How do DNS logs overwrite?

I am feeding DNS logs to a syslog server using LogParser with a check file and a scheduled task running every couple minutes.

When the log grows to the max size, 1gb, it overwrites by truncating some random amount of the log. 

How can I be sure I'm not missing logs?  

Can we configure it to FIFO, or retain some amount of the log file when it truncates to avoid missing logs?