From 0d6325a8f25027fbf8819517d575d3ae3401e842 Mon Sep 17 00:00:00 2001
From: Aaron Stannard <aaron@petabridge.com>
Date: Tue, 31 May 2022 14:54:50 -0500
Subject: [PATCH] de-duplicate only identical `ShardHomeAllocated` messages

close https://github.com/akkadotnet/akka.net/issues/5604
---
 .../PersistentShardCoordinator.cs                | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/contrib/cluster/Akka.Cluster.Sharding/PersistentShardCoordinator.cs b/src/contrib/cluster/Akka.Cluster.Sharding/PersistentShardCoordinator.cs
index 645e0a6c360..ff567449a40 100644
--- a/src/contrib/cluster/Akka.Cluster.Sharding/PersistentShardCoordinator.cs
+++ b/src/contrib/cluster/Akka.Cluster.Sharding/PersistentShardCoordinator.cs
@@ -109,11 +109,11 @@ public IImmutableSet<ShardId> AllShards
             }
 
             /// <summary>
-            /// TBD
+            /// Feed an event into the ShardCoordinator state.
             /// </summary>
-            /// <param name="e">TBD</param>
-            /// <exception cref="ArgumentException">TBD</exception>
-            /// <returns>TBD</returns>
+            /// <param name="e">The event to process.</param>
+            /// <exception cref="ArgumentException">Thrown if an event is illegal in the current state.</exception>
+            /// <returns>An update copy of this state.</returns>
             public State Updated(IDomainEvent e)
             {
                 switch (e)
@@ -1361,8 +1361,12 @@ protected override bool ReceiveRecover(object message)
                             if (CurrentState.RegionProxies.Contains(proxyTerminated.RegionProxy))
                                 CurrentState = CurrentState.Updated(evt);
                             return true;
-                        case ShardHomeAllocated _:
-                            CurrentState = CurrentState.Updated(evt);
+                        case ShardHomeAllocated homeAllocated:
+                            // if we already have identical ShardHomeAllocated data, skip processing it
+                            // addresses https://github.com/akkadotnet/akka.net/issues/5604
+                            if(!(CurrentState.Shards.TryGetValue(homeAllocated.Shard, out var currentShardRegion) 
+                               && Equals(homeAllocated.Region, currentShardRegion)))
+                                CurrentState = CurrentState.Updated(evt);
                             return true;
                         case ShardHomeDeallocated _:
                             CurrentState = CurrentState.Updated(evt);