计算机网络系列（7）之应用场景Search engine

1. Search engine
A search engine is a computer program for searching information on the web.

1.1. Steps
Step1: Gathering information
Step2: Serving requests

2. Ranking search
The keywords appear many times
The keywords appear in the title
Many other pages are linked to this page
This page is accessed by more users

3. Other types of search engines
Make use of multiple search engines to give more comprehensive search results.

4. Questions
Q1: We have learned how a search engine collects information and serves users. In practice, a search engine has to tackle many practical problems. Identify these possible problems and suggest how you would tackle them.

problem1: updated data
solution1: update pages of search engine servers

problem2: some pages are updated too frequently
solution2: identify them and update them frequently

problem3: too large database
solution3: decentralized + distributed database

problem4: disk fail
solution4: replication

5. 总结
重点1：搜索引擎的功能类型一个相对及时的网络proxy，为网络用户提供相对及时的网络信息。这里面涉及到及时性问题，存储问题，并发访问问题，单点错误问题，大问题。