com.hazelcast.partition.PartitionAware Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2024, Hazelcast, Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hazelcast.partition;
/**
* PartitionAware means that data will be based in the same member based on the partition key
* and implementing tasks will be executed on the {@link #getPartitionKey()}'s owner member.
*
* This achieves data affinity. Data and execution occurs on the same partition.
*
* In Hazelcast, disparate data structures will be stored on the same partition,
* based on the partition key. For example, if "Steve" was used, then the following would be on one partition.
*
* - a customers IMap with an entry of key "Steve"
*
- an orders IMap using a customer key type implementing PartitionAware with key "Steve"
*
- any queue named "Steve"
*
- any PartitionAware object with partition key "Steve"
*
*
* If you have a {@link com.hazelcast.core.IExecutorService} which needs to deal with a customer and a customer's
* orders, you can achieve optimal performance by putting them on the same partition.
*
* {@link com.hazelcast.core.DistributedObject} also has a notion of the partition key which is of type String
* to ensure that the same partition as distributed Objects Strings is used for the partition key.
*
* @see com.hazelcast.core.DistributedObject
* @param key type
*/
@FunctionalInterface
public interface PartitionAware {
/**
* The key that will be used by Hazelcast to specify the partition.
* You should give the same key for objects that you want to be in the same partition.
*
* The contract of {@link #getPartitionKey()} method is as follows:
*
* Let us define {@code toData(o)} as serialized form of given object obtained by using
* Hazelcast Serialization configured for the cluster (the exact method used is
* {@link com.hazelcast.internal.serialization.SerializationService#toData SerializationService.toData}
* from an internal SPI).
*
* Assume {@code PartitionAware a, b} are objects (e.g. IMap keys) and
* {@code T pk1 = a.getPartitionKey(), pk2 = b.getPartitionKey()} are partition key values.
*
* Then {@link #getPartitionKey()} implementation must obey the following contract:
*
* - (mandatory) Deterministic partitioning: if {@code a.equals(b)} then either
* {@code toData(a.getPartitionKey()).equals(toData(b.getPartitionKey()))}
* or {@code a.getPartitionKey() == null && b.getPartitionKey() == null}
* - (recommended) Reasonable partitioning: if {@code a.equals(b)} then
* {@code a.getPartitionKey().equals(b.getPartitionKey())}
* - (recommended) Reasonable partitioning key serialization (if custom
* serialization is used): if {@code pk1.equals(pk2)} then
* {@code toData(pk1).equals(toData(pk2))}
* - The above stated conditions must hold when the {@link #getPartitionKey()}
* is invoked any number of times on any member or client, regardless of time
* (note that some partitioned data structures support persistence) and if the JVM
* is restarted, regardless of client/member version and JVM version (across all JVMs
* ever used in given deployment), timezone, locale and similar differences in the
* environment.
*
* Adhering to the contract guarantees stable partitioning of the data and ability to find
* appropriate member and partition who owns given object during querying and modifications.
*
* Notes:
*
* - {@link #getPartitionKey()} contract is similar to {@link Object#hashCode() hashCode()}
* but with stricter long-term requirements.
* - Partition key is not compared directly, only serialized form is compared or used to
* calculate partition id.
* - For unequal objects {@link #getPartitionKey()} may return the same or different values
* according to specific partitioning use case needs.
*
*
* @return the key that specifies the partition. Returning {@code null} or {@code this} will
* cause the result as if the object did not implement {@link PartitionAware}. If the
* returned key itself implements {@link PartitionAware}, this fact will be ignored
* and the key will be treated as a plain object.
*/
T getPartitionKey();
}