Can anybody tell me how to use dead event store?
I have create a channel A with dead event store channel B. When i publish a document which can’t be subscribed with any trigger, I found the um don’t moved the event to channel B. It’s not like dead letter queue in broker.

The dead letter queue behaviour is slight different in UM as compared to Broker, as per the wiki, Dead letter queue - In message queueing the dead letter queue is a service implementation to store messages that meet one or more of the following criteria :

Message that is sent to a queue that does not exist.
Queue length limit exceeded.
Message length limit exceeded.
Message is rejected by another queue exchange.
Message reaches a threshold read counter number, because it is not consumed. Sometimes this is called a “back out queue”.

As per the above information you can set a TTL or Capacity Params on Channel/Topic with Honour Capacity=true by default. If the messages are not consumed by the subscriber within the TTL the messages will then go to DES channel which can be subscribed by the trigger and process these messages.

However, as per the dead letter queue does not work in UM if there is no intended active subscriber on a channel or topic with TTL=0 and Capacity=0, it still stays in the main channel/topic and do not move to DES channel.

Product team can provide more information on this. But there are some fixes and enhancements done in UM 10.0 release. Please check the documentation for more details.