com.hazelcast.topic
Enum TopicOverloadPolicy

java.lang.Object
  java.lang.Enum<TopicOverloadPolicy>
      com.hazelcast.topic.TopicOverloadPolicy

All Implemented Interfaces:

Serializable, Comparable<TopicOverloadPolicy>

@Beta
public enum TopicOverloadPolicy
extends Enum<TopicOverloadPolicy>

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 HazelcastInstance.getReliableTopic(String). The reliable topic uses a 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 retention time can be set on the ringbuffer. See com.hazelcast.config.RingbufferConfig#setRetentionSeconds(int). This TopicOverloadPolicy controls how te 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.

Enum Constant Summary

BLOCK
The caller will wait till there space in the ringbuffer.

DISCARD_NEWEST
The message that was to be published, is discarded.

DISCARD_OLDEST
Using this policy a message that has not expired can be overwritten.

ERROR
The publish call immediately fails.

Method Summary

static TopicOverloadPolicy	valueOf(String name) Returns the enum constant of this type with the specified name.
static TopicOverloadPolicy[]	values() Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

DISCARD_OLDEST

public static final TopicOverloadPolicy DISCARD_OLDEST

Using this policy a message that has not expired can be overwritten. So no matter the retention period set, the overwrite will just overwrite the item. This can be a problem for the slow consumer because he was promised a certain time window to process messages. But it will benefit producers and fast consumers since they are able to continue. So this policy sacrifices the slow producer in favor of fast producers/consumers.

DISCARD_NEWEST

public static final TopicOverloadPolicy DISCARD_NEWEST

The message that was to be published, is discarded.

BLOCK

public static final TopicOverloadPolicy BLOCK

The caller will wait till there space in the ringbuffer.

ERROR

public static final TopicOverloadPolicy ERROR

The publish call immediately fails.

Method Detail

values

public static TopicOverloadPolicy[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (TopicOverloadPolicy c : TopicOverloadPolicy.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static TopicOverloadPolicy valueOf(String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

IllegalArgumentException - if this enum type has no constant with the specified name

NullPointerException - if the argument is null