Big log file importing

I’m a big log file which will import data to piwik several days
Now I need to write a cron to import new data every few hours
How can I get piwik to analyze only the new value and not the all log file ?

use --skip= to skip to a given line

Alternatively I’m using two log files and purging temp one regularly (I’m running this hourly)

cp /var/log/apache2/temp.lgg /var/log/apache2/temp_import
: > /var/log/apache2/temp.lgg
python /piwik/misc/log-analytics/ --url=https://piwik /var/log/apache2/temp_import --idsite=3 >> log.txt
rm /var/log/apache2/temp_import
php5 /piwik/misc/cron/archive.php --url=http://piwik >> log.txt