I'm moving log files. The program has an inode open, not the file name, so it continues to write to the old files.
Any apache processes currently serving users continue with the current request and die.
Processes that are waiting for a request die instantly, and all are replaced with new processes. I do it at midnight each day, when traffic is low, but my understanding of a graceful restart is that there is no downtime at all. This also works for syslog files. It also blindly keeps writing the old files till the restart signal is sent.