Cluster State Management

Cluster state management is crucial in maintaining and coordinating operations within a CrateDB cluster. It's an essential mechanism that ensures efficient functioning of the database system.

Each node in the database cluster maintains a versioned copy of the latest cluster state. However, only one node within the cluster, known as the master node, has the ability to change the state at runtime. At any given moment, the cluster can have only one master node. The cluster becomes available to serve requests once a master has been elected. This election, which requires a majority among master-eligible nodes, is a crucial step in the process. When the master node updates the cluster state, it publishes the new state to all nodes within the cluster and waits for responses from each before it processes the next update. This ensures consistency and avoids potential conflicts within the cluster.

The cluster state encompasses all important information required for maintaining the cluster and coordinating its operations. This includes:

• Global cluster settings
• Discovered nodes and their status
• Schemas of tables
• The status and location of primary and replica shards