1 Bloom filter

 When we write crawler,  if we have to crawler millions websites,  we need to check whether a website is crawled or not,

 So we need both space and time efficient algorithoms to achieve this goal, is our choice.

 Bloom filter is a probabilistic data structure: it tells us that the element either definitely is not in the set or may be in the set.

 So  Bloom filter may be false positive, but never false negative.

 About false positive and false negative, you can refer to  and ".

 

2 Use case

  a) search engine, when crawls website, check whether a website is crawled or not.

  b) browses use this to check whether a url is malicious or not.