Azure service bus subscription and topic size

Question

I have a ASB topic into which I publish a lot of messages. There will be multiple subscriptions to that topic. I am trying to find out if the subscription size will lead to an increase in topic size. That is, if there is 1 subscription then the topic size is same as the sum of message sizes in that subscription. If there are 2 subscriptions then the topic size becomes 2 times so on and so forth?

I am not looking to scale the topic. I already use a partitioned topic. What I am trying to figure out is if I send 50 messages to a topic and the topic has 4 subscriptions then will the size of the topic be the sum total of all the subscriptions messages? Or topics size will remain the sum total of all the message sizes withing the topic irrespective of the number of subscriptions it has?

Answer 1

The messages seem to be duplicated, so the sum of all subscriptions is counted towards the quota.

This is what the architecture says: https://azure.microsoft.com/en-us/documentation/articles/service-bus-queues-topics-subscriptions/

A topic subscription resembles a virtual queue that receives copies of the messages that are sent to the topic. Messages are received from a subscription identically to the way they are received from a queue.

So sending 1 message (10Kb) to 3 subscriptions, will cost 30KB from the quota

According to the billing FAQ you pay per operation:https://azure.microsoft.com/en-us/pricing/details/service-bus/

Multiple deliveries of the same message (for example, message fan out to multiple subscribers or message retrieval after abandon, deferral, or dead lettering) will be counted as independent operations. For example, in the case of a topic with three subscriptions, a single 64KB message sent and subsequently received will generate four billable operations, one “in” plus three “out”, assuming all messages are delivered to all subscriptions and deleted during the read.