In short, you can use blockchain as a distributed database, but it can also be used for something else. It's like a laptop. You can use it as a USB stick to store files and lug them around. But it can also be a computer, playing games and watching movies, no problem.
Distributed databases, as the name suggests, are distributed databases deployed on different machines (also known as "nodes"). On the face of it, this definition is indeed consistent with the effect that can be achieved by the "whole node saves all blocks" model in blockchain. That's why I mentioned earlier: blockchain can be used for distributed data storage.
But while the functions are similar, there are some obvious differences between the blockchain used for data storage and the actual distributed database.
1. They were designed to be completely different
Distributed database is the practice of distributed computing in database, in order to reduce costs and improve efficiency at the same time, so each node is mutual trust. Blockchain, on the other hand, is designed entirely to solve the problem of mistrust. This design makes blockchain far less efficient than a regular distributed database.
2. The amount of data stored by each node may be different
Data on a full node in a blockchain must be a full backup of all data, whereas nodes in a distributed database may not be. A typical example is HDFS in Hadoop. Each node stores only a part of the total data. In this way, the efficiency of each distributed node can be fully and effectively brought into play, and the parallel efficiency of subsequent queries can be improved.
3. The number of maintenance-data subjects may differ
Each node in a blockchain is owned by a different entity unless it is an individual who has built it himself, so a blockchain is a set of data records maintained by multiple entities. But the actual use of distributed database, in most cases only one subject, for security or efficiency reasons, the data distributed storage.
And group think, at this function as data storage, block chain there are some similarities and distributed database, also can achieve some of the basic features of the distributed database, but the underlying logic is completely different, more don't need to talk about both in the distributed system at the core of the large gap in CAP rules.
Although the blockchain as a distributed database has its natural shortcomings, but in the function of data processing, blockchain has its unique advantages.