The logs are rotated by a nightly cron job using the script named
Its main configuration file is
You can get help on how to configure it using the command Pay attention to the "weekly", "daily", "monthly" keywords. There is also a "rotate" keyword that defines the number of rotations to keep. For example
keeps 4 weeks of logs, (1 active and 3 archives).
There is also a "compress" keyword that is used to gzip (or is it zip?) the archived logs.
Many packages have their individual logrotate configuration files. and these are located in this directory These files override the settings in the /etc/logrotate.conf file for each package specified in /etc/logrotate.d
Squid should have a file in there named "squid". The keywords mentioned above will apply.