$model->getOrigData() returns the data that was originally loaded from the database when you initialized the model object and called $model->load() method. After loading the model you may have performed certain updates to the $model object calling methods like $model->setData(). $model->getData() return the $model object data in the present state.
Magento models extend the class ‘Mage_Core_Model_Abstract’ which in turn extends the class ‘Varien_Object’. The methods getData() and getOrigData() have been defined in the class ‘Varien_Object’.
Magento maintains several log tables for tracking purpose like customer access, products viewed, products compared etc. These tables grow in size day by day so if you have a large numbers of visitors on your website the size of these log tables may become large enough within a week slowing down your database. So you should perform database log cleaning on a regular basis – daily/weekly/monthly depending upon your website traffic.
There are three ways to clean out these tables:
1. Log Cleaning in the Magento Admin
2. Shell Utility log.php in the ../shell directory, and
3. Manually via phpMyAdmin or mysql client