# Three teams. One queue. Everyone missed messages.

> A queue is a DM. A topic is the group broadcast. The difference is a real bug.

- **Format:** short video, 10 steps, ~32 seconds
- **Topic:** Point-to-point or publish/subscribe — why three teams on one Service Bus queue all end up with a third of the messages.
- **Author:** Suthahar Jegatheesan (MSDEVBUILD)
- **Category:** Azure · Azure
- **Tags:** azure, azureservicebus, pubsub, servicebus, messagequeue, eventdrivenarchitecture, systemdesign, microsoftazure, azurecloud, cloudarchitecture, microservices, az305, msdevbuild
- **Canonical URL:** https://blog.msdevbuild.com/shorts/azure-pubsub-vs-point-to-point/

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## What you'll learn

- Why three teams on one queue each get a third of the messages
- How competing consumers differ from real subscribers
- What a subscription gives you that a second reader never will

## Understand it one step at a time

### 1. One message. Who gets it?

Billing, analytics and audit all need to know an order was placed. All three are listening.

### 2. A queue is a DM

Exactly one consumer receives each message, completes it, and it is deleted. Nobody else sees it.

### 3. Add a second consumer

The other teams attach to the same queue expecting a copy. Instead all three start competing.

### 4. That's scale, not fan-out

Competing consumers exist to go faster, not to go wider. It is the right tool for the wrong goal here.

### 5. A topic is a group broadcast

Same message, same sender code. The topic hands a private copy to every subscription.

### 6. Each subscription is its own queue

Its own backlog, its own delivery count, its own dead-letter queue. One broken reader hurts nobody else.

### 7. Filters let you mute

A subscription rule decides which messages it even receives — like muting the parts of the group you ignore.

### 8. One line of difference

The sender does not change at all. A topic is addressed exactly like a queue — the fan-out is infrastructure.

### 9. Queue or topic

One is work that must happen once. The other is news that several teams need to hear.

### 10. One reader? Queue. Many? Topic.

And if you are not sure yet, a topic with one subscription costs almost nothing and saves the migration.

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## The takeaway

**Competing consumers are not subscribers**

Adding a reader to a queue divides the work. Adding a subscription duplicates the message.