Google Dance - The Index Update of Google

"Google Dance" refers to the index update of the Google search engine.

Technical Background

Google is used by many people and so, it retrieves its results from more than 10.000 servers. Not only Google's index is spread over more than 10.000 servers, but also these servers are 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.

Depending on your location, you will pull results from a different server. This is called 'load balancing ', so that you can enjoy a fast transfer of data, and see results in a very short time. If everybody would use the same server at the same time, and sending many queries to this same machine, it would make Google unworkable. So, Google consist out of a network of servers.

Google's index update

Google continiously gathers data about websites, it builds an index with this data and centralizes this index on a server. More or less every month, the datacenters are updated with the new index. During this 'index update' (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 in 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.

Conclusion

During the index update or Google Dance, it is possible that two users in different locations will see different results for the same query.

SERP Scanner and Google Dance

As the interface you are using to test your query (Test accuracy), is located on a server in the US, which gathers google SERP from its closest google-server. And while maybe you are located somewhere else (even within US), you might see different results on a manual search within google. This is when the index update takes place.