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Replicated Map

A replicated map is a distributed key-value data structure where the data is replicated to all members in the cluster.

Replicating Instead of Partitioning

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 members.

This leads to higher memory consumption. However, a replicated map has faster read and write access since the data are available on all members.

Writes could take place on local/remote members in order to provide write-order, eventually being replicated to all other members.

Replicated map is suitable for 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.

image NOTE: If Replicated Map is used from a dummy client and this dummy client is connected to a lite member, the entry listeners cannot be registered/de-registered.

image NOTE: You cannot use Replicated Map from a lite member. A com.hazelcast.replicatedmap.ReplicatedMapCantBeCreatedOnLiteMemberException is thrown if com.hazelcast.core.HazelcastInstance#getReplicatedMap(name) is invoked on a lite member.

Example Replicated Map Code

Here is an example of replicated map code. The HazelcastInstance getReplicatedMap methods gets the replicated map, and the replicated map put creates map entries.

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.