com.hazelcast.topic.TopicOverloadPolicy Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2016, 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.topic;
import com.hazelcast.spi.annotation.Beta;
/**
* A policy to deal with an overloaded topic; so topic where there is no place to store new messages.
*
* This policy can only be used in combination with the {@link com.hazelcast.core.HazelcastInstance#getReliableTopic(String)}.
*
* The reliable topic uses a {@link com.hazelcast.ringbuffer.Ringbuffer} to store the messages. A ringbuffer doesn't track where
* readers are, so therefore it has no concept of a slow consumers. This provides many advantages like high performance reads, but
* it also gives the ability to the reader to reread the same message multiple times in case of error.
*
* Because a ringbuffer has a capacity and to prevent that a fast producer overwrites the messages needed by a slow consumer, a
* time to live time can be set on the ringbuffer. See {@link com.hazelcast.config.RingbufferConfig#setTimeToLiveSeconds(int)}.
* This {@link TopicOverloadPolicy} controls how the publisher is going to deal with the situation that a ringbuffer is full
* and the oldest item in the ringbuffer is not old enough to get overwritten.
*
* So keep in mind that a this retention period keep the messages in memory, even though it might by that all readers already
* have completed reading.
*/
@Beta
public enum TopicOverloadPolicy {
/**
* Using this policy, a message that has not expired can be overwritten. No matter the retention period set, the overwrite
* will just overwrite the item.
*
* This can be a problem for slow consumers because they were promised a certain time window to process messages. But it will
* benefit producers and fast consumers since they are able to continue. This policy sacrifices the slow producer in favor
* of fast producers/consumers.
*/
DISCARD_OLDEST,
/**
* The message that was to be published, is discarded.
*/
DISCARD_NEWEST,
/**
* The caller will wait till there space in the ringbuffer.
*/
BLOCK,
/**
* The publish call immediately fails.
*/
ERROR
}