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Merged
Kielek merged 8 commits into from
Dec 4, 2025
Merged

[OpenTelemetry] Move BucketLookup tree to AggregatorStore #6715

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a0ddbc6
Fixes ##5976
iliar-turdushev Sep 18, 2025
9c9c5d5
Merge branch 'main' into histogrambuckets_memory
iliar-turdushev Nov 24, 2025
85c972e
Move BucketLookup tree to AggregateStore
iliar-turdushev Nov 25, 2025
7934ab0
Update the changelog
iliar-turdushev Nov 26, 2025
358a59d
Merge branch 'main' into histogrambuckets_memory
iliar-turdushev Nov 26, 2025
697d90b
Update src/OpenTelemetry/CHANGELOG.md
iliar-turdushev Nov 27, 2025
43ba5d4
Merge branch 'main' into histogrambuckets_memory
Kielek Dec 4, 2025
7b27dcb
remove redundant private setter
Kielek Dec 4, 2025
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3 changes: 3 additions & 0 deletions src/OpenTelemetry/CHANGELOG.md
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Expand Up @@ -19,6 +19,9 @@ Notes](../../RELEASENOTES.md).
* Added support for `Meter.TelemetrySchemaUrl` property.
([#6714](https://github.com/open-telemetry/opentelemetry-dotnet/pull/6714))

* Improve performance and reduce memory consumption for metrics histograms.
([#6715](https://github.com/open-telemetry/opentelemetry-dotnet/pull/6715))

## 1.14.0

Released 2025-Nov-12
Expand Down
26 changes: 13 additions & 13 deletions src/OpenTelemetry/Metrics/AggregatorStore.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,7 @@ internal sealed class AggregatorStore
private readonly MetricPoint[] metricPoints;
private readonly int[] currentMetricPointBatch;
private readonly AggregationType aggType;
private readonly double[] histogramBounds;
private readonly HistogramExplicitBounds histogramExplicitBounds;
private readonly int exponentialHistogramMaxSize;
private readonly int exponentialHistogramMaxScale;
private readonly UpdateLongDelegate updateLongCallback;
Expand Down Expand Up @@ -74,7 +74,7 @@ internal AggregatorStore(
this.currentMetricPointBatch = new int[this.NumberOfMetricPoints];
this.aggType = aggType;
this.OutputDelta = temporality == AggregationTemporality.Delta;
this.histogramBounds = metricStreamIdentity.HistogramBucketBounds ?? FindDefaultHistogramBounds(in metricStreamIdentity);
this.histogramExplicitBounds = new(metricStreamIdentity.HistogramBucketBounds ?? FindDefaultHistogramBounds(in metricStreamIdentity));
this.exponentialHistogramMaxSize = metricStreamIdentity.ExponentialHistogramMaxSize;
this.exponentialHistogramMaxScale = metricStreamIdentity.ExponentialHistogramMaxScale;
this.StartTimeExclusive = DateTimeOffset.UtcNow;
Expand Down Expand Up @@ -143,7 +143,7 @@ internal AggregatorStore(

internal DateTimeOffset EndTimeInclusive { get; private set; }

internal double[] HistogramBounds => this.histogramBounds;
internal double[] HistogramBounds => this.histogramExplicitBounds.Bounds;

internal bool IsExemplarEnabled()
{
Expand Down Expand Up @@ -393,11 +393,11 @@ private void InitializeZeroTagPointIfNotInitialized()
if (this.OutputDelta)
{
var lookupData = new LookupData(0, Tags.EmptyTags, Tags.EmptyTags);
this.metricPoints[0] = new MetricPoint(this, this.aggType, null, this.histogramBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale, lookupData);
this.metricPoints[0] = new MetricPoint(this, this.aggType, null, this.histogramExplicitBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale, lookupData);
}
else
{
this.metricPoints[0] = new MetricPoint(this, this.aggType, null, this.histogramBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale);
this.metricPoints[0] = new MetricPoint(this, this.aggType, null, this.histogramExplicitBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale);
}

this.zeroTagMetricPointInitialized = true;
Expand All @@ -421,11 +421,11 @@ private void InitializeOverflowTagPointIfNotInitialized()
if (this.OutputDelta)
{
var lookupData = new LookupData(1, tags, tags);
this.metricPoints[1] = new MetricPoint(this, this.aggType, keyValuePairs, this.histogramBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale, lookupData);
this.metricPoints[1] = new MetricPoint(this, this.aggType, keyValuePairs, this.histogramExplicitBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale, lookupData);
}
else
{
this.metricPoints[1] = new MetricPoint(this, this.aggType, keyValuePairs, this.histogramBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale);
this.metricPoints[1] = new MetricPoint(this, this.aggType, keyValuePairs, this.histogramExplicitBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale);
}

