哪些代理为崩溃的客户端支持对子发布丢失消息的内置恢复？

Question

In an event-sourcing scenario, a crashed event-consumer client should got all missed events-messages published by the source while it was down.

The recovery algorithm (assuming it is right) would be:

1. subscribe to the event source (connection 1)

2. request the server (connection 2) all the missed messages ("missed-pack") since a given timestamp (just before the crash); and apply missed events locally

3. start reading messages from the subscription connection, applying those with timestamp greater than the last one applied from the missed-pack. (Here, we are assuming that all messages published between the subscription and the first read, will be delivered to the client. Maybe, some of the first messages read would be the last ones in the missed-pack, hence the caution).

What brokers (message brokers, no-sql databases, ...) do support programming this recovery process "out of out the box", ie not having to program at the server (event source) side.

Thanks.

Answer 1

Maybe what you are looking for is for a "catch up subscription" capability. It is fully suported by Get Event Store . But this is actually a database, but has excelent topic based pub/sub features, with an http API also.

What you might not know yet is that you can do that by yourself, just make a consumer driven subscription, where the consumer knows the last checkpoint (never a timestamp, which can led to nasty concurrency problems) that where successfuly processed, not the producer. So the client can always resume where it left.

Hope this helps