A "retroactive" address is an address that will preserve messages sent to it for queues which will be created on it in the future. This can be useful in, for example, publish-subscribe use cases where clients want to receive the messages sent to the address before they they actually connected and created their multicast "subscription" queue. Typically messages sent to an address before a queue was created on it would simply be unavailable to those queues, but with a retroactive address a fixed number of messages can be preserved by the broker and automatically copied into queues subsequently created on the address. This works for both anycast and multicast queues.
Internal Retroactive Resources
To implement this functionality the broker will create 4 internal resources for each retroactive address:
- A non-exclusive divert to grab the messages from the retroactive address.
- An address to receive the messages from the divert.
- Two ring queues to hold the messages sent to the address by the divert - one for anycast and one for multicast. The general caveats for ring queues still apply here. See the chapter on ring queues for more details.
These resources are important to be aware of as they will show up in the web console and other management or metric views. They will be named according to the following pattern:
For example, if an address named
myAddress had a
of 10 and the default
the default delimiter (i.e.
.) were being used then resources with these names
would be created:
- A divert on
- An address named
- A multicast queue on the address from step #2 named
- An anycast queue on the address from step #2 named
This pattern is important to note as it allows one to configure address-settings if necessary. To configure custom address-settings you'd use a match like:
Using the same example as above the
match would be:
Changing the broker's
internal-naming-prefixonce these retroactive resources are created will break the retroactive functionality.
To configure an address to be "retroactive" simply configure the
address-setting to reflect the number of messages
you want the broker to preserve, e.g.:
<address-settings> <address-setting match="orders"> <retroactive-message-count>100</retroactive-message-count> </address-setting> </address-settings>
The value for
retroactive-message-count can be updated at runtime either via
broker.xml or via the management API just like any other address-setting.
However, if you reduce the value of
retroactive-message-count an additional
administrative step will be required since this functionality is implemented
via ring queues. This is because a ring queue whose ring-size is reduced will
not automatically delete messages from the queue to meet the new ring-size in
order to avoid unintended message loss. Therefore, administrative action will
be required in this case to manually reduce the number of messages in the ring
queue via the management API.