CockroachDB is a Survivable, Thriveable and Scalable distributed SQL database. A winning formula for modern, mission critical applications at scale. To maintain its goal of being all three it uses the RAFT protocol to align and agree on one single state
So, what is RAFT?
The RAFT protocol is a consensus algorithm for distributed systems that is designed to be easy to understand and implement. It was introduced by Diego Ongaro and John Ousterhout in 2014 and has gained widespread adoption in the industry due to its simplicity and effectiveness.
The purpose of a consensus algorithm like RAFT is to ensure that all nodes in a distributed system agree on a single state, even in the presence of failures or network partitions. The basic idea of RAFT is to elect a leader among the nodes, who is responsible for making all decisions and ensuring that all nodes agree on the state. If the leader fails or becomes unreachable, a new leader is elected through a process of voting among the remaining nodes.
The RAFT protocol has three main components:
- Leader election: Nodes in the cluster communicate with each other to elect a leader. The leader is responsible for receiving client requests, replicating them to other nodes, and making decisions based on the replicated requests.
- Log replication: The leader maintains a log of all committed transactions and sends log entries to other nodes. When a node receives a new log entry, it applies the entry to its state machine to ensure that its state is consistent with the leader.
- Safety: RAFT ensures that all nodes agree on the same state by ensuring that a majority of nodes must agree on any decision before it is committed. This ensures that there is no possibility of two different leaders emerging and making conflicting decisions.
Overall, the RAFT protocol provides a reliable and efficient way to ensure consistency in distributed systems, making it a popular choice for building fault-tolerant and highly available systems.
How does CockroachDB use RAFT
CockroachDB is a distributed relational database that uses the RAFT protocol to ensure consistency and reliability across its nodes. CockroachDB uses the RAFT protocol to implement its distributed consensus algorithm, which is responsible for electing a leader node, replicating data to all nodes, and maintaining consistency across the cluster.
CockroachDB's use of RAFT involves the following steps:
- Leader election: The first step in the RAFT protocol is to elect a leader node. CockroachDB uses a modified version of the RAFT algorithm that ensures that a new leader is elected quickly if the current leader fails. This modified version of the algorithm is designed to minimize the impact of network partitions and ensure that the cluster remains available and responsive.
- Log replication: Once a leader has been elected, it begins replicating its log to all other nodes in the cluster. The log contains all committed transactions, and each node applies these transactions to its state machine to ensure that its state is consistent with the leader.
- Committing transactions: To ensure that all nodes agree on the same state, RAFT requires that a majority of nodes must agree on any decision before it is committed. CockroachDB uses the RAFT protocol to ensure that all committed transactions are replicated to a majority of nodes before they are considered complete.
- Fault tolerance: CockroachDB uses the RAFT protocol to ensure fault tolerance by replicating data to multiple nodes. This ensures that the system remains available even if some nodes fail or become unreachable.
In summary, CockroachDB uses the RAFT protocol to ensure that all nodes in the cluster agree on the same state and to provide fault tolerance and high availability in the face of failures and network partitions. By using the RAFT protocol, CockroachDB provides a reliable and efficient way to maintain consistency and reliability across a distributed system.