Package com.hazelcast.spi.merge

Interface SplitBrainMergePolicy<V,T extends MergingValue<V>,R>

Type Parameters:
V - the (deserialized) type of the merging value
T - the type of the required merging value, e.g. a simple MergingValue<V> or a composition like MergingEntry<String, V> & MergingHits & MergingLastAccessTime
R - the type of the merged value as returned by merge(MergingValue, MergingValue)
All Superinterfaces:
DataSerializable
All Known Implementing Classes:
com.hazelcast.spi.impl.merge.AbstractSplitBrainMergePolicy, DiscardMergePolicy, ExpirationTimeMergePolicy, HigherHitsMergePolicy, HyperLogLogMergePolicy, LatestAccessMergePolicy, LatestUpdateMergePolicy, PassThroughMergePolicy, PutIfAbsentMergePolicy
public interface SplitBrainMergePolicy<V,T extends MergingValue<V>,R> extends DataSerializable
Policy for merging data structure values after a split-brain has been healed.

The values of merging and existing MergingValues are always in the in-memory format of the backing data structure. This can be a serialized format, so the content cannot be processed without deserialization. For most merge policies this will be fine, since the key or value are not used.

The deserialization is not done eagerly for two main reasons:

  • The deserialization is quite expensive and should be avoided, if the result is not needed.
  • There is no need to locate classes of stored entries on the server side, when the entries are not deserialized. So you can put entries from a client by using InMemoryFormat.BINARY with a different classpath on client and server. In this case a deserialization could throw a ClassNotFoundException.
If you need the deserialized data you can call MergingValue.getDeserializedValue() or MergingEntry.getKey(), which will deserialize the data lazily.

A merge policy can implement HazelcastInstanceAware to get the HazelcastInstance injected. This can be used to retrieve the user context via HazelcastInstance.getUserContext(), which is an easy way to get user dependencies that are otherwise hard to obtain.

A merge policy can also implement NodeAware to get an instance of Node injected.

Since:
3.10

  • Method Summary

    Modifier and Type
    Method
    Description
    R
    merge(T mergingValue, T existingValue)
    Selects the value of either the merging or the existing MergingValue which should be merged.

    Methods inherited from interface com.hazelcast.nio.serialization.DataSerializable

    readData, writeData

  • Method Details

    • merge

      R merge(T mergingValue, T existingValue)
      Selects the value of either the merging or the existing MergingValue which should be merged.

      Note that the existing MergingValue instance may be null if no matching data could be found to the merging MergingValue.

      Parameters:
      mergingValue - MergingValue instance that has the merging data of the smaller sub-cluster
      existingValue - MergingValue instance that has the existing data or null if no matching data exists
      Returns:
      the selected value for merging