woothemes/woocommerce — pull request #3591 by Gator92 (2013-08-06 04:34:54+00:00)
Title: Adds an index to the foreign key in table woocommerce_tax_rate_locations

The index is missing for the foreign key on the table woocommerce_tax_rate_locations. When there are a number of entries in this table, such as there would be for a state like California, the tax rate class queries grind to a halt becoming a significant bottleneck for the application.