The chain structure of the existing blockchain leads to TPS and concurrency cannot be improved. based on this, many new blockchain projects and papers are published, and the DAG is one of the most colorful ones.
In graph theory, if a directed graph from any vertex can not go through several edges back to the point, this graph is a Directed Acyclic Graph.
In 2015, a heterogeneous blockchain project was born under the research of mathematician Serguei Popov and geek Dominik Schiener, among others, iota.At the beginning of the emergence, it caused great controversy, with the traditional structure of the block chain is completely different, they will transform the block chain into a block diagram.The DAG is applied to the blockchain to solve the problem of concurrency and low TPS.
Since then, the DAG has emerged as an emerging technology representative with a number of DAG-based projects. Byteball-based on Dag and witness mechanism, rchain-combines DAG with Casper.There is also the famous DAGlabs organization, founded in Israel’s Hebrew University, they published spectre and phantom two DAG-based blockchain papers.
In 2016, an academic paper was published, marking another possible emergence of DAG in the blockchain world-Hashgraph.Hashgraph successfully integrated Dag and Byzantine Fault Tolerance systems together to solve the DAG in the byzantine system reliability proof, proposed deterministic probability can reach the traditional block chain will never reach 1.But because of copyright restrictions and Dag width Hashgraph problem, resulting in very little use in the actual project, therefore, there has been a number of projects on this basis, in order to solve the problem of Dag width.
Early Block Chain project, based on the chain structure as the basic data format, has maintained a single chain structure extended down, the characteristics of the data structure is simple and efficient, clear and easy to understand. The downside is that parallelism is severely limited and there is no way to achieve high throughput. Single-chain structure also led to a lot of bifurcation, bifurcation means a serious waste of resources.
Dag project using its scalable and scalable graph structure, you can smoothly expand its width, the greater the number of transactions, Dag graph structure can also be fully processed, throughput capacity is high, the speed is limited only by external factors such as the network. The disadvantage is that the width can not be limited, easy to cause collapse Dag width, most nodes can not synchronize information, resulting in a graph to the direction of the vertex extends down.
DAG in solving performance bottlenecks, but also introduced such as Dag width, the number of nodes is limited and other issues, a simple DAG has been difficult to carry the actual needs, DAG and other technology combined approach began to go on the stage of history.