Projection propagation notification

[akka]

Projection propagation notification

[longmuir]

This sounds really useful - and would help address the usual concerns that people have around eventual consistency (in addition to some form of Telemetry metrics for an aggregated view of propagation time).

[ignasi35]

This is a use case that's specific for projections over akka persistence journals. Should we include it as part of akka-projections?

(off-topic, brain dump) It'll require changing the akka persistence api and plugins (in either the two alternatives @chbatey suggests). (/off-topic, brain dump)

Maybe, a solution would be to guide the user into registering a StatusObserver and implement the progress method so they're notified of each envelope that's been successfully processed by the projection.