this.overflowTagMetricPointInitialized = true;
Expand Down Expand Up @@ -494,7 +494,7 @@ private int LookupAggregatorStore(KeyValuePair<string, object?>[] tagKeysAndValu
}

ref var metricPoint = ref this.metricPoints[aggregatorIndex];
metricPoint = new MetricPoint(this, this.aggType, sortedTags.KeyValuePairs, this.histogramBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale);
metricPoint = new MetricPoint(this, this.aggType, sortedTags.KeyValuePairs, this.histogramExplicitBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale);

// Add to dictionary *after* initializing MetricPoint
// as other threads can start writing to the
Expand Down Expand Up @@ -543,7 +543,7 @@ private int LookupAggregatorStore(KeyValuePair<string, object?>[] tagKeysAndValu
}

ref var metricPoint = ref this.metricPoints[aggregatorIndex];
metricPoint = new MetricPoint(this, this.aggType, givenTags.KeyValuePairs, this.histogramBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale);
metricPoint = new MetricPoint(this, this.aggType, givenTags.KeyValuePairs, this.histogramExplicitBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale);

// Add to dictionary *after* initializing MetricPoint
// as other threads can start writing to the
Expand Down Expand Up @@ -619,7 +619,7 @@ private int LookupAggregatorStoreForDeltaWithReclaim(KeyValuePair<string, object
lookupData = new LookupData(index, sortedTags, givenTags);

ref var metricPoint = ref this.metricPoints[index];
metricPoint = new MetricPoint(this, this.aggType, sortedTags.KeyValuePairs, this.histogramBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale, lookupData);
metricPoint = new MetricPoint(this, this.aggType, sortedTags.KeyValuePairs, this.histogramExplicitBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale, lookupData);
newMetricPointCreated = true;

// Add to dictionary *after* initializing MetricPoint
Expand Down Expand Up @@ -665,7 +665,7 @@ private int LookupAggregatorStoreForDeltaWithReclaim(KeyValuePair<string, object
lookupData = new LookupData(index, Tags.EmptyTags, givenTags);

ref var metricPoint = ref this.metricPoints[index];
metricPoint = new MetricPoint(this, this.aggType, givenTags.KeyValuePairs, this.histogramBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale, lookupData);
metricPoint = new MetricPoint(this, this.aggType, givenTags.KeyValuePairs, this.histogramExplicitBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale, lookupData);
newMetricPointCreated = true;

// Add to dictionary *after* initializing MetricPoint
Expand Down Expand Up @@ -776,7 +776,7 @@ private bool TryGetAvailableMetricPointRare(
lookupData = new LookupData(index, sortedTags, givenTags);

ref var metricPoint = ref this.metricPoints[index];
metricPoint = new MetricPoint(this, this.aggType, sortedTags.KeyValuePairs, this.histogramBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale, lookupData);
metricPoint = new MetricPoint(this, this.aggType, sortedTags.KeyValuePairs, this.histogramExplicitBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale, lookupData);
newMetricPointCreated = true;

// Add to dictionary *after* initializing MetricPoint
Expand Down Expand Up @@ -807,7 +807,7 @@ private bool TryGetAvailableMetricPointRare(
lookupData = new LookupData(index, Tags.EmptyTags, givenTags);

ref var metricPoint = ref this.metricPoints[index];
metricPoint = new MetricPoint(this, this.aggType, givenTags.KeyValuePairs, this.histogramBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale, lookupData);
metricPoint = new MetricPoint(this, this.aggType, givenTags.KeyValuePairs, this.histogramExplicitBounds, this.exponentialHistogramMaxSize, this.exponentialHistogramMaxScale, lookupData);
newMetricPointCreated = true;

