Conflated Topics

AMPS provides the ability for the server to conflate updates to a SOW topic by defining a conflated topic for that SOW topic.

A conflated topic will retain messages published to the underlying topic for a certain period of time, and provide the latest update for each distinct message in the underlying topic at the end of that period of time. In effect, AMPS guarantees that a subscriber will receive no more than one update for a given message per conflation interval.

A conflated topic provides a way to reduce the bandwidth and processing for subscribers in cases where the subscriber needs periodic updates with the current state of the message rather than a rapid set of updates with each individual change to the message.

For example, an application that presents a user interface to display rapidly changing data often uses conflation, since the value of a record may change more rapidly than the user interface is able to be refreshed. For this application, creating a conflated topic and then having the application subscribe to that topic can reduce network traffic, reduce processing load, and provide a more responsive user interface than if the application were to subscribe to the underlying topic and try to process every update.

AMPS provides the ability to conflate messages for an individual subscription, as described in the Conflated Subscriptions section. When a single subscriber requires conflation, requesting conflation for that subscription is a reasonable approach to take. In cases where all instances of an application can benefit from conflation, conflated topics are a more efficient and scalable approach. A conflated topic is a copy of one SOW topic into another with the ability to control the update interval. In this case, AMPS maintains conflation for the entire topic. There is no need for subscribers to independently request conflation, and AMPS does not need to spend resources processing conflation for each subscriber individually.

The underlying topic for a conflated topic can be a Topic, a View, or another ConflatedTopic.

To better see the value in a conflated topic, imagine a SOW topic called ORDER_STATE exists in an AMPS instance. ORDER_STATE messages are published frequently to the topic. Meanwhile, there are several subscribing clients that are watching updates to this topic and displaying the latest state in a GUI front-end.

If this GUI front-end only needs updates in five second intervals from the ORDER_STATE topic, then more frequent updates would be wasteful of network and client-side processing resources. To reduce network congestion, a conflated topic for the ORDER_STATE topic can be created which will contain a copy of ORDER_STATE updated in five second intervals. Only the changed records from ORDER_STATE will be copied to the conflated topic and then sent to the subscribing clients. Those records with multiple updates within the time interval will have their latest updated values copied to the conflated topic, and only those conflated values are sent to the clients. This results in substantial savings in bandwidth for records with high update rates. This can also result in substantial savings in processing overhead for a client.

AMPS treats the conflated topic as a conflated version of the underlying topic. Applications cannot publish directly to the conflated topic. Likewise, AMPS does not recalculate the SOW key for messages delivered from the conflated topic: these messages have the same SOW key as the corresponding message in the underlying topic.

AMPS indexes conflated topics in the same way that it indexes the underlying topic in the SOW. When a query uses a given field, AMPS will automatically create a memo index for that field. A configuration can also declare one or more HashIndex indexes for a conflated topic.

AMPS uses the following conflation strategy:

• When a message arrives for a given key, if no message is already pending for that key, begin the conflation interval.

• If an update arrives during the conflation interval for a given key, replace the pending message with the update for a subscription, or merge the update into the pending message for a delta subscription. All of the metadata on the message is fully replaced.

• If the update is an oof notification, and the key has not previously been delivered to the subscription, note that the message should not be delivered.

• At the end of the conflation interval, deliver the current version of the message unless the current message is an oof that should not be delivered. Remove the message from the set of messages being conflated.

This means that, when conflation is used, the first update for a given key will arrive after the conflation interval. Further, the application must expect that any given update may be delayed by up to the conflation interval.

The SOW/ConflatedTopic section in the AMPS Configuration Reference shows the configuration of conflated topics.