perf(subscriptions): hot-path quick wins and bug fixes

src/Azure/src/Eventuous.Azure.ServiceBus/Subscriptions/ServiceBusSubscription.cs

@@ -110,7 +110,6 @@ CancellationToken                     ct
 
         Logger.Current = Log;
         var evt                   = DeserializeData(contentType, eventType, msg.Body, streamName);
-        var applicationProperties = msg.ApplicationProperties.Concat(MessageProperties(msg));
 
         var ctx = new MessageConsumeContext(
             msg.MessageId,
@@ -123,7 +122,7 @@ CancellationToken                     ct
             run.NextSequence(),
             msg.EnqueuedTime.UtcDateTime,
             evt,
-            AsMeta(applicationProperties),
+            evt is null ? null : AsMeta(msg.ApplicationProperties.Concat(MessageProperties(msg))),
             SubscriptionId,
             ct
         );

src/Core/src/Eventuous.Application/AggregateService/CommandHandlerBuilder.cs

@@ -245,9 +245,9 @@ RegisteredHandler<TAggregate, TState, TId> Build() {
         );
 
         Func<TCommand, IEventWriter> DefaultResolveWriter()
-            => _ => Ensure.NotNull(writer, $"Function to resolve event writer from {typeof(TCommand).Name} is not defined and no default writer is set");
+            => _ => writer ?? throw new ArgumentNullException($"Function to resolve event writer from {typeof(TCommand).Name} is not defined and no default writer is set");
 
         Func<TCommand, IEventReader> DefaultResolveReader()
-            => _ => Ensure.NotNull(reader, $"Function to resolve event reader from {typeof(TCommand).Name} is not defined and no default reader is set");
+            => _ => reader ?? throw new ArgumentNullException($"Function to resolve event reader from {typeof(TCommand).Name} is not defined and no default reader is set");
     }
 }

src/Core/src/Eventuous.Application/Diagnostics/ApplicationEventSource.cs

@@ -18,10 +18,14 @@ class ApplicationEventSource : EventSource {
     const int CommandHandlerRegisteredId        = 5;
 
     [NonEvent]
-    public void CommandHandlerNotFound<TCommand>() => CommandHandlerNotFound(typeof(TCommand).Name);
+    public void CommandHandlerNotFound<TCommand>() {
+        if (IsEnabled(EventLevel.Error, EventKeywords.All)) CommandHandlerNotFound(typeof(TCommand).Name);
+    }
 
     [NonEvent]
-    public void ErrorHandlingCommand<TCommand>(Exception e) => ErrorHandlingCommand(typeof(TCommand).Name, e.ToString());
+    public void ErrorHandlingCommand<TCommand>(Exception e) {
+        if (IsEnabled(EventLevel.Error, EventKeywords.All)) ErrorHandlingCommand(typeof(TCommand).Name, e.ToString());
+    }
 
     [NonEvent]
     public void CommandHandled<TCommand>() {

src/Core/src/Eventuous.Application/Diagnostics/CommandServiceActivity.cs

@@ -9,27 +9,33 @@ namespace Eventuous.Diagnostics;
 using Tracing;
 
 static class CommandServiceActivity {
+    // Shared by every traced service, whatever its state type: the metrics listener only observes the latest
+    // listener announced under a name, so a listener per service would hide the metrics of all but one.
+    static readonly DiagnosticSource MetricsSource = new DiagnosticListener(CommandServiceMetrics.ListenerName);
+
     public static async Task<Result<T>> TryExecute<T, TCommand>(
             string                     appServiceTypeName,
             TCommand                   command,
-            DiagnosticSource           diagnosticSource,
             HandleCommand<T, TCommand> handleCommand,
             CancellationToken          cancellationToken
         ) where TCommand : class where T : State<T>, new() {
         var cmdName = command.GetType().Name;
 
