Asynchronous Communication: Offload expensive operations to your message queues

Asynchronous Communication Explained !!

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Asynchronous workflows help reduce request times for expensive operations that would otherwise be performed in-line. They can also help by doing time-consuming work in advance, such as periodic aggregation of data.

Message queues

Message queues receive, hold, and deliver messages. If an operation is too slow to perform inline, you can use a message queue with the following workflow:

  • An application publishes a job to the queue, then notifies the user of job status
  • A worker picks up the job from the queue, processes it, then signals the job is complete

The user is not blocked and the job is processed in the background. During this time, the client might optionally do a small amount of processing to make it seem like the task has completed. For example, if posting a tweet, the tweet could be instantly posted to your timeline, but it could take some time before your tweet is actually delivered to all of your followers.

Redis is useful as a simple message broker but messages can be lost.

RabbitMQ is popular but requires you to adapt to the 'AMQP' protocol and manage your own nodes.

Amazon SQS is hosted but can have high latency and has the possibility of messages being delivered twice.

Task queues

Tasks queues receive tasks and their related data, runs them, then delivers their results. They can support scheduling and can be used to run computationally-intensive jobs in the background.

Celery has support for scheduling and primarily has python support.

Back pressure

If queues start to grow significantly, the queue size can become larger than memory, resulting in cache misses, disk reads, and even slower performance. Back pressure can help by limiting the queue size, thereby maintaining a high throughput rate and good response times for jobs already in the queue. Once the queue fills up, clients get a server busy or HTTP 503 status code to try again later. Clients can retry the request at a later time, perhaps with exponential backoff.

Points to Consider:

  • Use cases such as inexpensive calculations and realtime workflows might be better suited for synchronous operations, as introducing queues can add delays and complexity.

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Aniket Joshi's photo

Overall, i liked this post, good, decent starter info on asynchronous processing. But, it would/could have been helpful if you could have spent some more time on describing the issues with synchronous processing, and when to move to async.

vishnu chilamakuru's photo

Hey thanks for the feedback.. The post already talks about advantages of asynchronous communication and when to use it over synchronous communication.

  • If any task is time consuming and makes the user wait for more time it's best suitable candidate for asynchronous communication.
  • Also, another point to consider is the acceptable delay of the task. Ex: If some celebrity you follow tweets a a follower it is ok to see that in your timeline after some delay like few seconds or minutes. So some level of delay is acceptable in user behavior here.
Suraj Shende's photo

The first reading is done. Maybe I will read it again... 🙃