Tutorial

Google uses an amazing set of technologies. I use this article to keep information about this technology and to keep pointers to publicly available information about these technologies.

Pagerank is the weight of importance for a webpage calculated by Google.

The calculation process is not known and contains many factors but the principle is simple. A web page is more important if other web pages link to it. The more importance a web pages has (by inbound links from other sites) the more important are outbound links from this webpage.

Please find a good description of the pagerank calculation in the following article http://www.ams.org/featurecolumn/archive/pagerank.html .

Please see MapReduce .

Google has the GFS, a distributed, multi-gigabyte files. This file system is described Google File System Whitepaper .

GFS does not handle the replication between different data centers.

Please see Bigtable .

Google provides on the Google App Engine memcache as a caching mechanism.

Memcache is a high-performance, distributed memory object caching system, primarily intended for fast access to cached results of datastore queries.

Similar to Bigtable it works similar to a map with key and objects. If the memory consumption of memcache is to big then memory will automatically released based on a Last-Recently-Used (LRU) strategy.

Google provides an API to put something into memcache and to remove something again from memcache.

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