Google Dance

GOOGLE DANCE



The name "Google Dance" has often been used to describe the index update of the Google search engine. Google's index update occurred on average once per month.

The Google search engine pulls its results from more than 10,000 servers. Naturally, an index update cannot be proceeded on all those servers at the same time. One server after the other has to be updated with the new index.

Not only Google's index is spread over more than 10,000 servers, but also these servers are, as of now, placed in 13 different data centers. These data centers are mainly located in the US (i.e. Santa Clara, California and Herndon, Virginia) and in Dublin, Ireland.

In order to direct traffic to all these data centers, Google could thoeretically record all queries centrally and then send them to the data centers. But this would obviously be inefficient. In fact, each data center has its own IP address (numerical address on the internet) and the way these IP addresses are accessed is managed by the Domain Name System.(DNS)

During the Google Dance, the data centers do not receive the new index at the same time. In fact, the new index is transferred to one data center after the other. When a user queries Google during the Google Dance, he may get the results from a data center which still has the old index at one point im time and from a data center which has the new index a few minutes later. From the users perspective, the index update took place within some minutes. But of course, this procedure may reverse, so that Google switches seemingly between the old and the new index.

IP Addresses and Domains of Google's Data Centers:

The progression of a Google Dance could basically be watched by querying the IP addresses of Google's data centers. But queries on the IP addresses are normally redirected to www.google.com. However, Google has domains which resolve to the single data centers' IP addresses. These domains as well as their IP addresses are shown in the following list.

Domain	IP-Adress
www-ex.google.com	216.239.33.100
www-sj.google.com	216.239.35.100
www-va.google.com	216.239.37.100
www-dc.google.com	216.239.39.100
www-ab.google.com	216.239.51.100
www-in.google.com	216.239.53.100
www-zu.google.com	216.239.55.100
www-cw.google.com	216.239.57.100
www-fi.google.com	216.239.41.100
www-gv.google.com	216.239.59.100
www-kr.google.com	66.102.11.100
www-mc.google.com	66.102.7.100
www-lm.google.com	66.102.9.100