, :root_account_id, :accounts, if_not_exists: true
-    add_index :conversation_participants, :root_account_id, algorithm: :concurrently
+    add_index :conversation_participants, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200427144325_add_root_account_id_to_master_courses_master_migrations.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToMasterCoursesMasterMigrations < ActiveRecord::Migration[
 
   def up
     add_column_and_fk :master_courses_master_migrations, :root_account_id, :accounts, if_not_exists: true
-    add_index :master_courses_master_migrations, :root_account_id, algorithm: :concurrently
+    add_index :master_courses_master_migrations, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200427155044_add_root_account_id_to_learning_outcomes.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToLearningOutcomes < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :learning_outcomes, :root_account_id, :accounts, if_not_exists: true
-    add_index :learning_outcomes, :root_account_id, algorithm: :concurrently
+    add_index :learning_outcomes, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200427162315_add_root_account_id_to_learning_outcome_question_results.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToLearningOutcomeQuestionResults < ActiveRecord::Migration
 
   def up
     add_column_and_fk :learning_outcome_question_results, :root_account_id, :accounts, if_not_exists: true
-    add_index :learning_outcome_question_results, :root_account_id, algorithm: :concurrently
+    add_index :learning_outcome_question_results, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200427162639_add_root_account_id_to_learning_outcome_results.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToLearningOutcomeResults < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :learning_outcome_results, :root_account_id, :accounts, if_not_exists: true
-    add_index :learning_outcome_results, :root_account_id, algorithm: :concurrently
+    add_index :learning_outcome_results, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200427163600_add_root_account_id_to_outcome_proficiencies.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToOutcomeProficiencies < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :outcome_proficiencies, :root_account_id, :accounts, if_not_exists: true
-    add_index :outcome_proficiencies, :root_account_id, algorithm: :concurrently
+    add_index :outcome_proficiencies, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200427183334_add_root_account_id_to_outcome_proficiency_ratings.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToOutcomeProficiencyRatings < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :outcome_proficiency_ratings, :root_account_id, :accounts, if_not_exists: true
-    add_index :outcome_proficiency_ratings, :root_account_id, algorithm: :concurrently
+    add_index :outcome_proficiency_ratings, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200429215549_add_root_account_id_to_account_users.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToAccountUsers < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :account_users, :root_account_id, :accounts, if_not_exists: true
-    add_index :account_users, :root_account_id, algorithm: :concurrently
+    add_index :account_users, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200429220808_add_root_account_id_to_enrollment_states.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToEnrollmentStates < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :enrollment_states, :root_account_id, :accounts, if_not_exists: true
-    add_index :enrollment_states, :root_account_id, algorithm: :concurrently
+    add_index :enrollment_states, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200429221128_add_root_account_id_to_group_memberships.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToGroupMemberships < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :group_memberships, :root_account_id, :accounts, if_not_exists: true
-    add_index :group_memberships, :root_account_id, algorithm: :concurrently
+    add_index :group_memberships, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200429221630_add_root_account_id_to_role_overrides.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToRoleOverrides < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :role_overrides, :root_account_id, :accounts, if_not_exists: true
-    add_index :role_overrides, :root_account_id, algorithm: :concurrently
+    add_index :role_overrides, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200429221913_add_root_account_id_to_access_tokens.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToAccessTokens < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :access_tokens, :root_account_id, :accounts, if_not_exists: true
-    add_index :access_tokens, :root_account_id, algorithm: :concurrently
+    add_index :access_tokens, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200429222840_add_root_account_id_to_user_account_associations.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToUserAccountAssociations < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :user_account_associations, :root_account_id, :accounts, if_not_exists: true
-    add_index :user_account_associations, :root_account_id, algorithm: :concurrently
+    add_index :user_account_associations, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200505150604_add_root_account_id_to_discussion_entries.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToDiscussionEntries < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :discussion_entries, :root_account_id, :accounts, if_not_exists: true
-    add_index :discussion_entries, :root_account_id, algorithm: :concurrently
+    add_index :discussion_entries, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200506171206_add_real_user_id_to_access_token.rb

