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Would solace topic be created only if it has an active subscriber?

I am not an expert on Solace, so apologies if my question is a primitive.

I have inherited a code base that I am looking to get to know more. It uses solace for messaging purposes. I see that the application publishes messages to a topic. When I look up for this topic in solace UI I dont see the topic under the VPN.

  1. Would topics in solace be created only if there are active subscribers?
  2. I checked the logs of my application and they don't error out for the absence of the topic? What happens in case point 1 is true, and my application tries to send a message to solace when the topic hasnt been created.
  3. I am using SolAdmin 7.1.1.158, is there way I can see my topic even if it does not have an active subscriber? Should that matter?

Thanks

Solution

  • I believe that you are confused about what is a topic.

    Think of a topic as a concept of the publish-subscribe (pub/sub) architectural pattern. They are used to route data or events (in the form of messages) between distributed applications, often using a message broker or an event broker.

    Solace has a very detailed description of how topics work at https://solace.com/blog/solace-topics-vs-kafka-topics/. Do note that topics are not the same as topic-endpoints.

    Would topics in solace be created only if there are active subscribers?

    Topics are only concepts and can't really be "created".

    It is part of a message and used for routing messages. A application can also subscribe to a topic to receive messages that are published on a matching topic.

    I checked the logs of my application and they don't error out for the absence of the topic? What happens in case point 1 is true, and my application tries to send a message to solace when the topic hasnt been created.

    Publishers and consumers are decoupled when using the message broker.

    When there are no subscribers to a topic, messages will be discarded and the "no subscription match" statistics and logs will increment.

    If the publisher is sending guaranteed messages, you can enable the "Reject Msg To Sender On No Subscription Match" flag on it's client-profile to receive an negative acknowledgement when this occurs.

    I am using SolAdmin 7.1.1.158, is there way I can see my topic even if it does not have an active subscriber? Should that matter?

    Go to "Logging & Diagnostics" tab and select the "No Subscription Match Logs" view to take a look at the most recent messages that were dropped because there are no subscribers.