Over time, Magento installs can become bloated with unnecessary data, the main culprit here is the log tables such as log_url in the database. They can get very large and eventually slow down your Magento install. The log tables that can be safely truncated include:
The easiest way to clean these tables is via SSH, log into your server and navigate to the webroot then run the following command:
php shell
/log
.php clean
