Replicated Map

A replicated map is a weakly consistent, distributed key-value data structure provided by Hazelcast.

All other data structures are partitioned in design. A replicated map does not partition data (it does not spread data to different cluster members); instead, it replicates the data to all nodes.

This leads to higher memory consumption. However, a replicated map has faster read and write access since the data are available on all nodes and writes take place on local nodes, eventually being replicated to all other nodes.

Weak consistency compared to eventually consistency means that replication is done on a best efforts basis. Lost or missing updates are neither tracked nor resent. This kind of data structure is suitable for immutable objects, catalogue data, or idempotent calculable data (like HTML pages).

Replicated map nearly fully implements the java.util.Map interface, but it lacks the methods from java.util.concurrent.ConcurrentMap since there are no atomic guarantees to writes or reads.

import com.hazelcast.core.Hazelcast;
import com.hazelcast.core.HazelcastInstance;
import java.util.Collection;
import java.util.Map;

HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();
Map<String, Customer> customers = hazelcastInstance.getReplicatedMap("customers");
customers.put( "1", new Customer( "Joe", "Smith" ) );
customers.put( "2", new Customer( "Ali", "Selam" ) );
customers.put( "3", new Customer( "Avi", "Noyan" ) );

Collection<Customer> colCustomers = customers.values();
for ( Customer customer : colCustomers ) {
  // process customer

HazelcastInstance::getReplicatedMap returns com.hazelcast.core.ReplicatedMap which, as stated above, extends the java.util.Map interface.

The com.hazelcast.core.ReplicatedMap interface has some additional methods for registering entry listeners or retrieving values in an expected order.

image NOTE: Replicated Map is in the beta stage.