nothing, go away

# PostgreSQL 9.4.5
result 38~40 second


# MySQL 5.7.10
result 38~40 second


# SSDB 1.9.2
result 19~20 second

# cassandra 3.0.2
result 27 second



# SQL database 

Pros.
======

    Rich query and relational stucture.

    everyone know it.

Cons.
=====

    Support Master (Master or Slave), need to shard db to scale write.

# SSDB

Pros.
======
    Fastest 

Cons.
=====
    query language support key query. 
    same with sql db, need to scale write.

# Cassandra

Pros.
======
    Easy setup event on cluster
    scale read && write
    support TTLi(time to live), good to log event.

Cons.
=====
    Query language have to adapt the data model
    Query lanuage without OR, NOT.