Why do we need message brokers like RabbitMQ over a database like PostgreSQL?

I am new to message brokers like RabbitMQ which we can use to create tasks / message queues for a scheduling system like Celery.

Now, here is the question:

• I can create a table in PostgreSQL which can be appended with new tasks and consumed by the consumer program like Celery.

• Why on earth would I want to setup a whole new tech for this like RabbitMQ?

Now, I believe scaling cannot be the answer since our database like PostgreSQL can work in a distributed environment.

I googled for what problems does the database poses for the particular problem, and I found:

• polling keeps the database busy and low performing
• locking of the table -> again low performing
• millions of rows of tasks -> again, polling is low performing

Now, how does RabbitMQ or any other message broker like that solves these problems?

Also, I found out that AMQP protocol is what it follows. What’s great in that?

Can Redis also be used as a message broker? I find it more analogous to Memcached than RabbitMQ.

Please shed some light on this!