presto-main/src/main/java/io/prestosql/operator/RowNumberOperator.java/RowNumberOperator/updateMemoryReservation
class RowNumberOperator:    private boolean updateMemoryReservation()
    {
        // Operator/driver will be blocked on memory after we call localUserMemoryContext.setBytes().
        // If memory is not available, once we return, this operator will be blocked until memory is available.
        long memorySizeInBytes = groupByHash.map(GroupByHash::getEstimatedSize).orElse(0L) + partitionRowCount.sizeOf();
        localUserMemoryContext.setBytes(memorySizeInBytes);
        // If memory is not available, inform the caller that we cannot proceed for allocation.
        return operatorContext.isWaitingForMemory().isDone();
    }