I am working in azure event hub. I have some doubts.
What is Partition Id in Azure event hub receiver? Is this Id is same as partition Key in Azure event hub Publisher?
What is Offset? ,What the use of it in azure event hub consumer?
Can I consume the message with out using consumer group?
Can I consume the message with single receiver?
What is the use of blob in event hub consumer? I want only view the message what ever I sent.
This article Event Hubs Overview should answer your questions in detail, but to summarize:
When you create a new Event Hub in the portal, you specify how many partitions you need. The Publisher hashes the partition key of an event to determine which partition to send the event to. An event hub receiver receives events from those partitions.
An event hub consumer tracks which events it has received by by using an offset into each partition. By changing the offset you can, for example, re-read events from a partition.
You must have at least one consumer group (there is a default one). Each consumer group has it's own view of the partitions (different offset values) that let it read the events from the partitions independently of the other consumer groups.
Typically, you have one receiver per partition to enable scale out. An event hub has between 8 and 16 partitions.
Offset values are managed by the client. You can checkpoint your latest position in each partition to enable you to restart at the latest event if the client restarts. The checkpoint mechanism writes the latest offset values to blob storage.
Related
I'm new to Azure Event Hubs and I'm having a hard time understanding the Partitions.
I have the following scenario:
1 Event Hub Namespace
1 actual Event Hub
2 Partitions in the Event Hub
2 Consumer groups
1 Event Producer
2 Event Consumers, one per Consumer group
The Event Producer sends out 10 events to the Event hub. The events gets distributed to the partitions with a round-robin mechanism. So the Event hub looks like this:
Partition 1: [0] [2] [5] [6] [8]
Partition 2: [1] [3] [4] [7] [9]
When the Event Consumers start reading, each consumer would end up with only a part of the events, like so:
Consumer 1: Gets events 0,2,5,6,8
Consumer 2: Gets events 1,3,4,7,9
Is it true that a Consumer group can only access a subset of the Partitions?
My assumption is that the Event Hub architecture supports broadcasting of events to multiple consumers. And that every consumer wants all the events.
But it seems to me that Event Hub isn't designed to have all consumers get all the events, but I don't understand why that would be useful.
Can anyone help me understand Partitions?
Each Event Hubs partition is a persistent stream of events that is available to all consumers, regardless of which consumer group they are associated with. Any consumer can read from any partition at any point in the event stream.
Partitions are used to help scale resources to support a greater degree of concurrency and increase throughput for the Event Hub. Generally speaking, the more partitions that are in use, the more concurrent operations the Event Hub can handle. More information can be found in the Event Hubs overview.
My assumption is that the Event Hub architecture supports broadcasting of events to multiple consumers.
Not quite; consumers are responsible for pulling events from the partitions of an Event Hub, they are not pushed to consumers. Any consumer with permissions can connect to a partition and read independently. Events are not removed once read, they exist in the partition until their age exceeds the retention period.
But it seems to me that Event Hub isn't designed to have all consumers get all the events
That is not correct. Event Hubs exposes the events for any consumer wishing to read them. Using a client like the EventProcessorClient from the Event Hubs SDK allows an application to consume from all partitions without having to manage each partition consumer individually.
I have a data pipeline set up in Azure where I send messages to an IoTHub which then routes those messages to an EventHub. When I read from the EventHub using the standard EventProcessorHost method, I find that only one of the partitions is being read from. I assume that only one partition is actually having messages routed to it. I have not specified a partition key anywhere and expect that the messages would be routed to all of the partitions of the event hub using round robin (as per the documentation at https://learn.microsoft.com/en-us/azure/event-hubs/event-hubs-programming-guide).
How can I configure my setup to route messages to all partitions of the event hub?
Like I said in the comment:
Is it possible you are only receiving data from one device? IoT Hub does automatic partitioning based on the deviceId, so the partition affinity might be the cause.
I have an Azure Function that listens for messages in an Event Hub. The function takes messages from the Event Hub, processes them, and passes them to another Hub. At this point the messages are removed from the Event Hub.
