Event Hubs Receiver Epoch
Event Hubs CreateReceiverAsync API has several overloads of which a few of them take a parameter named "epoch". This blog is to explain the details of this epoch parameter.
CreateReceiverAsync(String) | Asynchronous version of CreateReceiver(String). | |
CreateReceiverAsync(String, DateTime) | Asynchronous version of CreateReceiver(String, DateTime). | |
CreateReceiverAsync(String, Int64) | Asynchronous version of CreateReceiver(String, Int64). | |
CreateReceiverAsync(String, String) | Asynchronous version of CreateReceiver(String, String). | |
CreateReceiverAsync(String, DateTime, Int64) | Asynchronous version of CreateReceiver(String, DateTime, Int64). | |
CreateReceiverAsync(String, String, Int64) | Asynchronous version of CreateReceiver(String, String, Int64). |
Here is how the receive epoch works:
With Epoch: Receiver epoch feature provides users ability to ensure that there is only one receiver on a consumer group at any point in time, with the following rules.
a) If there is no existing receiver on a consumer group then user can create a receiver with any epoch value.
b) If there is a receiver with epoch value e1 and a new receiver is created with an epoch value e2 where e1 <= e2 then receiver with e1 will be disconnected automatically, receiver with e2 get created successfully.
c) If there is a receiver with epoch value e1 and a new receiver is created with an epoch value e2 where e1 > e2 then creation of e2 with fail with the error “A receiver with epoch e1 already exists”
No Epoch: There are some scenarios in stream processing where users would like to create multiple receivers on a single consumer group. To support such scenarios we do have ability to CreateReceiver without epoch and in this case we allow upto 5 concurrent receivers on the consumer group.
Mixed Mode: We usually don’t recommend application usage where you create a receiver with epoch and then switch to no-epoch or vice-versa on the same consumer group. Although this can happen during application testing, we handle the situation like this:
a) If there is a receiver already created with epoch e1 and is actively receiving events and a new receiver is created with no epoch , then the creation of new receiver will fail. Epoch receivers always take precedence in the system.
b) If there was a receiver already created with epoch e1 and got is disconnected and a new receiver is created with no epoch on a new MessagingFactory, then the creation of new receiver will succeed. There is a caveat here that our system will detect the “receiver disconnection” after ~10 minutes.
c) If there are one or more receivers created with no epoch and a new receiver is created with epoch e1 then all the old receivers get disconnected.
- Anonymous
January 15, 2015
Any clue, what is the purpose of this 'epoch'? It seems very confusing.