You're applying generic heuristics against a problem where folks have specific domain knowledge that contradicts those heuristics.
I cannot stress this enough; you are flat wrong if you think Postgres is appropriate to use for queueing.
If you already have tooling and knowledge for managing Postgres, and Postgres is sufficient for your queueing needs, then why would you incur the cost of introducing a new service? Most situations don't require the best tool for the job, and in that case, you are well served to use a tool you already have.
If you are using an abstraction layer over your queues (you almost certainly are) then you should be able to easily change to a different queue implementation later, should the need arise.
So if my language doesn't have a library like Que ( no thanks using Ruby ) I can't do anything with PG whereas using Redis or any other solution you can use "subscribe" / "publish" ect ...
This has nothing to do with getting shit done, and everything to do with people who don't want to learn new things because they're afraid of not being smart enough to make the new thing work.
If a PG-based solution meets the needs then this reduces complexity in the large. And this has nothing to do with learning or not learning.
Sorry but your argument just does not hold up.
The only argument that doesn't hold up is "use one tool for everything". This ideology is for lazy people who want to anchor themselves in a period of time, and refuse to learn new things.
Agree on devops. Of course.
There’s still the security surface area argument and the overall complexity argument—complexity of the system of systems is NOT reduced by adding technologies.
By way of analogy, using military aircraft, take the F35 vs. the A-10. The F35 is insanely more complex than the nearly indestructible A10 in large part due to the massive number of subsystems, software, sensors, etc. Sure the F35 way more capable (this is NOT a head to head argument about the military capabilities or said aircraft) than the A10, but it also has orders of magnitude more failure modes. More parts. More complexity. More opportunities for failure. This is engineering fact.
What's frustrating about this conversation is that I'm literally, right now, supporting two different queueing systems based on PG and Redis, so I get on a very real level, the tradeoffs. I know in great detail the problems that come up, but HN is not conducive to talking at that level of detail. At this point every comment I make is flagged and downvoted, so why would I pay time into a system that has clearly decided my opinion isn't relevant?
You're stuck in PG because your DevOps team is a bunch of incompetent dolts, so yeah, make the best out of the bad situation and go ahead and use something like Que.
Just don't develop Stockholm Syndrome while doing it.
People in this thread are protecting their own egos by expressing how great PG is as a message broker, but it's harmful to the industry to let that kind of attitude perpetuate.
Nothing is likely be correct about your arguments if you don't know what you are trying to fix or the sitation, which should also be blatantly obvious. You're applying some unstated subjective situation in your head, then dumping out something you've heard / done before. LOL.
Also "if you've ever used both" - I have, which is why I know. It's gray; sometimes you should, sometimes you shouldn't. You're assuming I haven't as I have differing point of view to you.
Like many things in this space there are a number of good ways - each with minor trade offs
Others posters have detailed those trades very clearly.
So now we can all be more educated about which one of the six good ways we'd choose.