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Make ShardingDirectReplication private (#29492)

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* Make ShardingDirectReplication private

And provider user API to provide ReplicaId so that local messages don't
need to be forwarded to sharding to just be dropped

* Update docs to say direct replication is on my default

* Doh
This commit is contained in:
Christopher Batey 2020-08-14 15:02:38 +01:00
parent 260276fd90
commit eae102acb1
5 changed files with 32 additions and 52 deletions
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13
akka-docs/src/main/paradox/typed/replicated-eventsourcing.md
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@ -384,18 +384,15 @@ with a single stream of tagged events from all replicas without duplicates.
## Direct Replication of Events
Normally an event has to be written in the journal and then picked up by the trailing read journal in the other replicas.
As an optimization the replicated events can be published across the Akka cluster to the replicas. The read side
query is still needed as delivery is not guaranteed, but can be configured to poll the database less often since most
In addition to reading each replica's events from the database the replicated events are published across the Akka cluster to the replicas when used with Cluster Sharding.
The query is still needed as delivery is not guaranteed, but can be configured to poll the database less often since most
events will arrive at the replicas through the cluster.
To enable this feature you first need to enable event publishing on the @scala[`EventSourcedBehavior`]@java[`ReplicatedEventSourcedBehavior`] with `withEventPublishing`
and then enable direct replication through `withDirectReplication(true)` on @apidoc[ReplicatedEntityProvider] (if not using
replicated sharding the replication can be run standalone by starting the @apidoc[ShardingDirectReplication] actor).
This feature is enabled by default when using sharding.
To disable this feature you first need to disable event publishing on the @scala[`EventSourcedBehavior`]@java[`ReplicatedEventSourcedBehavior`] with `withEventPublishing`
and then disable direct replication through `withDirectReplication(true)` on @apidoc[ReplicatedEntityProvider]
The "event publishing" feature publishes each event to the local system event bus as a side effect after it has been written,
the @apidoc[ShardingDirectReplication] actor subscribes to these events and forwards them to the replicas allowing them
to fast forward the stream of events for the origin replica. (With additional potential future support in journals for fast forwarding [#29311](https://github.com/akka/akka/issues/29311)).
## Hot Standby