reduce message sizes for Gossip and DeltaPropagation in ddata, #27175 (#27176)

akka-distributed-data/src/main/resources/reference.conf

@@ -24,7 +24,7 @@ akka.cluster.distributed-data {
 
   # Maximum number of entries to transfer in one gossip message when synchronizing
   # the replicas. Next chunk will be transferred in next round of gossip.
-  max-delta-elements = 1000
+  max-delta-elements = 500
   
   # The id of the dispatcher to use for Replicator actors.
   # If specified you need to define the settings of the actual dispatcher.
@@ -65,7 +65,7 @@ akka.cluster.distributed-data {
     # Some complex deltas grow in size for each update and above this
     # threshold such deltas are discarded and sent as full state instead.
     # This is number of elements or similar size hint, not size in bytes.
-    max-delta-size = 200
+    max-delta-size = 50
   }
   
   durable {

akka-docs/src/main/paradox/project/migration-guide-2.5.x-2.6.x.md

@@ -354,6 +354,19 @@ akka.cluster.sharding.passivate-idle-entity-after = off
 
 It is always disabled if @ref:[Remembering Entities](../cluster-sharding.md#remembering-entities) is enabled.
 
+### Distributed Data
+
+Configuration properties for controlling sizes of `Gossip` and `DeltaPropagation` messages in Distributed Data
+have been reduced. Previous defaults sometimes resulted in messages exceeding max payload size for remote
+actor messages.
+
+The new configuration properties are:
+
+```
+akka.cluster.distributed-data.max-delta-elements = 500
+akka.cluster.distributed-data.delta-crdt.max-delta-size = 50
+```
+
 ### CoordinatedShutdown is run from ActorSystem.terminate
 
 No migration is needed but it is mentioned here because it is a change in behavior.