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7.8. Queues

Queues are named entities that hold/buffer messages for later delivery to consumer applications.

Queues can be managed using the HTTP or AMQP channels.

7.8.1. Types

The Broker supports four different queue types, each with different delivery semantics.

  • Standard - a simple First-In-First-Out (FIFO) queue

  • Priority - delivery order depends on the priority of each message

  • Sorted - delivery order depends on the value of the sorting key property in each message

  • Last Value Queue - also known as an LVQ, retains only the last (newest) message received with a given LVQ key value

7.8.2. Attributes

  • Name of the queue. Message consumers and browsers refer to this name when they wish to subscribe to queue to receive messages from it.

  • Type of the queue. Can be either standard, priority, sorted, or lvq.

  • Durable. Whether the queue survives a restart. Messages on a non durable queue do not survive a restart even if they are marked persistent.

  • Maximum/Minimum TTL. Defines a maximum and minimum time-to-live. Messages arriving with ttl larger than the maximum will be overridden by the maximum. Similarly, messages arriving with tll less than the minimum (or no ttl at all), will be overridden by the minimum.

    Changing these values affects only new arrivals, existing messages already on the queue are not affected.

  • Message persistent override. Allow message persistent settings of incoming messages to be overridden. Changing this value affects only new arrivals, existing messages on the queue are not affected.

  • Queue capacity. Queues have the ability to limit the of the cumulative size of all the messages contained within the store. This feature is described in detail Section 9.2, “Disk Space Management”.

  • Alerting Thresholds. Queues have the ability to alert on a variety of conditions: total queue depth exceeded a number or size, message age exceeded a threshold, message size exceeded a threshold. These thresholds are soft. See Appendix D, Queue Alerts

  • Maximum Delivery Count/Alternate Exchange. See Section 9.4, “Handing Undeliverable Messages”

  • Message Groups. See Section 4.7.3, “Messaging Grouping”

7.8.3. Children

  • Binding

7.8.4. Lifecycle

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