presto-main/src/main/java/io/prestosql/execution/TaskId.java/TaskId/TaskId
class TaskId:    public TaskId(StageId stageId, int id)
    {
        checkArgument(id >= 0, "id is negative");
        this.fullId = stageId.getQueryId().getId() + "." + stageId.getId() + "." + id;
    }