<?php

use Magento\Framework\Model\ResourceModel\IteratorFactory;

class HugeTableIterator
{
    /** @var IteratorFactory */
    private $iteratorFactory;

    /** UnbufferedQueryConnectionFactory */
    private $unbufferedQueryConnectionFactory;

    public function __construct(
        IteratorFactory $iteratorFactory,
        UnbufferedQueryConnectionFactory $unbufferedQueryConnectionFactory
    ) {
        $this->iteratorFactory = $iteratorFactory;
        $this->unbufferedQueryConnectionFactory = $unbufferedQueryConnectionFactory
    }

    public function processResults(): void
    {
        $connection = $this->unbufferedQueryConnectionFactory->factory();
        $iterator = $this->iteratorFactory->create();

        $query = $connection->select()->from('huge_table');
        $iterator->walk((string) $query, [function (array $result) {
            // do something with $result
        }], [], $connection);
    }
}