need explain about atop logging system

Question

I'm not a infra/system engineer, but I need to monitor device resource history.

I heard 'atop' is a good tool to monitor resource device, so I install in it.

Document says that atop automatically generate log in '/var/log/atop/atop_XXXXXX/'.

I found that logs there, but some day was not recorded...

Is there anyone to explain about how does atop logging system execute? and how to manipulate it?

Thanks in advance.