Avoid repeated reloads of content and media cache following Deploy operations.

src/Umbraco.Tests/Cache/DistributedCacheBinderTests.cs

@@ -9,6 +9,7 @@
 using Umbraco.Core.Models;
 using Umbraco.Core.Models.Membership;
 using Umbraco.Core.Services;
+using Umbraco.Core.Services.Changes;
 using Umbraco.Tests.Testing;
 using Umbraco.Tests.Testing.Objects.Accessors;
 using Umbraco.Web;
@@ -148,7 +149,6 @@ public void CanHandleEvent()
             {
                 // works because that event definition maps to an empty handler
                 new EventDefinition<IContentTypeService, SaveEventArgs<IContentType>>(null, Current.Services.ContentTypeService, new SaveEventArgs<IContentType>(Enumerable.Empty<IContentType>()), "Saved"),
-
             };
 
             var umbracoContextFactory = new UmbracoContextFactory(
@@ -166,5 +166,19 @@ public void CanHandleEvent()
             var refreshers = new DistributedCacheBinder(null, umbracoContextFactory, null);
             refreshers.HandleEvents(definitions);
         }
+
+        [Test]
+        public void OnlyHandlesOnContentTypeEvent()
+        {
+            var definitions = new IEventDefinition[]
+            {
+                new EventDefinition<IContentTypeService, ContentTypeChange<IContentType>.EventArgs>(null, Current.Services.ContentTypeService, new ContentTypeChange<IContentType>.EventArgs(Enumerable.Empty<ContentTypeChange<IContentType>>()), "Changed"),
+                new EventDefinition<IContentTypeService, SaveEventArgs<IContentType>>(null, Current.Services.ContentTypeService, new SaveEventArgs<IContentType>(Enumerable.Empty<IContentType>()), "Saved"),
+                new EventDefinition<IContentTypeService, ContentTypeChange<IContentType>.EventArgs>(null, Current.Services.ContentTypeService, new ContentTypeChange<IContentType>.EventArgs(Enumerable.Empty<ContentTypeChange<IContentType>>()), "Changed"),
+                new EventDefinition<IContentTypeService, SaveEventArgs<IContentType>>(null, Current.Services.ContentTypeService, new SaveEventArgs<IContentType>(Enumerable.Empty<IContentType>()), "Saved"),
+            };
+            var result = DistributedCacheBinder.GetReducedEventList(definitions);
+            Assert.AreEqual(1, result.Count());
+        }
     }
 }

src/Umbraco.Web/Cache/DistributedCacheBinder.cs

@@ -61,11 +61,15 @@ internal static MethodInfo FindHandler(IEventDefinition eventDefinition)
         /// <inheritdoc />
         public void HandleEvents(IEnumerable<IEventDefinition> events)
         {
-            // ensure we run with an UmbracoContext, because this may run in a background task,
-            // yet developers may be using the 'current' UmbracoContext in the event handlers
+            // Ensure we run with an UmbracoContext, because this may run in a background task,
+            // yet developers may be using the 'current' UmbracoContext in the event handlers.
             using (_umbracoContextFactory.EnsureUmbracoContext())
             {
-                foreach (var e in events)
+                // When it comes to content types types, a change to any single one will trigger a reload of the content and media caches.
+                // As far as I (AB) can tell, there's no type specific logic here, they all clear caches for all content types, and trigger a reload of all content and media.
+                // We also have events registered for Changed and Saved, which do the same thing, so really only need one of these.
+                // Hence if we have more than one document or media types, we can and should only handle one of the events for one, to avoid repeated cache reloads.
+                foreach (var e in GetReducedEventList(events))
                 {
                     var handler = FindHandler(e);
                     if (handler == null)
@@ -80,5 +84,49 @@ public void HandleEvents(IEnumerable<IEventDefinition> events)
                 }
             }
         }
+
+        // Internal for tests
+        internal static IEnumerable<IEventDefinition> GetReducedEventList(IEnumerable<IEventDefinition> events)
+        {
+            var reducedEvents = new List<IEventDefinition>();
+
+            var gotDoumentType = false;
+            var gotMediaType = false;
+            var gotMemberType = false;
+
+            foreach (var evt in events)
+            {
+                if (evt.Sender.ToString().Contains(nameof(Core.Services.Implement.ContentTypeService)))
+                {
+                    if (gotDoumentType == false)
+                    {
+                        reducedEvents.Add(evt);
+                        gotDoumentType = true;
+                    }
+                }
+                else if (evt.Sender.ToString().Contains(nameof(Core.Services.Implement.MediaTypeService)))
+                {
+                    if (gotMediaType == false)
+                    {
+                        reducedEvents.Add(evt);
+                        gotMediaType = true;
+                    }
+                }
+                else if (evt.Sender.ToString().Contains(nameof(Core.Services.Implement.MemberTypeService)))
+                {
+                    if (gotMemberType == false)
+                    {
+                        reducedEvents.Add(evt);
+                        gotMemberType = true;
+                    }
+                }
+                else
+                {
+                    reducedEvents.Add(evt);
+                }
+            }
+
+            return reducedEvents;
+        }
     }
 }