Downloading hude amounts of data from DB via PHP

This set of classes will help you to implement iterative creation of files with huge amount of data from database.

First steps

First of all create class wich will fetch data, process it and contain some utility methods:

class HttpJob implements HttpJobInterface
{

    /
     * Amount of data to be processed per one iteration
     *
     * @var integer
     */
    protected $limit = 1;

    /
     * Processing data subset. In our case we store data in the CSV file
     * And if this file is not yet created, then create one
     */
    protected function process(array $data): void
    {
        if (! isset($_SESSION[$_POST['job-id']]['filename'])) {
            $_SESSION[$_POST['job-id']]['filename'] = md5(microtime(true)) . '.csv';
            // here we need to create file, because it is not exists yet
        }

        // and here we can store $data in the file with name $_SESSION[$_POST['job-id']]['filename']
    }

    /
     * This method returns a subset of required data
     For example SELECT FROM your_table WHERE %condition% LIMIT %start_index%, $this->limit
     */
    protected function getDataBulk(int $from, int $limit): array
    {
        return [
            // some testing data
        ];
    }

	/
	 *	This method calculates totoal amount of data
	 for example SELECT COUNT() FROM your_table WHERE %condition%
	 */
    protected function getDataAmount(): int
    {
        // here we use testing data, but you can fetch it from database
        global $testData;

        return count($testData);
    }
}