Comment by dfajgljsldkjag 4 days ago
I have fixed many broken systems that used redis for small tasks. It is much better to put the jobs in the database we already have. This makes the code easier to manage and we have fewer things to worry about. I hope more teams start doing this to save time.
The way that Oban for Elixir and GoodJob for Ruby leverage PostgreSQL allows for very high throughput. It's not something that easily ports to other DBs.
A combination of LISTEN/NOTIFY for instantaneous reactivity, letting you get away with just periodic polling, and FOR UPDATE...SKIP LOCKED making it efficient and safe for parallel workers to grab tasks without co-ordination. It's actually covered in the article near the bottom there.
Good Job is a strong attempt. I believe it's based around Advisory Locks though.
Transactions around fetching/updating aren't trivial, that's true. However, the work that you're doing _is_ regular activity because it's part of your application logic. That's data about the state of your overall system and it is extremely helpful for it to stay with the app (not to mention how nice it makes testing).
Regarding overall throughput, we've written about running one million jobs a minute [1] on a single queue, and there are numerous companies running hundreds of millions of jobs a day with oban/postgres.
[1]: https://oban.pro/articles/one-million-jobs-a-minute-with-oba...
Appreciate the response, I'm learning some new things about the modern listening mechanisms for DBs which unlock more than I believed was possible.
For your first point - I would counter that a lot of data about my systems lives outside of the primary database. There is however an argument for adding a dependency, and for testing complexities. These are by and large solved problems at the scale I work with (not huge, not tiny).
I think both approaches work and I honestly just appreciate you guys holding Celery to task ;)
In Rails at least,aside from being used for background processing, redis gives you more goodies. You can store temporary state for tasks that require coordination between multiple nodes without race conditions, cache things to take some load off your DB, etc.
Besides, DB has higher likehood of failing you if you reach certain throughputs
Traditional DBs are a poor fit for high-throughput job systems in my experience. The transactions alone around fetching/updating jobs is non-trivial and can dwarf regular data activity in your system. Especially for monoliths which Python and Ruby apps by and large still are.
Personally I've migrated 3 apps _from_ DB-backed job queues _to_ Redis/other-backed systems with great success.