A message queue is like a database except people can open a socket and say "notify me when there is a new value for this key" -- and you can chose to let multip

A message queue is like a database except people can open a socket and say "notify me when there is a new value for this key" -- and you can chose to let multiple people get in line for such updates and then wether you want to let everyone know or just the first person or so-on. you can implement all of this on any db with polling and locks, but that is not an efficient way to do things.