Google dance refers to the monthly update of the Google search engine database. This can lead to different search engine responses for simultaneous, identical searches. This phenomenon was mainly observed up to 2003. Currently, the rankings are updated almost hourly.
Google now gets its search results from over 10,000 networked Linux computers which are in turn joined to computing units (called clusters). Compared to the early years of Larry Page and Sergey Brin with 2-3 Linux servers, it now requires organization and sufficient space for the large number of computing units. The computers are therefore placed in different data centers, each of which have their own index and are mutually closely linked. The space required covers several football fields in order to accommodate all servers. This division of computing centers ensures high reliability for the Google search engine. Moreover, new features can be tested independently, without reference to or influence on the official index.
Earlier, the update of the database was carried out at intervals of about one month. First the individual data centers were separately processed and were then completed by updating the index. Since the positions in the search results could often change during the adjustment phase, it was called the Google dance. Experts then developed specialized tools which queried each datacenter simultaneously. The results could be displayed side by side and compared, making trend estimates possible.
Even outside the Google dance phase, changes in rankings were possible especially with websites that frequently change their content. Occasionally even daily updates could be observed. However, this was of considerably lesser extent compared with Google Dance.
Google dance nowadays is hardly an issue any more. The Google algorithm has been developed to such an extent that an update of the indices happens multiple times a day. This makes it difficult for SEO specialists and website operators to make accurate estimates and calculations on website ranking.