Node repair topics.
Over time, data in a replica can become inconsistent with other replicas due to the distributed nature of the database. Node repair makes data on a replica consistent with data on other nodes and is important for every Cassandra cluster. Repair is the process of correcting the inconsistencies so that eventually, all nodes have the same and most up-to-date data.
- Hinted Handoff
During the write path, if a node that should receive data is unavailable, hints are written to the coordinator. When the node comes back online, the coordinator can hand off the hints so that the node can catch up and write the data.
- Read Repair
During the read path, a query acquires data from several nodes. The acquired data from each node is checked against each other node. If a node has outdated data, the most recent data is written back to the node.
- Anti-Entropy Repair
For maintenance purposes or recovery, manually run anti-entropy repair to rectify inconsistencies on any nodes.
Cassandra settings or Cassandra tools can be used to configure each type of repair. Depending on other conditions of the cluster, when to use each type of repair and how to configure them varies.