# Message Expiry

Messages can be set with an optional time to live when sending them.

Apache ActiveMQ Artemis will not deliver a message to a consumer after it's time to live has been exceeded. If the message hasn't been delivered by the time that time to live is reached the server can discard it.

Apache ActiveMQ Artemis's addresses can be assigned an expiry address so that, when messages are expired, they are removed from the queue and sent to the expiry address. Many different queues can be bound to an expiry address. These expired messages can later be consumed for further inspection.

## Core API

Using Apache ActiveMQ Artemis Core API, you can set an expiration time directly on the message:

    // message will expire in 5000ms from now
    message.setExpiration(System.currentTimeMillis() + 5000);

JMS MessageProducer allows to set a TimeToLive for the messages it sent:

    // messages sent by this producer will be retained for 5s (5000ms) before expiration
    producer.setTimeToLive(5000);

Expired messages get special properties plus this additional property:

- `_AMQ_ACTUAL_EXPIRY`

  a Long property containing the actual expiration time of the expired message

## Configuring Expiry Delay

Default expiry delay can be configured in the address-setting configuration:

    <!-- expired messages in exampleQueue will be sent to the expiry address expiryQueue -->
    <address-setting match="exampleQueue">
       <expiry-address>expiryQueue</expiry-address>
       <expiry-delay>10</expiry-delay>
    </address-setting>

`expiry-delay` defines the expiration time in milliseconds 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. 10) 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`.

If `expiry-delay` is not set then minimum and maximum expiry delay values can be configured in the address-setting configuration.

    <address-setting match="exampleQueue">
       <min-expiry-delay>10</min-expiry-delay>
       <max-expiry-delay>100</max-expiry-delay>
    </address-setting>

Semantics are as follows:

- Messages without an expiration will be set to `max-expiry-delay`. If `max-expiry-delay` is not defined then the message will be set to `min-expiry-delay`. If `min-expiry-delay` is not defined then the message will not be changed.
- Messages with an expiration above `max-expiry-delay` will be set to `max-expiry-delay`
- Messages with an expiration below `min-expiry-delay` will be set to `min-expiry-delay`
- Messages with an expiration within `min-expiry-delay` and `max-expiry-delay` range will not be changed
- Any value set for `expiry-delay` other than the default (i.e. `-1`) will override the aforementioned min/max settings.

The default for both `min-expiry-delay` and `max-expiry-delay` is `-1` (i.e. disabled).

## Configuring Expiry Addresses

Expiry address are defined in the address-setting configuration:

    <!-- expired messages in exampleQueue will be sent to the expiry address expiryQueue -->
    <address-setting match="exampleQueue">
       <expiry-address>expiryQueue</expiry-address>
    </address-setting>

If messages are expired and no expiry address is specified, messages are simply removed from the queue and dropped. Address wildcards can be used to configure expiry address for a set of addresses.

## Configuring Automatic Creation of Expiry Resources

It's common to segregate expired messages by their original address. For example, a message sent to the `stocks` address that expired for some reason might be ultimately routed to the `EXP.stocks` queue, and likewise a message sent to the `orders` address that expired might be routed to the `EXP.orders` queue.

Using this pattern can make it easy to track and administrate expired messages. However, it can pose a challenge in environments which predominantly use auto-created addresses and queues. Typically administrators in those environments don't want to manually create an `address-setting` to configure the `expiry-address` much less the actual `address` and `queue` to hold the expired messages.

The solution to this problem is to set the `auto-create-expiry-resources` `address-setting` to `true` (it's `false` by default) so that the broker will create the `address` and `queue` to deal with the expired messages automatically. The `address` created will be the one defined by the `expiry-address`. A `MULTICAST` `queue` will be created on that `address`. It will be named by the `address` to which the message was previously sent, and it will have a filter defined using the property `_AMQ_ORIG_ADDRESS` so that it will only receive messages sent to the relevant `address`. The `queue` name can be configured with a prefix and suffix. See the relevant settings in the table below:

`address-setting` | default
--- | ---
`expiry-queue-prefix` | `EXP.`
`expiry-queue-suffix` | (empty string)

Here is an example configuration:

    <address-setting match="#">
       <expiry-address>expiryAddress</expiry-address>
       <auto-create-expiry-resources>true</auto-create-expiry-resources>
       <expiry-queue-prefix></expiry-queue-prefix> <!-- override the default -->
       <expiry-queue-suffix>.EXP</expiry-queue-suffix>
    </address-setting>

The queue holding the expired messages can be accessed directly either by using the queue's name by itself (e.g. when using the core client) or by using the fully qualified queue name (e.g. when using a JMS client) just like any other queue. Also, note that the queue is auto-created which means it will be auto-deleted as per the relevant `address-settings`.

## Configuring The Expiry Reaper Thread

A reaper thread will periodically inspect the queues to check if messages have expired.

The reaper thread can be configured with the following properties in `broker.xml`

- `message-expiry-scan-period`

  How often the queues will be scanned to detect expired messages (in milliseconds, default is 30000ms, set to `-1` to disable the reaper thread)

## Example

See the Message Expiration Example which shows how message expiry is configured and used with JMS.

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