Iterator for iterating map entries in the partitionId. The values are not fetched one-by-one but rather in batches.
The Iterator.remove() method is not supported and will throw an UnsupportedOperationException.
Iterating the map should be done only when the IMap is not being
mutated and the cluster is stable (there are no migrations or membership changes).
In other cases, the iterator may not return some entries or may return an entry twice.