Controlling retention of publication

1. A method of controlling the retention of publications in a publish/subscribe system, the method comprising:

receiving, at a message broker, a first publication from a publisher on a topic, wherein the message broker includes a processor;

receiving, at the message broker, a second publication from the publisher on the topic;

identifying, at the message broker, whether the first publication should be overwritten with the second publication and, if not, retaining at least payload data from both the first and second publications on the topic;

storing, for the second publication, if retained, history data indicating when the second publication was published to the broker in a common message with the payload data for the second publication;

storing, using the message broker, data indicating when the first publication was last accessed by a subscriber, data indicating when the second publication was last accessed by a subscriber, data indicating the number of times the first publication was accessed by a subscriber, and data indicating the number of times the second publication was accessed by a subscriber; and

selectively removing a publication in response to at least one of number of times accessed and time when last accessed.

2. The method in accordance with claim 1 and further comprising overwriting, using the message broker, the first publication with the second publication if the identifying indicates that the first publication should be overwritten with the second publication.

3. The method in accordance with claim 1 and further comprising receiving, at the message broker, a more recent publication from the publisher on the topic, and accepting and responding to requests, using the message broker, from a subscriber for only the most recent publication on the topic, for all publications on the topic, or for a specific subset of publications on the topic.

4. A system controlling the retention of publications in a publish/subscribe system, the system comprising:

a computer comprising a processor; and

instructions which are executable, using the processor, to perform functions comprising:

receiving, at a message broker, a first publication from a publisher on a topic;

receiving, at the message broker, a second publication from the publisher on the topic;

identifying, at the message broker, whether the first publication should be overwritten with the second publication and, if not, retaining at least payload data from both the first and second publications on the topic;

storing, for the second publication, if retained, history data indicating when the second publication was published to the broker in a common message with the payload data for the second publication;

storing, using the message broker, data indicating when the first publication was last accessed by a subscriber, data indicating when the second publication was last accessed by a subscriber, data indicating the number of times the first publication was accessed by a subscriber, and data indicating the number of times the second publication was accessed by a subscriber; and

selectively removing a publication in response to at least one of number of times accessed and time when last accessed.

5. The system in accordance with claim 4 , wherein the functions further comprise overwriting, using the message broker, the first publication with the second publication if the identifying indicates that the first publication should be overwritten with the second publication.

6. The system in accordance with claim 4 , wherein the functions further comprise receiving, at the message broker, a more recent publication from the publisher on the topic, and accepting and responding to requests, using the message broker, from a subscriber for only the most recent publication on the topic, for all publications on the topic, or for a specific subset of publications on the topic.

7. A computer program product comprising a non-transitory computer usable storage medium having a computer readable program embodied therein, wherein the computer readable program, when executed on a computer, causes the computer to:

receive, at a message broker, a first publication from a publisher on a topic;

receive, at the message broker, a second publication from the publisher on the topic;

identify, at the message broker, whether the first publication should be overwritten with the second publication and, if not, retaining at least payload data from both the first and second publications on the topic;

store, for the second publication, if retained, history data indicating when the second publication was published to the broker in a common message with the payload data for the second publication;

store, using the message broker, data indicating when the first publication was last accessed by a subscriber, data indicating when the second publication was last accessed by a subscriber, data indicating the number of times the first publication was accessed by a subscriber, and data indicating the number of times the second publication was accessed by a subscriber; and

selectively remove a publication in response to at least one of number of times accessed and time when last accessed.

8. The computer program product in accordance with claim 7 , wherein the computer readable program further causes the computer to overwrite, using the message broker, the first publication with the second publication if the identifying indicates that the first publication should be overwritten with the second publication.

9. The computer program product in accordance with claim 7 , wherein the computer readable program further causes the computer to receive, at the message broker, a more recent publication from the publisher on the topic, and accepting and responding to requests, using the message broker, from a subscriber for only the most recent publication on the topic, for all publications on the topic, or for a specific subset of publications on the topic.