题目内容
There are two measures, namely freshness and age, indicating the local copy is accurate or outdated.
查看答案
搜索结果不匹配？点我反馈
更多问题
It's difficult for a server to satisfy multiple requests per second and/or downloading large files from a single crawler or the requests from multiple crawlers.
To use Web crawlers will cost a lot of network resources.
If the frequency of accesses to a given server is too high, it will suffer from severoverload.
As long as a crawler downloads pages, it is sure to be able to handle them.
微信支付 
支付宝支付