presto-main/src/main/java/io/prestosql/dispatcher/LocalDispatchQuery.java/LocalDispatchQuery/getUserMemoryReservation
class LocalDispatchQuery:    @Override
    public DataSize getUserMemoryReservation()
    {
        return tryGetQueryExecution()
                .map(QueryExecution::getUserMemoryReservation)
                .orElseGet(() -> new DataSize(0, BYTE));
    }