         using var activity = StartActivity(appServiceTypeName, cmdName);
-        using var measure  = Measure.Start(diagnosticSource, new CommandServiceMetricsContext(appServiceTypeName, cmdName));
+        // Nobody listening means nothing to record, so skip the measure and its context rather than allocate both.
+        using var measure = MetricsSource.IsEnabled(Measure.EventName)
+            ? Measure.Start(MetricsSource, new CommandServiceMetricsContext(appServiceTypeName, cmdName))
+            : null;
 
         try {
             var result = await handleCommand(command, cancellationToken).NoContext();
             activity?.SetActivityStatus(result is { Success: true } ? ActivityStatus.Ok() : ActivityStatus.Error(result.Exception));
-            if (!result.Success) measure.SetError();
+            if (!result.Success) measure?.SetError();
 
             return result;
         } catch (Exception e) {
             activity?.SetActivityStatus(ActivityStatus.Error(e));
-            measure.SetError();
+            measure?.SetError();
 
             throw;
         }

src/Core/src/Eventuous.Application/Diagnostics/TracedCommandService.cs

@@ -1,17 +1,14 @@
 // Copyright (C) Eventuous HQ OÜ. All rights reserved
 // Licensed under the Apache License, Version 2.0.
 
-using System.Diagnostics;
-
 namespace Eventuous.Diagnostics;
 
 public class TracedCommandService<TState> : ICommandService<TState> where TState : State<TState>, new() {
     public static ICommandService<TState> Trace(ICommandService<TState> appService) => new TracedCommandService<TState>(appService);
 
     ICommandService<TState> InnerService { get; }
 
-    readonly string           _appServiceTypeName;
-    readonly DiagnosticSource _metricsSource = new DiagnosticListener(CommandServiceMetrics.ListenerName);
+    readonly string _appServiceTypeName;
 
     TracedCommandService(ICommandService<TState> appService) {
         _appServiceTypeName = appService.GetType().Name;
@@ -23,7 +20,6 @@ public Task<Result<TState>> Handle<TCommand>(TCommand command, CancellationToken
         => CommandServiceActivity.TryExecute(
             _appServiceTypeName,
             command,
-            _metricsSource,
             InnerService.Handle,
             cancellationToken
         );

src/Core/src/Eventuous.Application/ThrowingCommandService.cs

@@ -15,6 +15,6 @@ public async Task<Result<TState>> Handle<TCommand>(TCommand command, Cancellatio
 
         result.ThrowIfError();
 
-        throw new ApplicationException($"Error handling command {command}");
+        return result;
     }
 }

src/Core/src/Eventuous.Diagnostics/ActivityExtensions.cs

@@ -5,9 +5,10 @@ namespace Eventuous.Diagnostics;
 
 public static class ActivityExtensions {
     extension(Activity activity) {
+        // Same result as searching Tags, which only yields string values, without allocating an enumerator and a closure.
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         string? GetParentTag(string tag)
-            => activity.Parent?.Tags.FirstOrDefault(x => x.Key == tag).Value;
+            => activity.Parent?.GetTagItem(tag) as string;
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public Activity CopyParentTag(string tag, string? parentTag = null) {

src/Core/src/Eventuous.Diagnostics/ActivityStatus.cs

@@ -4,8 +4,11 @@
 namespace Eventuous.Diagnostics;
 
 public record ActivityStatus(ActivityStatusCode StatusCode, string? Description, Exception? Exception) {
+    static readonly ActivityStatus PlainOk = new(ActivityStatusCode.Ok, null, null);
+
+    // Shared when there's no description: the record is immutable, and this is the status of every successful span.
     public static ActivityStatus Ok(string? description = null)
-        => new(ActivityStatusCode.Ok, description, null);
+        => description == null ? PlainOk : new(ActivityStatusCode.Ok, description, null);
 
     public static ActivityStatus Error(Exception? exception = null, string? description = null)
         => new(ActivityStatusCode.Error, description ?? exception?.Message, exception);

src/Core/src/Eventuous.Diagnostics/Metrics/Measure.cs

@@ -16,12 +16,11 @@ public sealed class Measure(DiagnosticSource diagnosticSource, object context) :
         Justification = "MeasureContext is not referencing anything."
     )]
     void Record() {
-        var stoppedAt = DateTime.UtcNow;
-        var duration  = stoppedAt - _startedAt;
+        var duration = Stopwatch.GetElapsedTime(_startedAt);
         diagnosticSource.Write(EventName, new MeasureContext(duration, _error, context));
     }
 
