Cleanup PopulateUserHighestRoles bg migration

Execute potential remaining jobs for the user_highest_roles population
inline and remove the temporary index for it.

changelogs/unreleased/cleanup_user_highest_roles_background_migration.yml

+---
+title: Cleanup background migration for populating user_highest_roles table
+merge_request: 31218
+author:
+type: other

db/post_migrate/20200506125731_cleanup_user_highest_roles_population.rb

+# frozen_string_literal: true
+
+class CleanupUserHighestRolesPopulation < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  INDEX_NAME = 'index_for_migrating_user_highest_roles_table'
+
+  disable_ddl_transaction!
+
+  def up
+    Gitlab::BackgroundMigration.steal('PopulateUserHighestRolesTable')
+
+    remove_concurrent_index(:users, :id, name: INDEX_NAME)
+  end
+
+  def down
+    add_concurrent_index(:users,
+                         :id,
+                         where: "state = 'active' AND user_type IS NULL AND bot_type IS NULL AND ghost IS NOT TRUE",
+                         name: INDEX_NAME)
+  end
+end

db/structure.sql

@@ -9556,8 +9556,6 @@ CREATE UNIQUE INDEX index_feature_gates_on_feature_key_and_key_and_value ON publ
 
 CREATE UNIQUE INDEX index_features_on_key ON public.features USING btree (key);
 
-CREATE INDEX index_for_migrating_user_highest_roles_table ON public.users USING btree (id) WHERE (((state)::text = 'active'::text) AND (user_type IS NULL) AND (bot_type IS NULL) AND (ghost IS NOT TRUE));
-
 CREATE INDEX index_for_resource_group ON public.ci_builds USING btree (resource_group_id, id) WHERE (resource_group_id IS NOT NULL);
 
 CREATE INDEX index_for_status_per_branch_per_project ON public.merge_trains USING btree (target_project_id, target_branch, status);
@@ -13709,5 +13707,6 @@ COPY "schema_migrations" (version) FROM STDIN;
 20200429181335
 20200429181955
 20200429182245
+20200506125731
 \.