Chapter 4. The Grouping API
The Grouping API can relocate groups of entries to a specified node or to a node selected using the hash of the group.
4.1. Grouping API Operations
Normally, Red Hat JBoss Data Grid uses the hash of a specific key to determine an entry's destination node. However, when the Grouping API is used, a hash of the group associated with the key is used instead of the hash of the key to determine the destination node.
Each node can use an algorithm to determine the owner of each key. This removes the need to pass metadata (and metadata updates) about the location of entries between nodes. This approach is beneficial because:
- Every node can determine which node owns a particular key without expensive metadata updates across nodes.
- Redundancy is improved because ownership information does not need to be replicated if a node fails.
When using the Grouping API, each node must be able to calculate the owner of an entry. As a result, the group cannot be specified manually and must be either:
- Intrinsic to the entry, which means it was generated by the key class.
- Extrinsic to the entry, which means it was generated by an external function.