-    readonly DateTime _startedAt = DateTime.UtcNow;
+    readonly long _startedAt = Stopwatch.GetTimestamp();
 
     bool _error;
 

src/Core/src/Eventuous.Domain/Aggregate.cs

@@ -13,7 +13,7 @@ namespace Eventuous;
     /// <summary>
     /// Get the list of pending changes (new events) within the scope of the current operation.
     /// </summary>
-    public IReadOnlyCollection<object> Changes => _changes.AsReadOnly();
+    public IReadOnlyCollection<object> Changes => _changesView ??= _changes.AsReadOnly();
 
     /// <summary>
     /// A collection with all the aggregate events, previously persisted and new
@@ -36,10 +36,13 @@ namespace Eventuous;
     /// The current version is set to the original version when the aggregate is loaded from the store.
     /// It should increase for each state transition performed within the scope of the current operation.
     /// </summary>
-    public long CurrentVersion => OriginalVersion + Changes.Count;
+    public long CurrentVersion => OriginalVersion + _changes.Count;
 
     readonly List<object> _changes = [];
 
+    // The view wraps the live list, so it can be created once and reused
+    IReadOnlyCollection<object>? _changesView;
+
     /// <summary>
     /// Adds an event to the list of pending changes.
     /// </summary>

src/Core/src/Eventuous.Persistence/Diagnostics/Tracing/BaseTracer.cs

@@ -18,7 +18,7 @@ public abstract class BaseTracer {
 
     protected async Task<T> Trace<T>(StreamName stream, string operation, Func<Task<T>> task) {
         using var activity = StartActivity(stream, operation);
-        using var measure  = Measure.Start(MetricsSource, new PersistenceMetricsContext(ComponentName, operation));
+        using var measure  = StartMeasure(operation);
 
         try {
             var result = await task().NoContext();
@@ -27,22 +27,22 @@ protected async Task<T> Trace<T>(StreamName stream, string operation, Func<Task<
             return result;
         } catch (Exception e) {
             activity?.SetActivityStatus(ActivityStatus.Error(e));
-            measure.SetError();
+            measure?.SetError();
 
             throw;
         }
     }
 
     protected async Task Trace(StreamName stream, string operation, Func<Task> task) {
         using var activity = StartActivity(stream, operation);
-        using var measure  = Measure.Start(MetricsSource, new PersistenceMetricsContext(ComponentName, operation));
+        using var measure  = StartMeasure(operation);
 
         try {
             await task().NoContext();
             activity?.SetActivityStatus(ActivityStatus.Ok());
         } catch (Exception e) {
             activity?.SetActivityStatus(ActivityStatus.Error(e));
-            measure.SetError();
+            measure?.SetError();
 
             throw;
         }
@@ -55,7 +55,7 @@ protected async IAsyncEnumerable<T> TraceEnumerable<T>(
             [EnumeratorCancellation] CancellationToken cancellationToken = default
         ) {
         using var activity = StartActivity(stream, operation);
-        using var measure  = Measure.Start(MetricsSource, new PersistenceMetricsContext(ComponentName, operation));
+        using var measure  = StartMeasure(operation);
 
         var enumerator = source.GetAsyncEnumerator(cancellationToken);
 
