The Consumer is too Fast

I was recently reviewing a PR moving a RabbitMQ task into a cronjob. This alone was a bit of a red flag, but the commit message piqued my interest.

Move request to cron the queue consumer is too fast Some requests send with the incorrect order status because the queue consumer is processing them before they are ready.

For context, this is a Magento 2 application and the consumer in question is responsible for sending orders to a backend system when it reaches the complete status. The PR under review was fixing a reported issue where some orders send with a processing status.

There isn’t a lot of magic to this process. If an order status changes to complete it is published to RabbitMQ.

Here is the actual logic controlling the publishing, edited for brevity. Orders should never be in the queue unless the order is complete.

if ($order->getState() === 'complete') {
    $this->publisher->publish(
        'our.queue',
        (int) $order->getEntityId()
    );
}

At this point I’m still convinced moving from the message queue to cron is not the ideal solution, but am very curious how orders are sending before reaching completion. Looking at the observer configuration I see the publish happens on the sales_order_save_after event.

This event fires before the transaction commits to the database and I’m pretty confident is causing a race condition. Changing the event to the sales_order_save_commit_after should fix our problem.