Configuring the Type of Cursor Used by a Destination

Overview

By default, FUSE Message Broker uses store-based cursors. You can, however, configure your destinations to use one of the alternative cursor implementations by adding the appropriate policy entries into the destination's policy map.

You configure a destination's policy set using a destinationPolicy element. The destinationPolicy element is a wrapper for a policyMap element. The policyMap element is a wrapper for a policyEntries element. The policyEntries element is a wrapper for one or more policyEntry elements.

The cursor policies are entered as children to a policyEntry element. The configuration elements used to specify the type of destination you are configuring. Topics use cursors for both durable subscribers and transient subscribers, so it uses two sets of configuration elements. Queues only a single cursor and only require a single set of configuration elements.

Configuring topics

Topics maintain a dispatch queue and a pending cursor for every consumer subscribed to the topic regardless of whether the subscription is durable or transient. You can configure the cursor implementation used by durable subscribers separately from the cursor implementation used by transient subscribers.

	Important
	If you want to use the store-based cursor implementation, you do not add any extra elements to the configuration. FUSE Message Broker uses store-based cursors by default.

You configure the cursor implementation used by durable subscribers by adding PendingDurableSubscriberMessageStoragePolicy child element to the topic's policyEntry element. Table 4.1 describes the possible children of PendingDurableSubscriberMessageStoragePolicy.

Table 4.1. Elements for Configuring the Type of Cursor to Use for Durable Subscribers

Element	Description
`vmDurableCursor`	Specifies the VM cursors will be used. See VM cursors for more information.
`fileDurableSubscriberCursor`	Specifies that file-based cursors will be used. See File-based cursors for more information.

You configure the cursor implementation used by transient subscribers by adding pendingSubscriberPolicy child element to the topic's policyEntry element. Table 4.2 describes the possible children of pendingSubscriberPolicy.

Table 4.2. Elements for Configuring the Type of Cursor to Use for Transient Subscribers

Element	Description
`vmCursor`	Specifies the VM cursors will be used. See VM cursors for more information.
`fileCursor`	Specifies that file-based cursors will be used. See File-based cursors for more information.

Example 4.1 shows a configuration snip-it that configures a topic to use VM cursors for its transient subscribers and file-based cursors for its durable subscribers.

Example 4.1. Configuring a Topic's Cursor Usage

<beans ... >
  <broker ...>
    ...
    <destinationPolicy>
      <policyMap>
        <policyEntries>
          <policyEntry topic="com.iona.>">
            ...
            <pendingSubscriberPolicy>
              <vmCursor />
            </pendingSubscriberPolicy>
            <PendingDurableSubscriberMessageStoragePolicy>
              <fileDurableSubscriberPolicy />
            </PendingDurableSubscriberMessageStoragePolicy>
            ...
          </policyEntry>
          ...
        </policyEntries>
      </policyMap>
    </destinationPolicy>
    ...
  </broker>
  ...
</beans>

Configuring queues

Queues use a single pending cursor and dispatch queue. You configure the type of cursor to use by adding a pendingQueuePolicy element to the queue's policyEntry element. Table 4.3 describes the possible children elements of the pendingQueuePolicy element.

Table 4.3. Elements for Configuring the Type of Cursor to Use for a Queue

Element	Description
`vmQueueCursor`	Specifies the VM cursors will be used. See VM cursors for more information.
`fileQueueCursor`	Specifies that file-based cursors will be used. See File-based cursors for more information.

Example 4.2 shows a configuration snip-it that configures a queue to use VM cursors.

Example 4.2. Configuring a Queue's Cursor Usage

<beans ... >
  <broker ...>
    ...
    <destinationPolicy>
      <policyMap>
        <policyEntries>
          <policyEntry queue="com.iona.>">
            ...
            <pendingQueuePolicy>
              <vmQueueCursor />
            </pendingQueuePolicy>
            ...
          </policyEntry>
          ...
        </policyEntries>
      </policyMap>
    </destinationPolicy>
    ...
  </broker>
  ...
</beans>