I am creating a script that creates a large number of random generated 10 character long Codes e.g. 5 million Codes. I insert my created Codes in batches of 10000 into a database to not run into trouble with memory.
Now i want to write all these 5 million Codes into a csv file to download but my memory gets exceeded when i try it

//batchsize of 10000
$size = 10000;
$group = [];

// generate 5 million Codes
for ($i = 1; $i <= 5000000; $i++) {
    $randomString = generateUniqueString($existingStrings);
    $group[] = $randomString;

    if (count($group) >= $size) {
        $db->beginTransaction();

        $db->insertCodes($group);

        $db->commitTransaction();

        $group = [];
    }
}

// Insert remaining codes in the last group
if (!empty($group)) {

    $db->beginTransaction();

    $db->insertCodes($group);

    $db->commitTransaction();
}

$handle = fopen($file, 'w');
// the problem probably occurs around here when everything gets stored in $result
$result = $db->getAllCodes();

// Write codes to the CSV file
while ($row = mysqli_fetch_assoc($result)) {
    fputcsv($handle, [$row['Code']]);
}

fclose($handle);
$db->close();

Do you have any idea how i am able to also insert them in batches without exceeding my memory maximum? I tried a few methods all not working and i am stuck at this point of my Code