Set the Number of Redundant Copies

Configure in-memory high availability for your partitioned table by specifying the number of secondary copies you want to maintain REDUNDANCY clause of CREATE TABLE.

Because GemFire XD is primarily a memory-based data management system, it is important to use redundancy when necessary to enable fail-over if a member shuts down or fails. However, keep in mind that maintaining a large number of redundant copies has an adverse impact on performance, network usage, and memory usage. A REDUNDANCY value of 1 is recommended to maintain a secondary copy of the table data. For example:
CREATE TABLE COUNTRIES
(
  COUNTRY VARCHAR(26) NOT NULL,
  COUNTRY_ISO_CODE CHAR(2) NOT PRIMARY KEY,
  REGION VARCHAR(26),
)
REDUNDANCY 1

GemFire XD attempts to place copies of the same bucket onto hosts that have different IP addresses if possible, to protect against machine failure. However, if there is only one machine available GemFire XD places multiple copies on that machine. Setting the enforce-unique-host boot property prevents GemFire XD from ever placing multiple copies on the same machine.

Set the redundancy-zone boot property to ensure that GemFire XD places redundant copies on specific zones that you define. For example, to ensure that redundant copies are placed on different racks, set the redundancy-zone for each machine to the logical name of the rack on which the machine runs.

If the primary and secondary buckets for a partition are unavailable, then queries to the table can fail. For a persistent table, queries involving missing buckets fail with a PartitionOfflineException. Queries across the entire table would also fail. Queries to non-persistent tables with missing partitions can return empty results.