ref: Instantiating _tags for Spans lazily (#2636)

Author: bitsandfoxes

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Features
 
+- Reduced the memory footprint of `SpanTracer` by initializing the tags lazily ([2636](https://github.com/getsentry/sentry-dotnet/pull/2636))
 - Added distributed tracing without performance for Azure Function Workers ([#2630](https://github.com/getsentry/sentry-dotnet/pull/2630))
 - The SDK now provides and overload of `ContinueTrace` that accepts headers as `string` ([#2601](https://github.com/getsentry/sentry-dotnet/pull/2601))
 - Sentry tracing middleware now gets configured automatically ([#2602](https://github.com/getsentry/sentry-dotnet/pull/2602))

benchmarks/Sentry.Benchmarks/TransactionBenchmarks.cs

@@ -0,0 +1,34 @@
+using BenchmarkDotNet.Attributes;
+
+namespace Sentry.Benchmarks;
+
+public class TransactionBenchmarks
+{
+    private const string Operation = "Operation";
+    private const string Name = "Name";
+
+    [Params(1, 10, 100, 1000)]
+    public int SpanCount;
+
+    private IDisposable _sdk;
+
+    [GlobalSetup(Target = nameof(CreateTransaction))]
+    public void EnabledSdk() => _sdk = SentrySdk.Init(Constants.ValidDsn);
+
+    [GlobalCleanup(Target = nameof(CreateTransaction))]
+    public void DisableDsk() => _sdk.Dispose();
+
+    [Benchmark(Description = "Creates a Transaction")]
+    public void CreateTransaction()
+    {
+        var transaction = SentrySdk.StartTransaction(Name, Operation);
+
+        for (var i = 0; i < SpanCount; i++)
+        {
+            var span = transaction.StartChild(Operation);
+            span.Finish();
+        }
+
+        transaction.Finish();
+    }
+}

src/Sentry/Span.cs

@@ -88,7 +88,7 @@ public Span(ISpan tracer)
         Status = tracer.Status;
         IsSampled = tracer.IsSampled;
         _extra = tracer.Extra.ToDictionary();
-        _tags = tracer.Tags.ToDictionary();
+        _tags = tracer is SpanTracer s ? s.InternalTags?.ToDictionary() : tracer.Tags.ToDictionary();
     }
 
     /// <inheritdoc />

src/Sentry/SpanTracer.cs

@@ -52,6 +52,8 @@ public class SpanTracer : ISpan
 
     private ConcurrentDictionary<string, string>? _tags;
 
+    internal ConcurrentDictionary<string, string>? InternalTags => _tags;
+
     /// <inheritdoc />
     public IReadOnlyDictionary<string, string> Tags => _tags ??= new ConcurrentDictionary<string, string>();