Large Collection Exhausting Memory

Question

I am writing an admin module. I created a collection and if the number of rows in the table are small it loads fine. Ultimately the table will have 250k rows in it and when I attempt to load the collection it exhausts memory. I was under the impression that Magento would lazy load collections. I also will probably need to know how to use the resource iterator in mage 2 as well. I can provide code samples but there is little more than a basic module skeleton at this point. I would greatly appreciate a code example of how to handle and iterate through a large collection.

Note: the collection is pulling from a custom table

Controller:

<?php
namespace Customer\Customerimportexport\Controller\Adminhtml\Import;

use Magento\Backend\App\Action;
use Magento\Backend\App\Action\Context;
use Customer\Customerimportexport\Model\WebcustomersFactory;

class Index extends \Magento\Backend\App\Action
{

    protected $_modelWebcustomersFactory;

    public function __construct(
        Context $context,
        WebcustomersFactory $modelWebcustomersFactory
    ) {
        parent::__construct($context);
        $this->_modelWebcustomersFactory = $modelWebcustomersFactory;
    }

    public function execute()
    {

        $webcustomersModel = $this->_modelWebcustomersFactory->create();

        // Get webcustomers collection
        $webcustomersCollection = $webcustomersModel->getCollection();

        // Load all data of collection
        foreach ($webcustomersModel->getCollection() as $key => $webcustomer) {
            var_dump($webcustomer->getData());
            die();
        }

        $this->_view->loadLayout();
        $this->_view->renderLayout();
    }

}

Model

<?php

namespace Customer\Customerimportexport\Model;

use \Magento\Framework\Model\AbstractModel;

class Webcustomers extends AbstractModel
{
    /**
     * Define resource model
     */
    protected function _construct()
    {
        $this->_init('Customer\Customerimportexport\Model\ResourceModel\Webcustomers');
    }
}

Resource Model

<?php

namespace Customer\Customerimportexport\Model\ResourceModel;

class Webcustomers extends \Magento\Framework\Model\ResourceModel\Db\AbstractDb
{
    /**
     * Define main table
     */
    protected function _construct()
    {
        $this->_init('web_customers', 'entity_id');
    }
}

Collection

<?php 

namespace Customer\Customerimportexport\Model\ResourceModel\Webcustomers;

use \Magento\Framework\Model\Resource\Db\Collection\AbstractCollection;

class Collection extends \Magento\Framework\Model\ResourceModel\Db\Collection\AbstractCollection
{
    /**
     * Define model & resource model
     */
    protected function _construct()
    {
        $this->_init(
            'Customer\Customerimportexport\Model\Webcustomers',
            'Customer\Customerimportexport\Model\ResourceModel\Webcustomers'
        );
    }
}

Answer 1

This is probably your culprit: var_dump($webcustomersCollection->count());

That loads the entire collection (of all records in the table) to get the count. The loop does the same thing.

Apply some filters to your collection before looping.

There is some more that needs to be cleaned up with this code, (dependency injection, rendering output, etc.), but that's an answer for a different question.