redis - Using Hashes

Question

I\'m implementing a social stream and a notification system for my web application by using redis. I\'m new to redis and I have some doubts about hashes and their efficiency.

Answer 1

Basically, they want the number of values stored in a single hash to not exceed 1000. Probably, they set up their Redis instance configuration to work nicely with this number (thy set hash-zipmap-max-entries).

Every time an hash will exceed the number of elements or element size specified it will be converted into a real hash table, and the memory saving will be lost.

-- http://redis.io/topics/memory-optimization

As I understand, your question is "why exactly 1000 and not more?" Well, it's because they had to choose between space efficiency and speed. Space-efficient representation has operation complexity O(N), not O(1) as normal hashes - it is N times slower, but takes less memory.

They tested different values and found that 1000 is a good compromise solution - takes not much space, yet still fast enough.