presto-main/src/main/java/io/prestosql/execution/SqlTask.java/TaskHolder/getIoStats
class TaskHolder:        public SqlTaskIoStats getIoStats()
        {
            // if we are finished, return the final IoStats
            if (finalIoStats != null) {
                return finalIoStats;
            }
            // if we haven't started yet, return an empty IoStats
            if (taskExecution == null) {
                return new SqlTaskIoStats();
            }
            // get IoStats from the current task execution
            TaskContext taskContext = taskExecution.getTaskContext();
            return new SqlTaskIoStats(taskContext.getProcessedInputDataSize(), taskContext.getInputPositions(), taskContext.getOutputDataSize(), taskContext.getOutputPositions());
        }