If the Function fails processing the message for whatever reason, is it possible to tell the Event Hub to not remove the message, and to try to deliver it to the Function again at some point in the future?
I understand that the Event Hubs have a maximum retention period of 7 days. I would like for the Event Hub & Function to continue trying during that period.
Readers never "remove" messages from an Event Hub. They are different from Service Bus Topics and Queues in this.
Event Hubs rely on clients to maintain their own bookmarks for each partition. The high-level API EventProcessorHost does this for you:
The EventProcessorHost class also implements an Azure storage-based
checkpointing mechanism. This mechanism stores the offset on a per
partition basis, so that each consumer can determine what the last
checkpoint from the previous consumer was.
But the lower-level EventHubReceiver exposes the StartingSequenceNumber property for you to control this explicitly.
However a desire for guaranteed delivery strongly suggests that you may want to copy the messages requiring guaranteed delivery from an Event Hub to a Service Bus Topic or Queue or perhaps an Azure SQL Database table for processing.
For event hub if we face a fault and the consumer crashes, then next time when it comes up how does it get to query what checkpoint it was on for the partition it gets hold of from the storage so that it can compare the reference sequence id of that message and incoming messages and process only the ones that come after that sequence id?
To save the checkpoint there is an API, but how to retrieve it?
As you know that Event Hub Check pointing is purely client side,i.e., you can store the current offset in the storage account linked with your event hub using the method
await context.CheckpointAsync();
in your client code. This will be converted to a storage account call. This is not related to any EventHub Service call.
Whenever there is a failure in your Event hub, you can read the latest(updated) offset from the storage account to avoid duplication of events.This must be handled by you on your client side code and it will not be handled by the event hub on its own.
If a reader disconnects from a partition, when it reconnects it begins reading at the checkpoint that was previously submitted by the last reader of that partition in that consumer group. When the reader connects, it passes the offset to the event hub to specify the location at which to start reading. In this way, you can use checkpointing to both mark events as "complete" by downstream applications, and to provide resiliency if a failover between readers running on different machines occurs. It is possible to return to older data by specifying a lower offset from this checkpointing process. Through this mechanism, checkpointing enables both failover resiliency and event stream replay.
Moreover, failure in an event hub is rare and duplicate events are less frequent. For more details on building a work flow with no duplicate events refer this stack overflow answer
The details of the checkpoint will be saved in the storage account linked to event hub in the format give below. This can be read using WindowsAzure.Storage client to do custom validation of sequence number of the last event received.
When creating a new Azure IOT Hub you are asked how many device-to-cloud partitions you need. You can select between 2-32 partitions for standard tiers.
I understand that the SKU and number of units determine the maximum daily quota of messages that you can send to IOT Hub. And that it is recommended to shard your devices into multiple IOT hubs to smooth traffic bursts. However, device-to-cloud partitions need clarification.
1>> What is the purpose of those device-to-cloud partitions under a single IOT hub?
2>> How are we supposed to take advantage of those IOT Hub device-to-cloud partitions?
Thanks.
1>> What is the purpose of those device-to-cloud partitions under a
single IOT hub?
Partition property is setting for Event Hub-compatible messaging endpoint(messages/events) built in Azure IoT Hub. From here we can see "partitions" is a concept belongs to Event Hub.
Event Hubs is designed to allow a single partition reader per consumer group. A single partition within a consumer group cannot have more than 5 concurrent readers connected at any time. More partitions enables you to have more concurrent readers processing your data, improving your aggregate throughput.
Ref: Built-in endpoint: messages/events and How many partitions do I need?
2>> How are we supposed to take advantage of those IOT Hub
device-to-cloud partitions?
Event Hubs has two primary models for event consumption: direct receivers and higher-level abstractions, such as EventProcessorHost. Direct receivers are responsible for their own coordination of access to partitions within a consumer group.
Ref:Event consumers.
More information about the partitioning model of Azure Event Hubs are here.