// Add to dictionary *after* initializing MetricPoint
Expand Down
128 changes: 128 additions & 0 deletions src/OpenTelemetry/Metrics/HistogramExplicitBounds.cs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,128 @@
// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0

using System.Diagnostics;
using System.Runtime.CompilerServices;

namespace OpenTelemetry.Metrics;

internal sealed class HistogramExplicitBounds
{
internal const int DefaultBoundaryCountForBinarySearch = 50;

private readonly BucketLookupNode? bucketLookupTreeRoot;
private readonly Func<double, int> findHistogramBucketIndex;

public HistogramExplicitBounds(double[] bounds)
{
this.Bounds = CleanUpInfinitiesFromExplicitBounds(bounds);
this.findHistogramBucketIndex = this.FindBucketIndexLinear;

if (this.Bounds.Length >= DefaultBoundaryCountForBinarySearch)
{
this.bucketLookupTreeRoot = ConstructBalancedBST(this.Bounds, 0, this.Bounds.Length);
this.findHistogramBucketIndex = this.FindBucketIndexBinary;

static BucketLookupNode? ConstructBalancedBST(double[] values, int min, int max)
{
if (min == max)
{
return null;
}

int median = min + ((max - min) / 2);
return new BucketLookupNode
{
Index = median,
UpperBoundInclusive = values[median],
LowerBoundExclusive = median > 0 ? values[median - 1] : double.NegativeInfinity,
Left = ConstructBalancedBST(values, min, median),
Right = ConstructBalancedBST(values, median + 1, max),
};
}
}
}

public double[] Bounds { get; }

[MethodImpl(MethodImplOptions.AggressiveInlining)]
public int FindBucketIndex(double value)
{
return this.findHistogramBucketIndex(value);
}

private static double[] CleanUpInfinitiesFromExplicitBounds(double[] bounds)
{
for (var i = 0; i < bounds.Length; i++)
{
if (double.IsNegativeInfinity(bounds[i]) || double.IsPositiveInfinity(bounds[i]))
Comment thread
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{
return bounds
.Where(b => !double.IsNegativeInfinity(b) && !double.IsPositiveInfinity(b))
.ToArray();
}
}

Comment on lines +56 to +65

Copilot AI Dec 4, 2025

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The CleanUpInfinitiesFromExplicitBounds method performs two passes over the array when infinities are found: first to detect them, then LINQ operations (Where + ToArray) to filter them. For better performance, consider collecting filtered values in a single pass using a List or ArrayPool, especially since this runs in the hot path during construction.

Suggested change
for (var i = 0; i < bounds.Length; i++)
{
if (double.IsNegativeInfinity(bounds[i]) || double.IsPositiveInfinity(bounds[i]))
{
return bounds
.Where(b => !double.IsNegativeInfinity(b) && !double.IsPositiveInfinity(b))
.ToArray();
}
}
List<double>? filtered = null;
for (var i = 0; i < bounds.Length; i++)
{
var b = bounds[i];
if (double.IsNegativeInfinity(b) || double.IsPositiveInfinity(b))
{
if (filtered == null)
{
filtered = new List<double>(bounds.Length - 1);
for (var j = 0; j < i; j++)
{
filtered.Add(bounds[j]);
}
}
// skip this value
}
else
{
if (filtered != null)
{
filtered.Add(b);
}
}
}
if (filtered != null)
{
return filtered.ToArray();
}

Copilot uses AI. Check for mistakes.
return bounds;
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
private int FindBucketIndexBinary(double value)
{
BucketLookupNode? current = this.bucketLookupTreeRoot;

Debug.Assert(current != null, "Bucket root was null.");

do
{
if (value <= current!.LowerBoundExclusive)
{
current = current.Left;
}
else if (value > current.UpperBoundInclusive)
{
current = current.Right;
}
else
{
return current.Index;
}
}
while (current != null);

Debug.Assert(this.Bounds != null, "ExplicitBounds was null.");
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return this.Bounds!.Length;
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}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
private int FindBucketIndexLinear(double value)
{
Debug.Assert(this.Bounds != null, "ExplicitBounds was null.");
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int i;
for (i = 0; i < this.Bounds!.Length; i++)
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{
// Upper bound is inclusive
if (value <= this.Bounds[i])
{
break;
}
}

return i;
}

private sealed class BucketLookupNode
{
public double UpperBoundInclusive { get; set; }

public double LowerBoundExclusive { get; set; }

public int Index { get; set; }

public BucketLookupNode? Left { get; set; }

public BucketLookupNode? Right { get; set; }
}
}
107 changes: 8 additions & 99 deletions src/OpenTelemetry/Metrics/MetricPoint/HistogramBuckets.cs
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Expand Up @@ -12,8 +12,6 @@ namespace OpenTelemetry.Metrics;
// Note: Does not implement IEnumerable<> to prevent accidental boxing.
public class HistogramBuckets
{
internal const int DefaultBoundaryCountForBinarySearch = 50;

internal readonly double[]? ExplicitBounds;

