APM logs (BIGIP 13.0.0)

Here are another article relating the use of mysql to store session reports. Some commands looks like really interesting for you : K17089: The BIG-IP APM MySQL database may grow to consume all available disk space

APM log file and session reports are not directly linked.

Here an abstract of another article I found :

To control database log rotation and maximum log entries
1.
From the Main tab, select Access Policy > Reports > Preferences.
The Preferences window opens.
2.
In the Log Rotation Period box, type a number between 0 and 90. The default value is 0. 
When set to 0, log database tables are rotated only when the database contains the maximum number of log entries.
When set to a value between 1 and 90, log database tables are rotated every n number of days. (If the maximum number of log entries is reached despite regular rotation, log database tables are rotated regardless.)
3.
In the Maximum Number Of Log Entries box, type a number between 100000 and 5000000 (100,000 and 5,000,000). Do not type commas. The default value is 5000000.

So, you have the preference menu in the GUI that allow you to control the session report logging settings.