The db.log files are not dated, the entries could have been from a long time ago, such as the fork caused by pre-0.8 clients choking on a big block. Delete.
The log file is for Berkeley databases, which is only the wallet and peers database files now. Humongous wallet?
You can add a config option to increase some of the database parameters (
https://bitcointalk.org/index.php?topic=152208.msg1615346#msg1615346), but it is better for all for you to clear the logs and see if this ever occurs again, and if devs can reproduce or fix it with information about your client or files.
