21 Topic Configurations by Example

You can learn how to configure Coherence topics by reviewing a series of sample topic scheme definitions that can be used or modified as required.See Configuring Topics for detailed instructions on how to configure topics.

This chapter contains the following sections:

  • Define a Durable Subscriber Group
    The example below shows how to statically configure a durable subscriber-group durable-subscription for topic topicWithDurableSubscription. One can define none, one, or many subscriber groups for a topic. All values published to topic topicWithDurableSubscription will be accumulated for this subscriber group.
  • Configuring Value Expiry and Upper Bound on Storage Used for Values Retained for a Topic
    The following example illustrates how to parameterize a paged-topic-scheme element so that it can be configured via topic-mapping user-defined parameter macros.
  • Configuring a Persistent Topic
    If persistence is enabled on a topic and the entire cluster is restarted, the outstanding unconsumed values on the topic for subscribers, and subscriber group(s) are recovered during persistence recovery operations.

Parent topic: Using Topics

Define a Durable Subscriber Group

The example below shows how to statically configure a durable subscriber-group durable-subscription for topic topicWithDurableSubscription. One can define none, one, or many subscriber groups for a topic. All values published to topic topicWithDurableSubscription will be accumulated for this subscriber group. 
<topic-mapping>
  <topic-name>topicWithDurableSubscription</topic-name>
  <scheme-name>topic-scheme</scheme-name>
  <value-type>java.lang.String</value-type>
  <subscriber-groups>
    <subscriber-group>
      <name>durable-subscription</name>
    </subscriber-group>
  </subscriber-groups>
</topic-mapping>

Note:

Since each value published to a topic is retained until all subscriber(s)/subscriber group(s) have consumed the value, it is important to actively manage subscriber groups. If a statically configured subscriber group is no longer necessary, remove it from the topic-mapping configuration file. The life cycle of statically configured and dynamically created subscriber groups should be manage as described in list subscriber groups and destroy subscriber group.

Parent topic: Topic Configurations by Example

Configuring Value Expiry and Upper Bound on Storage Used for Values Retained for a Topic

The following example illustrates how to parameterize a paged-topic-scheme element so that it can be configured via topic-mapping user-defined parameter macros.

See Using User-Defined Parameter Macros for details on how to use this feature with cache-mapping. The same usage model applies to topic-mapping.

In the example below, the paged-topic-scheme.configurable-topic-scheme.expiry-delay has a user-defined parameter macro default value of 0; thus, the default expiry for the topic values will be to never expire. The default high-units user-defined parameter macro value is 0B; thus, there is no storage limit for paged-type-scheme.configurable-topic-scheme unless the referring topic-mapping explicitly defines expiry-delay and high-units parameters. For this example, the topic-mapping.initial-params override both expiry-delay and high-units.

Example 21-1 Configure paged-topic-scheme using User-defined Parameter Macros

<cache-config>
   <topic-mapping-schemes>
     <topic-mapping>
        <name>topic</name>
        <scheme>configurable-topic-scheme</scheme>
        <initial-params>
          <init-param>
            <param-name>high-units</param-name>
            <param-value>2G<param-value>
          </init-param>
          <init-param>
            <param-name>expiry-delay</param-name>
            <param-value>12h<param-value>
          </init-param>
        </initial-params>
     <topic-mapping>
   <topic-mapping-scheme>
   <caching-schemes>
     <paged-topic-scheme>
       <scheme-name>configurable-topic-scheme</scheme-name>
       <service-name>DistributedTopicService</service-name>
       <storage>on-heap</storage>
       <expiry-delay>{expiry-delay 0}</expiry-delay>
       <high-units>{high-units 0B}</high-units>
    </paged-topic-scheme>
   <caching-schemes>
</cache-config>

Parent topic: Topic Configurations by Example

Configuring a Persistent Topic

If persistence is enabled on a topic and the entire cluster is restarted, the outstanding unconsumed values on the topic for subscribers, and subscriber group(s) are recovered during persistence recovery operations.

Below is a sample configuration that enables configuring persistent topics.

Example 21-2 Configuring transient and persistent topic-mappings with same topic scheme

<cache-config>
   <topic-mapping-schemes>
     <topic-mapping>
        <name>persistent-topic-*</name>
        <scheme>persistent-topic-scheme</scheme>
     <topic-mapping>
     <topic-mapping>
        <name>transient-topic-*</name>
        <scheme>persistent-topic-scheme</scheme>
	  <initial-params>
          <initial-param>
            <param-name>transient</param-name>
            <param-value>true</param-value>
          </initial-param>
         </initial-params>
     <topic-mapping>
   <topic-mapping-scheme>
   <caching-schemes>
     <paged-topic-scheme>
       <scheme-name>persistent-topic-scheme</scheme-name>
       <service-name>DistributedTopicService</service-name>
       <storage>on-heap</storage>
       <transient>{transient false}</transient>
       <persistence>
         <environment>default-active</environment>
       </persistence>
       <partitioned-quorum-policy-scheme>
	   <recover-quorum>{recover-quorum 0}</recover-quorum>
       <partitioned-quorum-policy-scheme>
       <autostart>true</autostart>
       <expiry-delay>{expiry-delay 0}</expiry-delay>
       <high-units>{high-units 0B}</high-units>
     </paged-topic-scheme>
   <caching-schemes>
</cache-config>

In Example 21-2, all topic names starting with prefix persistent-topic- are persistent topics. All topic names starting with prefix transient-topic- are transient topics. If paged-topic-scheme subelement transient is false and a persistence.environment is defined, the topic is persistent. When subelement transient is true, the unconsumed values of the topic is not recovered during persistence recovery operations when a cluster is completely restarted. This example uses one of the pre-defined persistence environments, default-active, for the value of paged-topic-scheme.persistence.environment. See Overview of the Pre-Defined Persistence Environment for details. Configuration of the recover-quorum subelement is discussed in Using Quorum for Persistence Recovery. If no value is provided for recover-quorum in a topic-mapping.initial-param, the default of 0 results in the predefined Using the Dynamic Recovery Quorum Policy being used.

Parent topic: Topic Configurations by Example