"The Webmap build starts with every Web page crawled by Yahoo! and produces a database of all known Web pages and sites on the internet and a vast array of data about every page and site. This derived data feeds the Machine Learned Ranking algorithms at the heart of Yahoo! Search. Some Webmap size data:
- Number of links between pages in the index: roughly 1 trillion links
- Size of output: over 300 TB, compressed!
- Number of cores used to run a single Map-Reduce job: over 10,000
- Raw disk used in the production cluster: over 5 Petabytes"
Doug Cutting used to work at PARC, and we have been using Hadoop heavily in our research as well.