Most webmaster split their logfiles each day or each month. The package is able to read such files. You'll need to specify the structure of your log filename.

Field Description Value (ex)
%prefixlog This is the filename core, i.e the constant string of your log filename. access
%day Day in the 01-31 range 02
%smallday Day in the 1-31 range 2
%month Month in the 01-12 range 03
%smallmonth Month in the 1-12 range 3
%lettermonth Month in the Jan-Dec range (first letter uppercase) Nov
%year Year in an 4 digits number 2000
%hour Hour in an 2 digits number 00
%min Minute in an 2 digits number 00
%sec Second in an 2 digits number 00
%smallyear Year in an 2 digits number 00
%rotate Number 1