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Google Dance Tool
在升级期间，新的网页被加入，无效网页被删除，对收录网站进行全面深度检索，也可能在这期间调整算法。Goolge搜索结果显示出剧烈的排名波动，同时被索引网站的外部链接也获得更新。每个季度更新一次的网页级别（Page Rank）也发生在Google dance期间。Dance一般持续几天时间，Dance结束后，Google搜索结果和网站外部链接数量趋于稳定，直至下一个周期的Google dance到来。
Google Dance 是Google定期更新它的索引的活动，给人感觉就像是跳舞一样。在这个Dance的过程中，Google所储存的索引都被重新更新，网站的排名会发生剧烈变化，有的网站在Google上的排名一夜之间消失，有的网站则名列首位。Google Dance通常在月末的那周开始，新结果在月初几天可以看到，大概是每36天一次或者一年10次。
Google dance 是Google完善自己的算法、反对垃圾泛滥的努力。Google dance出现之后，使许多SEO从业者开始反思如何正确地使用技术来优化网站。只要你的网站没有作弊或者使用什么不好的技术，那就不怕Google Dance，所以，即使有一天你突然发现你的网站排名突然后退很多或者在Google上找不到了，也不要太担心，因为可能是Google在翩翩起舞。
Google Dance Tool 顾名思义，是检测Google dance期间的关键词的google搜索排名情况。
Checks Google servers to determine if there is an update in progress.
The google dance tool is designed to help webmasters determing when the google dance has started and google is spidering the internet.
The Google Dance Tool is provided as a tool to help you, the webmaster, determine when the Google search engine is spidering the internet. This is extremely useful if you want to know when your site(s) will rank in Google.
The name Google Dance is a term used to describe the index update of the Google search engine. By using the Google Dance Tool below, you can easily determine if Google has started their monthly spidering of the internet. Type in a keyword you would like to search for and choose some of Google's data centers to perform the search query on. You will then see a page displaying the search results of all the Google data centers you have chosen. If any of the results between the different data centers contain discrepencies, then you know that Google has started to spider.
We have also written a nice little script that is FREE for you to use that has deamed itself useful. With the use of the Google Web API, it is now possible to perform search queries on the Google search engine to find information concerning a variety of information. These include how many sites link to yours site, search results on any particular keyword, your site's ranking in Google, and much more.
What Is A Google Dance?
The name "Google Dance" is often used to describe the index update of the Google search engine. Google's index update occurs on average once per month. It can be identified by significant movement in search results and especially by Google's cache of all indexed pages reflecting the status of Google's last spidering. But the update does not proceed as a switch fro m one index to another at one point in time. In fact, it takes several days to complete the index update. During this period, the old and the new index alternate on www.google.com. At an early stage, the results fro m the new index occur sporadically. But later on, they appear more frequently. Google dances.
Technical Background on Google
The Google search engine pulls its results fro m more than 10,000 servers which are simple Linux PCs that are used by Google for reasons of cost. 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.
Many webmasters think that, during the Google Dance, Google is in some way able to control if a server with the new index or a server with an old index responds to a search query. But, since Google's index is inverse, this would be very complicated. As we will show below, there is no such control within the system. In fact, the reason for the Google Dance is Google's way of using the Domain Name System (DNS).
Google Dance and DNS
Not only Google's index is spread over more than 10,000 servers, but also these servers are, as of now, placed in eight different data centers. These data centers are mainly located in the US (i.e. Santa Clara, California and Herndon, Virginia), indeed, in June 2002 Google's first European data center in Zurich, Switzerland went online. Very likely, there are more data centers to come, which will perhaps be spread over the whole world. However, in January and April 2003 Google has put two data centers on stream which are again located in the US.
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.
Basically, the DNS works like this: On the Internet, data transfers always take place in-between IP addresses. The information about which domain resolves to which IP address is provided by the name servers of the DNS. When a user enters a domain into his browser, a locally configured name server gets him the IP address for that domain by contacting the name server which is responsible for that domain. (The DNS is structured hierarchically. Illustrating the whole process would go beyond the scope of this paper.) The IP address is then cached by the name server, so that it is not necessary to contact the responsible name server each time a connection is built up to a domain.
The records for a domain at the responsible name server constitute for how long the record may be cached by a caching name server. This is the Time To Live (TTL) of a domain. As soon as the TTL expires, the caching name server has to fetch the record for a domain again fro m the responsible name server. Quite often, the TTL is set to one or more days. In contrast, the Time To Live of the domain www.google.com is only five minutes. So, a name server may only cache Google's IP address for five minutes and has then to look up the IP address again.
Each time, Google's name server is contacted, it sends back the IP address of only one data center. In this way, Google queries are always directed to different data centers by changing DNS records. On the one hand, the DNS records may be based on the load of the single data centers. In this way, Google would conduct a simple form of load balancing by its use of the DNS. On the other hand, the geographical location of a caching name server may influence how often it receives the single data centers' IP addresses. So, the distance for data transmissions can be reduced. In order to show the DNS records of the domain www.google.com, we present them here by the example of one caching name server.
How data centers, DNS and Google Dance are related, is easily answered. 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 fro m a data center which still has the old index at one point im time and fro m 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.
The Google Dance Test Domains www2 & www3
The beginning of a Google Dance can always be watched at the test domains www2.google.com and www3.google.com. Those domains normally have stable DNS records which make the domains resolve to only one (often the same) IP address. Before the Google Dance begins, at least one of the test domains is assigned the IP address of the data center that receives the new index first.
Building up a completely new index once per month can cause quite some trouble. After all, Google has to spider some billion documents an then to process many TeraBytes of data. Therefore, testing the new index is inevitable. Of course, the folks at Google don't need the test domains themselves. Most certainly, they have many options to check a new index internally, but they do not have a lot of time to conduct the tests.
So, the reason for having www2 and www3 is rather to show the new index to webmasters which are interested in their upcoming rankings. Many of these webmasters discuss the new index at the Google forums out on the web. These discussions can be observed by Google employees. At that time, the general public cannot see the new index yet, because the DNS records for www.google.com normally do not point to the IP address of the data center that is updated first when the update begins.
As soon as Google's test community of forums members does not find any severe malfunctions caused by the new index, Google's DNS records are ready to make www.google.com resolve the the data center that is updated first. This is the time when the Google Dance begins. But if severe malfunctions become obvious during this test phase, there is still the possibility to cancel the update at the other data centers. The domain www.google.com would not resolve to the data center which has the flawed index and the general public could not take any notice about it. In this case, the index could be rebuilt or the web could be spidered again.
So, the search results which are to be seen on www2.google.com and www3.google.com will always appear on www.google.com later on, as long as there is a regular index update. However, there may be minor fluctuations. On the one hand, the index at one data center never absolutely equals the index at another data center. We can easily check this by watching the number of results for the same query at the data center domains listed above, which often differ fro m each other. On the other hand, it is often assumed that the iterative PageRank calculation is not finished yet, when the Google Dance begins so that preliminary values exert influence on rankings at that point in time.
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