Update index on namespaces for type and id

Including the id column in the partial index improves performance.

changelogs/unreleased/209831-propagate-integrations-using-batching-and-queues.yml

+---
+title: Update database index on namespaces for type and id
+merge_request: 42128
+author:
+type: other

db/post_migrate/20200917165525_update_index_on_namespaces_for_type_and_id.rb

+# frozen_string_literal: true
+
+class UpdateIndexOnNamespacesForTypeAndId < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  disable_ddl_transaction!
+
+  OLD_INDEX_NAME = 'index_namespaces_on_type_partial'
+  NEW_INDEX_NAME = 'index_namespaces_on_type_and_id_partial'
+
+  def up
+    add_concurrent_index(:namespaces, [:type, :id], where: 'type IS NOT NULL', name: NEW_INDEX_NAME)
+
+    remove_concurrent_index_by_name(:namespaces, OLD_INDEX_NAME)
+  end
+
+  def down
+    add_concurrent_index(:namespaces, :type, where: 'type IS NOT NULL', name: OLD_INDEX_NAME)
+
+    remove_concurrent_index_by_name(:namespaces, NEW_INDEX_NAME)
+  end
+end

db/schema_migrations/20200917165525

+0080b9192ba5b4ea3853cfd930d58e10b9619f3d9a54016b574712e5ec2084f6
\ No newline at end of file

db/structure.sql

@@ -20596,7 +20596,7 @@ CREATE UNIQUE INDEX index_namespaces_on_runners_token_encrypted ON namespaces US
 
 CREATE INDEX index_namespaces_on_shared_and_extra_runners_minutes_limit ON namespaces USING btree (shared_runners_minutes_limit, extra_shared_runners_minutes_limit);
 
-CREATE INDEX index_namespaces_on_type_partial ON namespaces USING btree (type) WHERE (type IS NOT NULL);
+CREATE INDEX index_namespaces_on_type_and_id_partial ON namespaces USING btree (type, id) WHERE (type IS NOT NULL);
 
 CREATE INDEX index_non_requested_project_members_on_source_id_and_type ON members USING btree (source_id, source_type) WHERE ((requested_at IS NULL) AND ((type)::text = 'ProjectMember'::text));