How are variations stored?

Can anyone tell me the basic database structure of where/how the variations are stored?

I'm currently using another (non WPMUdev) plugin for a shopping cart and it's storing the variations in the wp_postmeta table... and when I have a product with multiple variation "sets" (each with many variation options), the database literally just blows thru the roof because so many rows are created in the table. I am trying to find out if your plugin does the same, or how it handles multiple (as in, TONS and TONS) of variations and options...