Data type and amount in human society is growing in amazing speed which is caused by emerging new services such as cloud computing, internet of things and social network, the era of big data has come. Data has been fundamental resource from simple dealing object, and how to manage and utilize big data better has attracted much attention. Evolution or revolution on database research for big data is a problem. This paper discusses the concept of big data, and surveys its state of the art. The framework of big data is described and key techniques are studied. Finally some new challenges in the future are summarized.