@@ -67,7 +67,7 @@ protected async IAsyncEnumerable<T> TraceEnumerable<T>(
                     moved = await enumerator.MoveNextAsync().NoContext();
                 } catch (Exception e) {
                     activity?.SetActivityStatus(ActivityStatus.Error(e));
-                    measure.SetError();
+                    measure?.SetError();
 
                     throw;
                 }
@@ -81,6 +81,12 @@ protected async IAsyncEnumerable<T> TraceEnumerable<T>(
         activity?.SetActivityStatus(ActivityStatus.Ok());
     }
 
+    // Nobody listening means nothing to record, so skip the measure and its context rather than allocate both.
+    private protected Measure? StartMeasure(string operation)
+        => MetricsSource.IsEnabled(Measure.EventName)
+            ? Measure.Start(MetricsSource, new PersistenceMetricsContext(ComponentName, operation))
+            : null;
+
     protected static Activity? StartActivity(StreamName stream, string operationName) {
         if (!EventuousDiagnostics.Enabled) return null;
 

src/Core/src/Eventuous.Persistence/Diagnostics/Tracing/TracedEventWriter.cs

@@ -5,7 +5,6 @@
 
 namespace Eventuous.Diagnostics.Tracing;
 
-using Metrics;
 using static Constants;
 
 public class TracedEventWriter(IEventWriter writer) : BaseTracer, IEventWriter {
@@ -21,8 +20,9 @@ CancellationToken                   cancellationToken
         ) {
         using var activity = StartActivity(stream, Operations.AppendEvents);
 
-        using var measure = Measure.Start(MetricsSource, new PersistenceMetricsContext(ComponentName, Operations.AppendEvents));
+        using var measure = StartMeasure(Operations.AppendEvents);
 
+        // Snapshot, so the inner writer can't see the caller change the collection while the append is in flight
         var tracedEvents = events
             .Select(x => x with { Metadata = x.Metadata.AddActivityTags(activity) })
             .ToArray();
@@ -34,7 +34,7 @@ CancellationToken                   cancellationToken
             return result;
         } catch (Exception e) {
             activity?.SetActivityStatus(ActivityStatus.Error(e));
-            measure.SetError();
+            measure?.SetError();
 
             throw;
         }
@@ -46,7 +46,7 @@ public async Task<AppendEventsResult[]> AppendEvents(IReadOnlyCollection<NewStre
         var       streamNames = new StreamName(string.Join(", ", appends.Select(a => a.StreamName.ToString())));
         using var activity    = StartActivity(streamNames, Operations.AppendEvents);
 
-        using var measure = Measure.Start(MetricsSource, new PersistenceMetricsContext(ComponentName, Operations.AppendEvents));
+        using var measure = StartMeasure(Operations.AppendEvents);
 
         var tracedAppends = appends.Select(a => a with { Events = [.. a.Events.Select(x => x with { Metadata = x.Metadata.AddActivityTags(activity) })] }).ToArray();
 
@@ -57,7 +57,7 @@ public async Task<AppendEventsResult[]> AppendEvents(IReadOnlyCollection<NewStre
             return results;
         } catch (Exception e) {
             activity?.SetActivityStatus(ActivityStatus.Error(e));
-            measure.SetError();
+            measure?.SetError();
 
             throw;
         }

src/Core/src/Eventuous.Serialization.Json.Dynamic/DefaultEventSerializer.cs

@@ -11,6 +11,11 @@ public class DefaultEventSerializer : IEventSerializer {
     const string DynamicSerializationMessage =
         "DefaultEventSerializer uses reflection-based System.Text.Json serialization. Use DefaultStaticEventSerializer with a JsonSerializerContext in trimmed or AOT applications.";
 
+    // Failure results are immutable, so one instance per error kind is shared instead of allocating per event
+    static readonly FailedToDeserialize UnknownType         = new(DeserializationError.UnknownType);
+    static readonly FailedToDeserialize ContentTypeMismatch = new(DeserializationError.ContentTypeMismatch);
+    static readonly FailedToDeserialize PayloadEmpty        = new(DeserializationError.PayloadEmpty);
+
     readonly JsonSerializerOptions _options;
     readonly ITypeMapper           _typeMapper;
 