internal readonly HistogramBucketValues[] BucketCounts;
Expand All @@ -27,40 +25,13 @@ public class HistogramBuckets
internal double RunningMax = double.NegativeInfinity;
internal double SnapshotMax;

private readonly BucketLookupNode? bucketLookupTreeRoot;

private readonly Func<double, int> findHistogramBucketIndex;
private readonly HistogramExplicitBounds? histogramExplicitBounds;

internal HistogramBuckets(double[]? explicitBounds)
internal HistogramBuckets(HistogramExplicitBounds? histogramExplicitBounds)
{
explicitBounds = CleanUpInfinitiesFromExplicitBounds(explicitBounds);
this.ExplicitBounds = explicitBounds;
this.findHistogramBucketIndex = this.FindBucketIndexLinear;
if (explicitBounds != null && explicitBounds.Length >= DefaultBoundaryCountForBinarySearch)
{
this.bucketLookupTreeRoot = ConstructBalancedBST(explicitBounds, 0, explicitBounds.Length)!;
this.findHistogramBucketIndex = this.FindBucketIndexBinary;

static BucketLookupNode? ConstructBalancedBST(double[] values, int min, int max)
{
if (min == max)
{
return null;
}

int median = min + ((max - min) / 2);
return new BucketLookupNode
{
Index = median,
UpperBoundInclusive = values[median],
LowerBoundExclusive = median > 0 ? values[median - 1] : double.NegativeInfinity,
Left = ConstructBalancedBST(values, min, median),
Right = ConstructBalancedBST(values, median + 1, max),
};
}
}

this.BucketCounts = explicitBounds != null ? new HistogramBucketValues[explicitBounds.Length + 1] : Array.Empty<HistogramBucketValues>();
this.histogramExplicitBounds = histogramExplicitBounds;
this.ExplicitBounds = histogramExplicitBounds?.Bounds;
this.BucketCounts = this.ExplicitBounds != null ? new HistogramBucketValues[this.ExplicitBounds.Length + 1] : [];
}

/// <summary>
Expand All @@ -71,7 +42,7 @@ internal HistogramBuckets(double[]? explicitBounds)

internal HistogramBuckets Copy()
{
HistogramBuckets copy = new HistogramBuckets(this.ExplicitBounds);
HistogramBuckets copy = new HistogramBuckets(this.histogramExplicitBounds);

Array.Copy(this.BucketCounts, copy.BucketCounts, this.BucketCounts.Length);
copy.SnapshotSum = this.SnapshotSum;
Expand All @@ -84,54 +55,8 @@ internal HistogramBuckets Copy()
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal int FindBucketIndex(double value)
{
return this.findHistogramBucketIndex(value);
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal int FindBucketIndexBinary(double value)
{
BucketLookupNode? current = this.bucketLookupTreeRoot;

Debug.Assert(current != null, "Bucket root was null.");

do
{
if (value <= current!.LowerBoundExclusive)
{
current = current.Left;
}
else if (value > current.UpperBoundInclusive)
{
current = current.Right;
}
else
{
return current.Index;
}
}
while (current != null);

Debug.Assert(this.ExplicitBounds != null, "ExplicitBounds was null.");

return this.ExplicitBounds!.Length;
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal int FindBucketIndexLinear(double value)
{
Debug.Assert(this.ExplicitBounds != null, "ExplicitBounds was null.");

int i;
for (i = 0; i < this.ExplicitBounds!.Length; i++)
{
// Upper bound is inclusive
if (value <= this.ExplicitBounds[i])
{
break;
}
}

return i;
Debug.Assert(this.histogramExplicitBounds != null, "histogramExplicitBounds was null.");
return this.histogramExplicitBounds!.FindBucketIndex(value);
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
Expand Down Expand Up @@ -159,9 +84,6 @@ internal void Snapshot(bool outputDelta)
}
}

private static double[]? CleanUpInfinitiesFromExplicitBounds(double[]? explicitBounds) => explicitBounds
?.Where(b => !double.IsNegativeInfinity(b) && !double.IsPositiveInfinity(b)).ToArray();

/// <summary>
/// Enumerates the elements of a <see cref="HistogramBuckets"/>.
/// </summary>
Expand Down Expand Up @@ -217,17 +139,4 @@ internal struct HistogramBucketValues
public long RunningValue;
public long SnapshotValue;
}

private sealed class BucketLookupNode
{
public double UpperBoundInclusive { get; set; }

public double LowerBoundExclusive { get; set; }

public int Index { get; set; }

public BucketLookupNode? Left { get; set; }

public BucketLookupNode? Right { get; set; }
}
}
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