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What will happen to messages posted to a virtual topic when there are no consumers listening ? Will the broker hold them for a certain while until a subscriber is available ?
More specifically :
At T0 and T1 messages M0 and M1 are posted. At T2, consumer C1 connects, will he receive M0 and M1 ? Obviously messages M2 and M3 posted at T3 and T4 will be received by C1, but what will a new Consumer, C2, that connects at T5 receice ? All messages, M2 and M3, or none ?
It depends on the nature of the topic:
if the topic is durable (has durable consumers subscribing to it), the broker will hold the messages in the topic until all the durable consumers consumes the messages.
if the topic is non-durable (no durable consumers), the message will not even be sent to the topic, as there will be no durable subscription.
For your example, I’ll consider that you are using durable subscriptions / consumers:
Case 1:
That’s because they are holding durable subscriptions
You need to be very careful when using durable topics / queues: if the consumer doesn’t unsubscribe, the broker will hold the messages until the message store explodes. You will need to make sure it doesn’t happen (by setting eviction policies and / or putting a Time to Live on the messages).
Of course the previous example will vary depending when the consumer does the durable subscription.
If you are using non-durable topics: