That's totally normal. If you choose filesystem as cache storage, you'll also notice rapid increasing of the number of files, and that's the same behavior you see in the database.
It's better if you use filesystem as cache storage, in order to decrease load on database.
I've found one comparison chart, you can check how it looks, and how to configure various type of cache storages:
http://magebase.com/magento-tutorials/magento-session-storage-which-to-choose-and-why/
It's better if you can use Redis / Memcached for cache storage.
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