[mike_hearn]

Inevitably some users will decide to poll every 60 seconds or whatever, because they have no idea when the work will be completed and because what they really want is "results ASAP but willing to tolerate latency to pay less". And then your servers are doing a ton of TLS negotiation, user authentication, request serving and database lookups, just to answer "not yet".

I think people are getting distracted by the idea of connections being somehow expensive. They aren't really compared to polling (unless the poll is genuinely very rare). A stateless request is expensive because you have to go back to your source of truth on every request (probably an expensive and hard to scale RDBMS), and you don't control how often the user makes such requests. CPU load is potentially unbounded and users don't pay unless you introduce pay-per-poll micropayments.

Compare that to an MQ design: the overhead is a single TCP connection and a bit of memory to map that connection to an internal queue. Whilst the work sits in the queue or is being processed, nothing is happening and there's no DB load. Overhead is a matter of bytes and in the event that you run out of RAM you can always kick users off at random and let them exponentially back off and retry (automatically - because the libraries handle this and make it transparent). Or just use swap, after all, latency is not that important.

[tsimionescu]

Nothing prevents, in principle, a long lived HTTP connection where the server only replies once the response is available (long polling). However, on the real internet, such long lived connections just don't work, for a large minority of users. There are numerous devices, typically close to the client, which kill "idle" connections. NAT gateways and stateful firewalls are some of the most common culprits.

So, you just can't rely on your customers being able to keep around a long connection.

Not to mention the numerous corporate environments in which it is hard to even open an outgoing connection which is not HTTPS or a handful of other known protocols.

[mike_hearn]

Well, as I've said several times on this thread, good MQ libraries know how to reopen connections automatically if they break, backoff, retry, connect to several endpoints and load balance between them and so on. All this is an abstraction layer higher than what HTTP provides, so problems HTTP long polling can have in consumer/mobile use cases isn't necessarily relevant. It's like files vs SQLite.

As for the general issue of connections, that's true for consumer use cases. B2B workloads have far fewer problems with that especially when running in the cloud. If your cloud gives you mobile-quality internet then you have a problem, but again, it's a problem a good MQ implementation will fix for you. Consider the "lessons from 500 million tokens" blog post the other day, in which the author mentioned repeatedly that they had to write their own try/catch/retry loops around every OpenAI call because their HTTP API was so flaky.

And again, if you are behind a nasty firewall then you might find your connection dying at any moment because OpenAI got classified as a hate speech site or something. The fix is to file the right tickets to get your environment set up correctly.