[index] add index on status_revisions.status_id

db/migrate/20210102225500_add_index_on_status_revisions.rb

@@ -0,0 +1,7 @@
+class AddIndexOnStatusRevisions < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def change
+    add_index :status_revisions, :status_id, algorithm: :concurrently
+  end
+end