Ironically, Google does not make use of a relational database, but uses a multidimensional database called BigTable, which is built on the Google File System (GFS). Google's search algorithm is so complicated (or advanced), that it needs a specialized type of multidimensional database to support its specific needs.

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Reply from Richard Rost:

I did not know that. Thanks for the tip! I'll have to read up on it some more. Web search has always fascinated me.