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fix(backport): memory leak when finishing unsampled Transactions/Spans #4853

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Merged
Flash0ver merged 2 commits into from
Jan 23, 2026
Merged

fix(backport): memory leak when finishing unsampled Transactions/Spans #4853

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8184dd0
fix(backport): memory leak when finishing unsampled Transactions/Spans
Flash0ver Jan 21, 2026
29e2d7b
docs: update CHANGELOG.md
Flash0ver Jan 21, 2026
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5 changes: 5 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -2,6 +2,11 @@

## Unreleased

### Fixes

- Memory leak when finishing an unsampled Transaction that has started unsampled Spans ([#4717](https://github.com/getsentry/sentry-dotnet/pull/4717))
- backported via ([#4853](https://github.com/getsentry/sentry-dotnet/pull/4853))

### Dependencies

- Bump Java SDK from v8.24.0 to v8.25.0 ([#4679](https://github.com/getsentry/sentry-dotnet/pull/4679))
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19 changes: 18 additions & 1 deletion src/Sentry/Internal/UnsampledTransaction.cs
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Expand Up @@ -4,15 +4,20 @@ namespace Sentry.Internal;

/// <summary>
/// We know already, when starting a transaction, whether it's going to be sampled or not. When it's not sampled, we can
/// avoid lots of unecessary processing. The only thing we need to track is the number of spans that would have been
/// avoid lots of unnecessary processing. The only thing we need to track is the number of spans that would have been
/// created (the client reports detailing discarded events includes this detail).
/// </summary>
internal sealed class UnsampledTransaction : NoOpTransaction
{
// Although it's a little bit wasteful to create separate individual class instances here when all we're going to
// report to sentry is the span count (in the client report), SDK users may refer to things like
// `ITransaction.Spans.Count`, so we create an actual collection
#if NETCOREAPP2_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
private readonly ConcurrentBag<ISpan> _spans = [];
#else
private ConcurrentBag<ISpan> _spans = [];
#endif

private readonly IHub _hub;
private readonly ITransactionContext _context;
private readonly SentryOptions? _options;
Expand Down Expand Up @@ -79,6 +84,9 @@ public override void Finish()
_options?.ClientReportRecorder.RecordDiscardedEvent(discardReason, DataCategory.Span, spanCount);

_options?.LogDebug("Finished unsampled transaction");

// Release tracked spans
ReleaseSpans();
}

public override void Finish(SpanStatus status) => Finish();
Expand All @@ -103,4 +111,13 @@ public ISpan StartChild(string operation, SpanId spanId)
_spans.Add(span);
return span;
}

private void ReleaseSpans()
{
#if NETCOREAPP2_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
_spans.Clear();
#else
_spans = [];
#endif
}
}
4 changes: 2 additions & 2 deletions src/Sentry/TransactionTracer.cs
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Expand Up @@ -167,7 +167,7 @@ public IReadOnlyList<string> Fingerprint
/// <inheritdoc />
public IReadOnlyDictionary<string, string> Tags => _tags;

#if NETSTANDARD2_1_OR_GREATER
#if NETCOREAPP2_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
private readonly ConcurrentBag<ISpan> _spans = new();
#else
private ConcurrentBag<ISpan> _spans = new();
Expand Down Expand Up @@ -429,7 +429,7 @@ public string? Origin

private void ReleaseSpans()
{
#if NETSTANDARD2_1_OR_GREATER
#if NETCOREAPP2_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
_spans.Clear();
#else
_spans = new ConcurrentBag<ISpan>();
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18 changes: 18 additions & 0 deletions test/Sentry.Tests/Internals/UnsampledSpanTests.cs
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Expand Up @@ -2,6 +2,24 @@ namespace Sentry.Tests.Internals;

public class UnsampledSpanTests
{
[Fact]
public void StartChild_IsUnsampledSpan_HasReferenceToUnsampledTransaction()
{
// Arrange
var hub = Substitute.For<IHub>();
ITransactionContext context = new TransactionContext("TestTransaction", "TestOperation",
new SentryTraceHeader(SentryId.Create(), SpanId.Create(), false)
);
var transaction = new UnsampledTransaction(hub, context);

