presto-main/src/main/java/io/prestosql/execution/QueryStateMachine.java/QueryOutputManager/getQueryOutputInfo
class QueryOutputManager:        private synchronized Optional<QueryOutputInfo> getQueryOutputInfo()
        {
            if (columnNames == null || columnTypes == null) {
                return Optional.empty();
            }
            return Optional.of(new QueryOutputInfo(columnNames, columnTypes, exchangeLocations, noMoreExchangeLocations));
        }