# Queue Attributes

Queue attributes can be set in one of two ways. Either by configuring them using the configuration file or by using the core API. This chapter will explain how to configure each attribute and what effect the attribute has.

## Predefined Queues

Queues can be predefined via configuration at a core level or at a JMS level. Firstly let's look at a JMS level.

The following shows a queue predefined in the jms element of the `broker.xml` configuration file.

    <queue name="selectorQueue">
       <selector string="color='red'"/>
       <durable>true</durable>
    </queue>

This name attribute of queue defines the name of the queue. When we do this at a jms level we follow a naming convention so the actual name of the core queue will be `jms.queue.selectorQueue`.

The selector element defines what JMS message selector the predefined queue will have. Only messages that match the selector will be added to the queue. This is an optional element with a default of null when omitted.

The durable element specifies whether the queue will be persisted. This again is optional and defaults to true if omitted.

Secondly a queue can be predefined at a core level in the `broker.xml` file. The following is an example.

    <queues>
       <queue name="jms.queue.selectorQueue">
          <address>jms.queue.selectorQueue</address>
          <filter string="color='red'"/>
          <durable>true</durable>
        </queue>
    </queues>

This is very similar to the JMS configuration, with 3 real differences which are.

1. The name attribute of queue is the actual name used for the queue with no naming convention as in JMS.

2. The address element defines what address is used for routing messages.

3. The filter uses the Core filter syntax (described in filter Expressions), not the JMS selector syntax.

## Using the API

Queues can also be created using the core API or the management API.

For the core API, queues can be created via the `org.apache.activemq.artemis.api.core.client.ClientSession` interface. There are multiple `createQueue` methods that support setting all of the previously mentioned attributes. There is one extra attribute that can be set via this API which is `temporary`. setting this to true means that the queue will be deleted once the session is disconnected.

Take a look at Management for a description of the management API for creating queues.

## Configuring Queues Via Address Settings

There are some attributes that are defined against an address wildcard rather than a specific queue. Here an example of an `address-setting` entry that would be found in the `broker.xml` file.

    <address-settings>
       <address-setting match="jms.queue.exampleQueue">
          <dead-letter-address>jms.queue.deadLetterQueue</dead-letter-address>
          <max-delivery-attempts>3</max-delivery-attempts>
          <redelivery-delay>5000</redelivery-delay>
          <expiry-address>jms.queue.expiryQueue</expiry-address>
          <last-value-queue>true</last-value-queue>
          <max-size-bytes>100000</max-size-bytes>
          <page-size-bytes>20000</page-size-bytes>
          <redistribution-delay>0</redistribution-delay>
          <send-to-dla-on-no-route>true</send-to-dla-on-no-route>
          <address-full-policy>PAGE</address-full-policy>
          <slow-consumer-threshold>-1</slow-consumer-threshold>
          <slow-consumer-policy>NOTIFY</slow-consumer-policy>
          <slow-consumer-check-period>5</slow-consumer-check-period>
          <auto-create-jms-queues>true</auto-create-jms-queues>
          <auto-delete-jms-queues>true</auto-delete-jms-queues>
          <auto-create-jms-topics>true</auto-create-jms-topics>
          <auto-delete-jms-topics>true</auto-delete-jms-topics>
       </address-setting>
    </address-settings>

The idea with address settings, is you can provide a block of settings which will be applied against any addresses that match the string in the `match` attribute. In the above example the settings would only be applied to any addresses which exactly match the address `jms.queue.exampleQueue`, but you can also use wildcards to apply sets of configuration against many addresses. The wildcard syntax used is described here.

For example, if you used the `match` string `jms.queue.#` the settings would be applied to all addresses which start with `jms.queue.` which would be all JMS queues.

The meaning of the specific settings are explained fully throughout the user manual, however here is a brief description with a link to the appropriate chapter if available.

`max-delivery-attempts` defines how many time a cancelled message can be redelivered before sending to the `dead-letter-address`. A full explanation can be found here.

`redelivery-delay` defines how long to wait before attempting redelivery of a cancelled message. see here.

`expiry-address` defines where to send a message that has expired. see here.

`expiry-delay` defines the expiration time that will be used for messages which are using the default expiration time (i.e. 0). For example, if `expiry-delay` is set to "10" and a message which is using the default expiration time (i.e. 0) arrives then its expiration time of "0" will be changed to "10." However, if a message which is using an expiration time of "20" arrives then its expiration time will remain unchanged. Setting `expiry-delay` to "-1" will disable this feature. The default is "-1".

`last-value-queue` defines whether a queue only uses last values or not. see here.

`max-size-bytes` and `page-size-bytes` are used to set paging on an address. This is explained here.

`redistribution-delay` defines how long to wait when the last consumer is closed on a queue before redistributing any messages. see here.

`send-to-dla-on-no-route`. If a message is sent to an address, but the server does not route it to any queues, for example, there might be no queues bound to that address, or none of the queues have filters that match, then normally that message would be discarded. However if this parameter is set to true for that address, if the message is not routed to any queues it will instead be sent to the dead letter address (DLA) for that address, if it exists.

`address-full-policy`. This attribute can have one of the following values: PAGE, DROP, FAIL or BLOCK and determines what happens when an address where `max-size-bytes` is specified becomes full. The default value is PAGE. If the value is PAGE then further messages will be paged to disk. If the value is DROP then further messages will be silently dropped. If the value is FAIL then further messages will be dropped and an exception will be thrown on the client-side. If the value is BLOCK then client message producers will block when they try and send further messages. See the following chapters for more info Flow Control, Paging.

`slow-consumer-threshold`. The minimum rate of message consumption allowed before a consumer is considered "slow." Measured in messages-per-second. Default is -1 (i.e. disabled); any other valid value must be greater than 0.

`slow-consumer-policy`. What should happen when a slow consumer is detected. `KILL` will kill the consumer's connection (which will obviously impact any other client threads using that same connection). `NOTIFY` will send a CONSUMER_SLOW management notification which an application could receive and take action with. See slow consumers for more details on this notification.

`slow-consumer-check-period`. How often to check for slow consumers on a particular queue. Measured in seconds. Default is 5. See slow consumers for more information about slow consumer detection.

`auto-create-jms-queues`. Whether or not the broker should automatically create a JMS queue when a JMS message is sent to a queue whose name fits the address `match` (remember, a JMS queue is just a core queue which has the same address and queue name) or a JMS consumer tries to connect to a queue whose name fits the address `match`. Queues which are auto-created are durable, non-temporary, and non-transient. Default is `true`.

`auto-delete-jms-queues`. Whether or not the broker should automatically delete auto-created JMS queues when they have both 0 consumers and 0 messages. Default is `true`.

`auto-create-jms-topics`. Whether or not the broker should automatically create a JMS topic when a JMS message is sent to a topic whose name fits the address `match` (remember, a JMS topic is just a core address which has one or more core queues mapped to it) or a JMS consumer tries to subscribe to a topic whose name fits the address `match`. Default is `true`.

`auto-delete-jms-topics`. Whether or not the broker should automatically delete auto-created JMS topics once the last subscription on the topic has been closed. Default is `true`.

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