2022-03-25 - Initial state id loader

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

During the performance optimizations, it was noticed that the determination of the initial state, for a state machine, is currently associated with a quite high database load, although only one ID must be determined. This has the consequence that during the checkout unnecessarily much load on the database is caused, in order to determine the initial state id, because this must be determined for the order.state, order_delivery.state as well as the order_transaction.state machine. Responsible for the load were the \Shopware\Core\System\StateMachine\StateMachineRegistry::getInitialState method, which is usually used as follows:

$this->stateMachineRegistry->getInitialState(OrderStates::STATE_MACHINE, $context->getContext())->getId(),
//...
$this->stateMachineRegistry->getInitialState(OrderDeliveryStates::STATE_MACHINE, $context->getContext())->getId(),
//...
$this->stateMachineRegistry->getInitialState(OrderTransactionStates::STATE_MACHINE, $context->getContext())->getId(),
//...

Inside the getInitialState, the complete StateMachine object is loaded, including all transitions and their from and to states:

$criteria = new Criteria();
$criteria
    ->addFilter(new EqualsFilter('state_machine.technicalName', $name))
    ->setLimit(1);

$criteria->getAssociation('transitions')
    ->addSorting(new FieldSorting('state_machine_transition.actionName'))
    ->addAssociation('fromStateMachineState')
    ->addAssociation('toStateMachineState');

$criteria->getAssociation('states')
    ->addSorting(new FieldSorting('state_machine_state.technicalName'));

Since this means unnecessary load for the database, we have @deprecated this method for v6.5.0.0 and provided a new smaller and faster service. Furthermore, all usages in the core have been removed and replaced with the new service:

<?php declare(strict_types=1);

namespace Shopware\Core\System\StateMachine\Loader;

class InitialStateIdLoader implements ResetInterface
{
    public const CACHE_KEY = 'state-machine-initial-state-ids';

    public function get(string $name): string
    {
        if (isset($this->ids[$name])) {
            return $this->ids[$name];
        }

        $this->ids = $this->load();

        return $this->ids[$name];
    }

    private function load(): array
    {
        return $this->cache->get(self::CACHE_KEY, function () {
            return $this->connection->fetchAllKeyValue(
                'SELECT technical_name, LOWER(HEX(`initial_state_id`)) as initial_state_id FROM state_machine'
            );
        });
    }
}

With the help of this service we were able to reduce the determination of the initial state under load by a multiple. The cache shown here is invalidated by a DAL written event on the state_machine entity.