// Act
var unsampledSpan = transaction.StartChild("Foo");

// Assert
Assert.IsType<UnsampledSpan>(unsampledSpan);
Assert.Same(transaction, unsampledSpan.GetTransaction());
}

[Fact]
public void GetTraceHeader_CreatesHeaderFromUnsampledTransaction()
{
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40 changes: 40 additions & 0 deletions test/Sentry.Tests/Internals/UnsampledTransactionTests.cs
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@@ -0,0 +1,40 @@
namespace Sentry.Tests.Internals;

public class UnsampledTransactionTests
{
[Fact]
public void StartChild_CreatesSpan_IsTrackedByParent()
{
// Arrange
var hub = Substitute.For<IHub>();
ITransactionContext context = new TransactionContext("TestTransaction", "TestOperation",
new SentryTraceHeader(SentryId.Create(), SpanId.Create(), false)
);
var transaction = new UnsampledTransaction(hub, context);

// Act
var unsampledSpan = transaction.StartChild("Foo");

// Assert
var span = Assert.Single(transaction.Spans);
Assert.Same(unsampledSpan, span);
}

[Fact]
public void Finish_WithTrackedSpans_ClearsTrackedSpans()
{
// Arrange
var hub = Substitute.For<IHub>();
ITransactionContext context = new TransactionContext("TestTransaction", "TestOperation",
new SentryTraceHeader(SentryId.Create(), SpanId.Create(), false)
);
var transaction = new UnsampledTransaction(hub, context);
_ = transaction.StartChild("Foo");

// Act
transaction.Finish();

// Assert
Assert.Empty(transaction.Spans);
}
}
6 changes: 3 additions & 3 deletions test/Sentry.Tests/SpanTracerTests.cs
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Expand Up @@ -10,7 +10,7 @@ public async Task SetExtra_DataInserted_NoDataLoss()
{
// Arrange
var hub = Substitute.For<IHub>();
var transaction = new SpanTracer(hub, null, null, SentryId.Empty, "");
var spanTracer = new SpanTracer(hub, null, null, SentryId.Empty, "");
var evt = new ManualResetEvent(false);
var ready = new ManualResetEvent(false);
var counter = 0;
Expand All @@ -27,7 +27,7 @@ public async Task SetExtra_DataInserted_NoDataLoss()

for (var i = 0; i < amount; i++)
{
transaction.SetExtra(Guid.NewGuid().ToString(), Guid.NewGuid());
spanTracer.SetExtra(Guid.NewGuid().ToString(), Guid.NewGuid());
}
})).ToList();
ready.WaitOne();
Expand All @@ -36,7 +36,7 @@ public async Task SetExtra_DataInserted_NoDataLoss()

// Arrange
// 4 tasks testing X amount should be the same amount as Extras.
Assert.Equal(4 * amount, transaction.Extra.Count);
Assert.Equal(4 * amount, spanTracer.Extra.Count);
}
}
}
35 changes: 35 additions & 0 deletions test/Sentry.Tests/TransactionTracerTests.cs
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@@ -0,0 +1,35 @@
namespace Sentry.Tests;

public class TransactionTracerTests
{
[Fact]
public void StartChild_CreatesSpanTracer_TracksSpans()
{
// Arrange
var hub = Substitute.For<IHub>();
var transaction = new TransactionTracer(hub, "op", "name");

// Act
var span = transaction.StartChild("operation");

// Assert
Assert.IsType<SpanTracer>(span);
Assert.Collection(transaction.Spans,
element => Assert.Same(span, element));
}

[Fact]
public void Finish_WithTrackedSpans_ClearsTrackedSpans()
{
// Arrange
var hub = Substitute.For<IHub>();
var transaction = new TransactionTracer(hub, "op", "name");
_ = transaction.StartChild("operation");

// Act
transaction.Finish();

// Assert
Assert.Empty(transaction.Spans);
}
}
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