Redis cart persister

INFO

This document represents an architecture decision record (ADR) and has been mirrored from the ADR section in our Shopware 6 repository. You can find the original version here

With the last benchmarks it became clear how cost intensive the loading and saving of the shopping cart to and from the database is. A detailed analysis revealed two problems:

1. Every time the shopping cart is loaded, it is written back to the database after validation. However, this leads to a write on the connection which causes us to lose support for master-slave database setups.
2. To ensure the best possible performance, the shopping cart is written to the database as a serialized object. However, this in turn leads to rather high amounts of data having to be sent through the internal network.

To solve these problems, we implemented the Shopware\Core\Checkout\Cart\RedisCartPersister:

<?php declare(strict_types=1);

namespace Shopware\Core\Checkout\Cart;

class RedisCartPersister extends AbstractCartPersister
{
    /**
     * @var \Redis|\RedisCluster
     */
    private $redis;

    private EventDispatcherInterface $eventDispatcher;

    private bool $compress;

    public function load(string $token, SalesChannelContext $context): Cart {}

    public function save(Cart $cart, SalesChannelContext $context): void {}

    public function delete(string $token, SalesChannelContext $context): void {}

    public function replace(string $oldToken, string $newToken, SalesChannelContext $context): void {}
}

This stores the cart inside redis, which can be configured via the config in config/packages/*.yaml:

shopware:
    cart:
        redis_url: 'redis://redis'

If no redis connection is configured, the redis cart persister is removed from the DI container. This is done inside the \Shopware\Core\Checkout\DependencyInjection\CompilerPass\CartRedisCompilerPass:

<?php declare(strict_types=1);

namespace Shopware\Core\Checkout\DependencyInjection\CompilerPass;

class CartRedisCompilerPass implements CompilerPassInterface
{
    public function process(ContainerBuilder $container): void
    {
        if (!$container->getParameter('shopware.cart.redis_url')) {
            $container->removeDefinition('shopware.cart.redis');
            $container->removeDefinition(RedisCartPersister::class);

            return;
        }

        $container->removeDefinition(CartPersister::class);
        $container->setAlias(CartPersister::class, RedisCartPersister::class);
    }
}

In addition, to reduce network traffic, we used cache compression, which significantly reduces the amount of data to be sent. However, the compression can be deactivated again via config/packages/*.yaml:

shopware:
    cart:
        compress: false

Notice: Currently there is no migration path to transfer shopping carts from one storage to the other.