Why do the retention policy not work accurately


Here is the retention policy on “temp” database. The odd thing is that I set the retention policy 1 hour but 2-hour data is kept. What’s wrong with my retention policy? BTW, what’s exact function of replication? I read the document but I do not know its function.
Excuse my poor expression.


Here is the visualization of “temp” database. It’s easy to see that 2-hour data has been kept


BTW!!! Why the old data will disapear when I change the retention policy?