adds notes, ensures that we optimize property data when using msgpack binary serialization too!

src/Umbraco.Web/PublishedCache/NuCache/DataSource/Lz4DictionaryOfPropertyDataSerializer.cs

@@ -67,7 +67,8 @@ namespace Umbraco.Web.PublishedCache.NuCache.DataSource
                     pdata.Value = ReadObject(stream);
 
                     switch (map.CompressLevel)
-                    {                        
+                    {
+                        // If the property is compressed at either the DB or Nucache level, it means it's compressed here and we need to decompress
                         case NucachePropertyCompressionLevel.SQLDatabase:
                         case NucachePropertyCompressionLevel.NuCacheDatabase:
                             if (!(pdata.Value is null) && pdata.Value is byte[] byteArrayValue)
@@ -80,8 +81,7 @@ namespace Umbraco.Web.PublishedCache.NuCache.DataSource
                                         break;
                                     case NucachePropertyDecompressionLevel.NotCompressed:
                                         //Shouldn't be any not compressed
-                                        // TODO: Do we need to throw here?
-                                        break; 
+                                        throw new InvalidOperationException($"{NucachePropertyDecompressionLevel.NotCompressed} cannot be a decompression option for property {alias} since it's compresion option is {map.CompressLevel}");
                                     case NucachePropertyDecompressionLevel.Immediate:
                                     default:
                                         pdata.Value = Encoding.UTF8.GetString(LZ4Pickler.Unpickle(byteArrayValue));

src/Umbraco.Web/PublishedCache/NuCache/DataSource/MsgPackContentNestedDataSerializer.cs

@@ -97,7 +97,12 @@ namespace Umbraco.Web.PublishedCache.NuCache.DataSource
 
         public ContentNestedData DeserializeBytes(byte[] data) => MessagePackSerializer.Deserialize<ContentNestedData>(data, _options);
 
-        public byte[] SerializeBytes(ContentNestedData nestedData) => MessagePackSerializer.Serialize(nestedData, _options);
+        public byte[] SerializeBytes(ContentNestedData nestedData)
+        {
+            Optimize(nestedData);
+
+            return MessagePackSerializer.Serialize(nestedData, _options);
+        }
 
         //private class ContentNestedDataResolver : IFormatterResolver
         //{

src/Umbraco.Web/PublishedCache/NuCache/DataSource/SerializerBase.cs

@@ -16,6 +16,10 @@ namespace Umbraco.Web.PublishedCache.NuCache.DataSource
         private const char PrefixDouble = 'B';
         private const char PrefixDateTime = 'D';
         private const char PrefixByte = 'O';
+
+        // TODO: It might make sense to have another prefix for an LZ4 compressed byte array.
+        // Would be an improvement for the SQLDatabase compression option because then you could mix compressed and decompressed properties with the same alias.
+        // For example, don't compress recent content, but compress older content.
         private const char PrefixByteArray = 'A';
 
         protected string ReadString(Stream stream) => PrimitiveSerializer.String.ReadFrom(stream);