1.why do we consist hashing？
problem:
if we just use the normal hashing, for example, firstly we have 3 nodes in our db system,
all the hashcode%3==0 go to node1
all the hashcode%3==1 go to node1
all the hashcode%3==2 go to node2
but if we add one more node3, all the data in node0~2 need to be rehashing.
2.what is consist hashing?
Consist hashing is a kind of hashing that when hash table is resized , only keys/slots of keys need to be remapped on average.
We can consider consist hashing as a hash ring, the ring has been divided 360(in the real condition it's 232).
When we add a node , we would randomly select K point from the ring.
what is virtual nodes? <明天補充>
3.what is the advantage of consist hashing?
when we add/remove a new node, least of data will be affected.
because we use the virtual nodes mechnism (one real node will process several virtual nodes data), so when we remove a node, it would not give the impact to a single node(since there'are several virtual nodes).
data can be more balanced assigned to nodes
4.how to implement the consist hashing?
the related algrithm to understand the consist hashing:
https://www.lintcode.com/problem/520/