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Google_Cluster_Architecture.md

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Google的分布式搜索架构

WEB SEARCH FOR A PLANET :THE GOOGLE CLUSTER ARCHITECTURE

Serving a Google query

  1. 用户查询 www.google.com/search?q=ieee+society
  2. DNS lookup to map www.google.com to a particular IP address, 谷歌在全球有多个集群, 这一步会利用 DNS-based load-balancing system selects a cluster by accounting for the user’s geographic proximity to each physical cluster.
  3. The user’s browser then sends a hypertext transport protocol (HTTP) request to one of these clusters. 然后该集群内也有自己的负载均衡策略，会选择该集群内的一台机器处理该请求，处理完后再返回给用户.

Index Server : 比如我要查询 梅西&美国. 利用inverted index, 我知道梅西对用Document1,2,4，美国对应Document2,5,7.那么我取一次交集，知道最终要取得Document2.

Document Server : Document servers fetching each document from disk to extract the title and the keyword-in-context snippet. The docserver cluster must have access to an online, low-latency copy of the entire Web. In fact, because of the replication required for performance and availability, Google stores dozens of copies of the Web across its clusters.

Spell checker & Ad server : In addition to the indexing and document-serving phases, a GWS also initiates several other ancillary tasks upon receiving a query, such as sending the query to a spell-checking system and to an ad-serving system to generate relevant advertisements (if any).

When all phases are complete, a GWS generates the appropriate HTML for the output page and returns it to the user’s browser.