GemFire XD server
groups control which GemFire XD data store members replicate the table's data.
GemFire XD replicates table data both when a new table is initialized in a cluster
and when replicated tables are updated.
How GemFire XD Replicates Tables
GemFire XD replicates every single row of a replicated table synchronously to each table replica in the target server group(s). With synchronous replication, table reads can be evenly balanced to any replica in the cluster, with no single member becoming a contention point.