One of the distributed data structures supported by Hazelcast is MultiMap.
It is very useful container as it stores a collection of values mapped to given key.
But as you know you can always use an Map as MultiMap.
Just create a set or list for each new key, and add to this collection in each put operation.
But in Hazelcast’s distributed world, MultiMap has extra benefits.
Hazelcast optimized the MultiMap operations so that operations (put, remove, containsValue and containsEntry) do not serialize, deserialize the whole collection.
Instead just the added or retrieved object is processed.
Note: This information is extracted from a conversation in Hazelcast mail group.
For more you can join the group.