@@ -23,7 +23,7 @@ class AddRealUserIdToAccessToken < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :access_tokens, :real_user_id, :users, if_not_exists: true
-    add_index :access_tokens, :real_user_id, algorithm: :concurrently, where: "real_user_id IS NOT NULL"
+    add_index :access_tokens, :real_user_id, algorithm: :concurrently, where: "real_user_id IS NOT NULL", if_not_exists: true
   end
 
   def down

db/migrate/20200511162846_add_root_account_id_to_asset_user_accesses.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToAssetUserAccesses < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :asset_user_accesses, :root_account_id, :accounts, if_not_exists: true
-    add_index :asset_user_accesses, :root_account_id, algorithm: :concurrently
+    add_index :asset_user_accesses, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200511181051_add_root_account_id_to_attachments.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToAttachments < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :attachments, :root_account_id, :accounts, if_not_exists: true
-    add_index :attachments, :root_account_id, algorithm: :concurrently
+    add_index :attachments, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200511181838_add_root_account_id_to_content_shares.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToContentShares < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :content_shares, :root_account_id, :accounts, if_not_exists: true
-    add_index :content_shares, :root_account_id, algorithm: :concurrently
+    add_index :content_shares, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200511182640_add_root_account_id_to_user_notes.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToUserNotes < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :user_notes, :root_account_id, :accounts, if_not_exists: true
-    add_index :user_notes, :root_account_id, algorithm: :concurrently
+    add_index :user_notes, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200511183830_add_root_account_id_to_calendar_events.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToCalendarEvents < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :calendar_events, :root_account_id, :accounts, if_not_exists: true
-    add_index :calendar_events, :root_account_id, algorithm: :concurrently
+    add_index :calendar_events, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200511184244_add_root_account_id_to_folders.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToFolders < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :folders, :root_account_id, :accounts, if_not_exists: true
-    add_index :folders, :root_account_id, algorithm: :concurrently
+    add_index :folders, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200511191833_add_root_account_id_to_communication_channels.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToCommunicationChannels < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :communication_channels, :root_account_id, :accounts, if_not_exists: true
-    add_index :communication_channels, :root_account_id, algorithm: :concurrently
+    add_index :communication_channels, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200511193351_add_root_account_id_to_conversation_messages.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToConversationMessages < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :conversation_messages, :root_account_id, :accounts, if_not_exists: true
-    add_index :conversation_messages, :root_account_id, algorithm: :concurrently
+    add_index :conversation_messages, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200511193610_add_root_account_id_to_conversation_message_participants.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToConversationMessageParticipants < ActiveRecord::Migratio
 
   def up
     add_column_and_fk :conversation_message_participants, :root_account_id, :accounts, if_not_exists: true
-    add_index :conversation_message_participants, :root_account_id, algorithm: :concurrently
+    add_index :conversation_message_participants, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200511193857_add_root_account_id_to_favorites.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToFavorites < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :favorites, :root_account_id, :accounts, if_not_exists: true
-    add_index :favorites, :root_account_id, algorithm: :concurrently
+    add_index :favorites, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200511194513_add_root_account_id_to_discussion_topics.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToDiscussionTopics < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :discussion_topics, :root_account_id, :accounts, if_not_exists: true
-    add_index :discussion_topics, :root_account_id, algorithm: :concurrently
+    add_index :discussion_topics, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200527195732_add_root_account_id_to_discussion_entry_participants.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToDiscussionEntryParticipants < ActiveRecord::Migration[5.
 
   def up
     add_column_and_fk :discussion_entry_participants, :root_account_id, :accounts, if_not_exists: true
-    add_index :discussion_entry_participants, :root_account_id, algorithm: :concurrently
+    add_index :discussion_entry_participants, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200528182340_add_root_account_id_to_web_conference_participants.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToWebConferenceParticipants < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :web_conference_participants, :root_account_id, :accounts, if_not_exists: true
-    add_index :web_conference_participants, :root_account_id, algorithm: :concurrently
+    add_index :web_conference_participants, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

db/migrate/20200528182917_add_root_account_id_to_web_conferences.rb

@@ -23,7 +23,7 @@ class AddRootAccountIdToWebConferences < ActiveRecord::Migration[5.2]
 
   def up
     add_column_and_fk :web_conferences, :root_account_id, :accounts, if_not_exists: true
-    add_index :web_conferences, :root_account_id, algorithm: :concurrently
+    add_index :web_conferences, :root_account_id, algorithm: :concurrently, if_not_exists: true
   end
 
   def down

spec/initializers/active_record_spec.rb

@@ -354,6 +354,10 @@ module ActiveRecord
         User.connection.alter_constraint(:user_services, old_name, new_name: 'test')
         expect(User.connection.find_foreign_key(:user_services, :users)).to eq 'test'
       end
+
+      it "allows if_not_exists on add_index" do
+        expect { User.connection.add_index(:enrollments, :user_id, if_not_exists: true) }.not_to raise_exception
+      end
     end
   end
 end