@@ -29,14 +34,14 @@ public DefaultEventSerializer(JsonSerializerOptions options, ITypeMapper? typeMa
     public DeserializationResult DeserializeEvent(ReadOnlySpan<byte> data, string eventType, string contentType) {
         var typeMapped = _typeMapper.TryGetType(eventType, out var dataType);
 
-        if (!typeMapped) return new FailedToDeserialize(DeserializationError.UnknownType);
-        if (contentType != ContentType) return new FailedToDeserialize(DeserializationError.ContentTypeMismatch);
+        if (!typeMapped) return UnknownType;
+        if (contentType != ContentType) return ContentTypeMismatch;
 
         var deserialized = JsonSerializer.Deserialize(data, dataType!, _options);
 
         return deserialized != null
             ? new SuccessfullyDeserialized(deserialized)
-            : new FailedToDeserialize(DeserializationError.PayloadEmpty);
+            : PayloadEmpty;
     }
 
     [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "The constructor is annotated with RequiresUnreferencedCode, so an instance only exists if the caller acknowledged the requirement")]

src/Core/src/Eventuous.Serialization/DefaultStaticEventSerializer.cs

@@ -9,19 +9,24 @@ namespace Eventuous;
 
 [PublicAPI]
 public class DefaultStaticEventSerializer(JsonSerializerContext context, ITypeMapper? typeMapper = null) : IEventSerializer {
+    // Failure results are immutable, so one instance per error kind is shared instead of allocating per event
+    static readonly FailedToDeserialize UnknownType         = new(DeserializationError.UnknownType);
+    static readonly FailedToDeserialize ContentTypeMismatch = new(DeserializationError.ContentTypeMismatch);
+    static readonly FailedToDeserialize PayloadEmpty        = new(DeserializationError.PayloadEmpty);
+
     readonly ITypeMapper _typeMapper = typeMapper ?? TypeMap.Instance;
 
     public DeserializationResult DeserializeEvent(ReadOnlySpan<byte> data, string eventType, string contentType) {
         var typeMapped = _typeMapper.TryGetType(eventType, out var dataType);
 
-        if (!typeMapped) return new FailedToDeserialize(DeserializationError.UnknownType);
-        if (contentType != ContentType) return new FailedToDeserialize(DeserializationError.ContentTypeMismatch);
+        if (!typeMapped) return UnknownType;
+        if (contentType != ContentType) return ContentTypeMismatch;
 
         var deserialized = JsonSerializer.Deserialize(data, dataType!, context);
 
         return deserialized != null
             ? new SuccessfullyDeserialized(deserialized)
-            : new FailedToDeserialize(DeserializationError.PayloadEmpty);
+            : PayloadEmpty;
     }
 
     public SerializationResult SerializeEvent(object evt)

src/Core/src/Eventuous.Subscriptions/Consumers/DefaultConsumer.cs

@@ -8,10 +8,10 @@ namespace Eventuous.Subscriptions.Consumers;
 // ReSharper disable once ParameterTypeCanBeEnumerable.Local
 public class DefaultConsumer(IEventHandler[] eventHandlers) : IMessageConsumer {
     public async ValueTask Consume(IMessageConsumeContext context) {
-        var scope = new Dictionary<string, object> {
-            {"SubscriptionId", context.SubscriptionId},
-            {"Stream", context.Stream},
-            {"MessageType", context.MessageType}
+        var scope = new KeyValuePair<string, object>[] {
+            new("SubscriptionId", context.SubscriptionId),
+            new("Stream", context.Stream),
+            new("MessageType", context.MessageType)
         };
 
         using var _ = context.LogContext.Logger.BeginScope(scope);