Using RSS in WordPress can have a lot of benefits, however, there is also one major drawback. It will cause severe bloating of the WordPress Options table, and if the WordPress Options table is too large it will slow a blog down to a crawl.
To solve this problem you can clean out the RSS Hash entries using a plugin such as Clean Options. This plugin will also help you find and remove all those Orphaned records created by plugins that do not remove their own entries.
To stop Magpie from creating these entries in the future you can disable Magpie Cache by inserting the following into your WordPress Theme function file.