[kerblang]

Overall it's completely feasible to build a message queue with RDBMS _because_ they have locking. You might end up doing extra work compared to some other products that make message queueing easy/fun/so-simple-caveman-etc.

Now if SQS has some super-scalar mega-cluster capability where one instance can deliver 100 billion messages a day across the same group of consumers, ok, I'm impressed, because most MQ's can't, because... locking. Thus Kafka (which is not a message queue).

I think the RDBMS MQ should be treated as the "No worse than this" standard - if my fancy new message queueing product is even harder to set up, it isn't worth your trouble. But SQS itself IS pretty easy to use.