Hash Functions

Good Hash Functions:

• If key distribution P is known, then the hash function should satisfy
  
  $$\sum_{k: \;h(k) \;=\; j} P(k) \;=\; \frac{1}{m} \;\;\;{\rm for} \;j=0,..,m-1$$
  
  

• Heuristics
  • Design hash function such that similar keys map to different slots (e.g. name1, name2)
  • Hash value should be independent of data patterns