presto-main/src/main/java/io/prestosql/execution/StageId.java/StageId/valueOf
class StageId:    public static StageId valueOf(List<String> ids)
    {
        checkArgument(ids.size() == 2, "Expected two ids but got: %s", ids);
        return new StageId(new QueryId(ids.get(0)), Integer.parseInt(ids.get(1)));
    }