Google’s document servers contain cached copies of virtually the entire World Wide Web on their hard drives. Each data center would have its own document server cluster, and each document server cluster would need to hold at least two copies of the Web, in order to provide redundancy in case of server failure. But document servers are not merely data warehouses. They also perform retrieval of the page title and keyword-in-context snippet from the document ID provided by the index servers. As the search is running, the peripheral systems also add their content to the page as the search is in progress. This includes the spell check and the advertisements. … Continue reading Fiach Reid