Magento database log cleaning
Log tables:
log_customer
log_visitor
log_visitor_info
log_url
log_url_info
log_quote
report_viewed_product_index
report_compared_product_index
report_event
catalog_compare_item
Cleaned by script:
php -f shell/log.php clean
Cleaned by Magento Admin (By default, it is disabled.):
From the Magento Admin Panel, select System > Configuration
On the left, locate the Advanced menu and click System
From the System panel, click Log, and from the Enable Log Cleaning drop-down list, select Yes
In the Save Log Days field, enter 15 (The value is based on how much the traffics are)
Click Save Config
Clean those tables manually with Mysql client or phpMyAdmin (NOT recommend)
Source: https://docs.nexcess.net/article/how-to-perform-magento-database-maintenance.html
Written on March 30, 2017