wp_tinvwl_lists – too many records

We’ve been using the plugin for some years now. Recently the site ran into a lot of memory issues. I investigated what was going on and I noticed that the wp_tinvwl_lists table contained over a million records. I then looked at the code of the plugin and saw a heavy piece of code:

function unique_share_key()
	{
		global $wpdb;

		$sharekeys = $wpdb->get_results("SELECT <code>share_key</code> FROM <code>{$this->table}</code>", ARRAY_A); // WPCS: db call ok; no-cache ok; unprepared SQL ok.
		$share_keys = array();
		foreach ($sharekeys as $sharekey) {
			$share_keys[] = $sharekey['share_key'];
		}
		$new_key = '';
		do {
			$new_key = substr(md5(date('r') . mt_rand(0, 3000)), 0, 6);
		} while (array_search($new_key, $share_keys)); // @codingStandardsIgnoreLine WordPress.PHP.StrictInArray.MissingTrueStrict

		return $new_key;
	}

I think this function should be rewritten to be less heavy, something like this:

function unique_share_key()
{
    global $wpdb;

    $test_key = uniqid();
    $unique = false;
    while ($unique === false) {
        $unique = !$wpdb->get_var($wpdb->prepare("SELECT ID FROM <code>{$this->table}</code> WHERE share_key = %s", $test_key));
        $test_key = uniqid();
    }

    return $test_key;
}