Azure Service Bus Topics Sequence vs Sessions

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Azure Service Bus Topics Sequence vs Sessions

Abhay Pratap Singh 0

What exactly is the difference between retrieval order and process order, and how can we look/check/verify that without using a session we retrieve in the correct order, explain with an example of C # and . .NET.
Let me make it clearer,
I uploaded 1000 messages to Azure Service Bus.
I applied a ServiceBusTrigger onto an Azure Functions, And printing the message body then, the function is triggered 1000 times, as many messages are present on the service bu, but the catch is the retrieval order is random, not uniform as I uploaded, but this document says to maintain retrieval order, we don't need to use sessions.
How can we verify the retrieval order without using sessions
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Answer 1

Hello Abhay Pratap Singh,

Azure Service Bus guarantees FIFO (first-in-first-out) only within sessions. If you do not use sessions, strict global FIFO is not guaranteed, because messages may be delivered concurrently to multiple function instances or across partitions.

However, there are some approaches to approximate FIFO without sessions:

Configure your queue for only one processing instance by limiting concurrency.
In Azure Functions, this means setting maxConcurrentCalls (Service Bus SDK) or host.json concurrency settings to 1. host.json Example for Single-Consumer: { "version": "2.0", "extensions": { "serviceBus": { "maxConcurrentCalls": 1 } } } Enabling the First-In-First-Out pattern in Microsoft Azure Service Bus Queues and Topics For true FIFO, using sessions is the recommended approach in Service Bus.

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Azure Service Bus Topics Sequence vs Sessions

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