[OpenTelemetry] Avoid enumerator allocations

[martincostello]

Changes

• Avoid allocating array when enumerating log scopes.
• Avoid allocating enumerator when sampling attributes are a list.

Found by investigating profile allocations in an application after upgrading to 1.18.0.

SamplingResultBenchmarks:

Method	Before (Allocated)	After (Allocated)	Difference	% Reduction
NoAttributes	328 B	328 B	0 B	0%
WithAttributeArray	672 B	640 B	-32 B	4.8%
WithAttributeList	752 B	720 B	-32 B	4.3%
Drop	328 B	328 B	0 B	0%
ParentBasedSampled	328 B	328 B	0 B	0%

Scope Benchmarks

Benchmark	Before Mean	After Mean	Delta Mean	Before Alloc	After Alloc
ForEachScope	35.84 ns	27.16 ns	-24%	144 B	56 B

Scope Benchmarks

using BenchmarkDotNet.Attributes;
using Microsoft.Extensions.Logging;
using OpenTelemetry.Logs;

namespace Benchmarks.Logs;

[MemoryDiagnoser]
public class LogScopeDictionaryBenchmarks
{
    private readonly LoggerExternalScopeProvider scopeProvider = new();

    private readonly Action<LogRecordScope, object> callback = (scope, state) =>
    {
        foreach (var scopeItem in scope)
        {
            _ = scopeItem.Key;
            _ = scopeItem.Value;
        }
    };

    private readonly LogRecord logRecord;

    public LogScopeDictionaryBenchmarks()
    {
        this.scopeProvider.Push(new Dictionary<string, object>
        {
            ["RequestId"] = "abc123",
            ["UserId"] = 42,
            ["TenantId"] = Guid.NewGuid(),
            ["StartedAt"] = DateTime.UtcNow,
        });

        this.logRecord = new LogRecord(
            this.scopeProvider,
            DateTime.UtcNow,
            "Benchmark",
            LogLevel.Information,
            0,
            "Message",
            null,
            null,
            null);
    }

    [Benchmark]
    public void ForEachScope()
    {
        this.logRecord.ForEachScope(this.callback!, null);
    }
}

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.48%. Comparing base (63d9cd1) to head (7094a07).
⚠️ Report is 21 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7681      +/-   ##
==========================================
+ Coverage   91.45%   91.48%   +0.02%     
==========================================
  Files         318      318              
  Lines       17867    17881      +14     
==========================================
+ Hits        16341    16358      +17     
+ Misses       1526     1523       -3     

Flag	Coverage Δ
unittests-Project-Experimental	91.57% <100.00%> (-0.01%)	⬇️
unittests-Project-Stable	91.55% <100.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/OpenTelemetry/Logs/LogRecordScope.cs	92.30% <100.00%> (+3.41%)	⬆️
src/OpenTelemetry/Trace/TracerProviderSdk.cs	97.36% <100.00%> (+0.04%)	⬆️

... and 1 file with indirect coverage changes

[Copilot]

Pull request overview

Optimizes hot-path enumeration in tracing and logging to reduce allocations.

Changes:

• Indexes sampling attribute lists without allocating enumerators.
• Streams non-list log scopes instead of materializing arrays.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/OpenTelemetry/Trace/TracerProviderSdk.cs	Adds list-aware sampling attribute iteration.
src/OpenTelemetry/Logs/LogRecordScope.cs	Delegates enumeration for non-list scopes.

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[opentelemetry-pr-dashboard]

Pull request dashboard status

Merged · refreshed 2026-09-01 08:17 UTC

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