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7.2. Configuring the Type of Cursor Used by a Destination
Overview
By default, JBoss A-MQ uses store-based cursors for persistent messages and file-based cursors for non-persistent messages. You can, however, configure your destinations to use a specified cursor implementation 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.
You configure the cursor implementation used by durable subscribers by adding
PendingDurableSubscriberMessageStoragePolicy child element to the topic's policyEntry element. Table 7.1, “Elements for Configuring the Type of Cursor to Use for Durable Subscribers” describes the possible children of PendingDurableSubscriberMessageStoragePolicy.
| Element | Description |
|---|---|
storeDurableSubscriberCursor | Specifies that store-based cursors will be used. See the section called “Store-based cursors” for more information. |
vmDurableCursor | Specifies that VM cursors will be used. See the section called “VM cursors” for more information. |
fileDurableSubscriberCursor | Specifies that file-based cursors will be used—only suitable for non-persistent messages. See the section called “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 7.2, “Elements for Configuring the Type of Cursor to Use for Transient Subscribers” describes the possible children of pendingSubscriberPolicy.
| Element | Description |
|---|---|
| Unspecified | Default policy is to use store-based cursors. See the section called “Store-based cursors” for more information. |
vmCursor | Specifies the VM cursors will be used. See the section called “VM cursors” for more information. |
fileCursor | Specifies that file-based cursors will be used. See the section called “File-based cursors” for more information. |
Example 7.1, “Configuring a Topic's Cursor Usage” 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 7.1. Configuring a Topic's Cursor Usage
<beans ... >
<broker ... >
...
<destinationPolicy>
<policyMap>
<policyEntries>
<policyEntry topic="com.fusesource.>" >
...
<pendingSubscriberPolicy>
<vmCursor />
</pendingSubscriberPolicy>
<pendingDurableSubscriberPolicy>
<storeDurableSubscriberCursor />
</pendingDurableSubscriberPolicy>
...
</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 7.3, “Elements for Configuring the Type of Cursor to Use for a Queue” describes the possible children elements of the pendingQueuePolicy element.
| Element | Description |
|---|---|
storeCursor | Specifies that store-based cursors will be used. See the section called “Store-based cursors” for more information. |
vmQueueCursor | Specifies the VM cursors will be used. See the section called “VM cursors” for more information. |
fileQueueCursor | Specifies that file-based cursors will be used. See the section called “File-based cursors” for more information. |
Example 7.2, “Configuring a Queue's Cursor Usage” shows a configuration snippet that configures a queue to use VM cursors.
Example 7.2. Configuring a Queue's Cursor Usage
<beans ... >
<broker ... >
...
<destinationPolicy>
<policyMap>
<policyEntries>
<policyEntry queue="com.fusesource.>" >
...
<pendingQueuePolicy>
<vmQueueCursor />
</pendingQueuePolicy>
...
</policyEntry>
...
</policyEntries>
</policyMap>
</destinationPolicy>
...
</broker>
...
</beans>