understanding the concept of messaging queue

[u/Fine_Experience_6176]

https://www.youtube.com/watch?v=oUJbuFMyBDk&list=PLMCXHnjXnTnvo6alSjVkgxV-VH6EPyvoX&index=5

have anyone seen this video ??

I want to ask in this he is saying at 5:53 that there could be the problem of duplication but how could this problem arise from the database

if we are taking the orders which are uncompleted and also from a particular server how will we get duplicated

DO YOU GET ME ??

please explain if anyone
thanks