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Merge pull request #18436 from akka/wip-sharding-migration-guide-patriknw

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=doc Clarify sharding data compatibility
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Patrik Nordwall 2015-09-16 12:52:56 +02:00
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akka-docs/rst/project/migration-guide-2.3.x-2.4.x.rst
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@ -295,6 +295,26 @@ actor external actor of how to allocate shards or rebalance shards.
For the synchronous case you can return the result via ``scala.concurrent.Future.successful`` in Scala or
``akka.dispatch.Futures.successful`` in Java.
Cluster Sharding internal data
==============================
The Cluster Sharding coordinator stores the locations of the shards using Akka Persistence.
This data can safely be removed when restarting the whole Akka Cluster.
The serialization format of the internal persistent events stored by the Cluster Sharding coordinator
has been changed and it cannot load old data from 2.3.x or some 2.4 milestone.
The ``persistenceId`` of the Cluster Sharding coordinator has been changed since 2.3.x so
it should not load such old data, but it can be a problem if you have used a 2.4
milestone release. In that case you should remove the persistent data that the
Cluster Sharding coordinator stored. Note that this is not application data.
Consult the Journal Plugin and Snapshot Store Plugin documentation or backend
data store documentation for information about how to remove such data.
The new ``persistenceId`` is ``s"/sharding/${typeName}Coordinator"``.
The old ``persistenceId`` is ``s"/user/sharding/${typeName}Coordinator/singleton/coordinator"``.
ClusterSingletonManager and ClusterSingletonProxy construction
==============================================================