[Exporter.Prometheus] Improve performance by martincostello · Pull Request #7170 · open-telemetry/opentelemetry-dotnet

martincostello · 2026-04-25T19:27:16Z

Changes

Improve the performance of PrometheusSerializer by:
- Using SearchValues<T> on .NET 8+
- Writing common label value types directly instead of relying on ToString()
- Formatting numeric values directly as UTF-8 on .NET 8+
- Caching serialized metric names, metadata names, units, and static tag prefixes
- Reusing serialized tags across histogram bucket/sum/count output
- Use stackalloc for small temporary tag buffers on .NET 8+

Benchmark Results

See #7170 (comment) for latest results.

Details

Copilot Summary

Overall duration: PrometheusSerializer-perf is 0.833x geometric mean versus main.
Allocations: unchanged in all 3 cases (0.0% / 1.00x).

Per-config summary

Config	Method	Duration change	Allocation change
`NumberOfSerializeCalls=1`	`WriteMetric`	-16.1% / 0.839x	0.0% / 1.00x
`NumberOfSerializeCalls=1000`	`WriteMetric`	-20.1% / 0.799x	0.0% / 1.00x
`NumberOfSerializeCalls=10000`	`WriteMetric`	-13.9% / 0.861x	0.0% / 1.00x

Takeaways

PrometheusSerializer-perf shows consistent runtime improvement.

Detailed Results

Expand to view

main


BenchmarkDotNet v0.15.8, Windows 11 (10.0.26200.8246/25H2/2025Update/HudsonValley2)
13th Gen Intel Core i7-13700H 2.90GHz, 1 CPU, 20 logical and 14 physical cores
.NET SDK 10.0.203
  [Host]    : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3
  .NET 10.0 : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3

Job=.NET 10.0  Runtime=.NET 10.0  Toolchain=net10.0

Method	NumberOfSerializeCalls	Mean	Error	StdDev	Allocated
WriteMetric	1	3.365 μs	0.0672 μs	0.1262 μs	-
WriteMetric	1000	3,559.816 μs	69.3908 μs	121.5324 μs	-
WriteMetric	10000	32,891.695 μs	582.1268 μs	940.0263 μs	-

This PR


BenchmarkDotNet v0.15.8, Windows 11 (10.0.26200.8246/25H2/2025Update/HudsonValley2)
13th Gen Intel Core i7-13700H 2.90GHz, 1 CPU, 20 logical and 14 physical cores
.NET SDK 10.0.203
  [Host]    : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3
  .NET 10.0 : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3

Job=.NET 10.0  Runtime=.NET 10.0  Toolchain=net10.0

Method	NumberOfSerializeCalls	Mean	Error	StdDev	Allocated
WriteMetric	1	2.823 μs	0.0561 μs	0.0873 μs	-
WriteMetric	1000	2,844.279 μs	55.7913 μs	97.7139 μs	-
WriteMetric	10000	28,306.433 μs	561.5490 μs	922.6411 μs	-

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)~~

- Improve the performance of `PrometheusSerializer` for .NET 8+ by using `SearchValues<T>`. - Add fuzz tests for `PrometheusSerializer`.

codecov · 2026-04-25T19:30:49Z

Codecov Report

❌ Patch coverage is 88.85630% with 38 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.59%. Comparing base (7e29276) to head (c24c7ed).
⚠️ Report is 36 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...heus.HttpListener/Internal/PrometheusSerializer.cs	87.40%	32 Missing ⚠️
...s.HttpListener/Internal/PrometheusSerializerExt.cs	93.93%	4 Missing ⚠️
...tpListener/Internal/PrometheusCollectionManager.cs	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7170      +/-   ##
==========================================
- Coverage   89.69%   89.59%   -0.11%     
==========================================
  Files         272      272              
  Lines       13366    13590     +224     
==========================================
+ Hits        11989    12176     +187     
- Misses       1377     1414      +37

Flag	Coverage Δ
unittests-Project-Experimental	`89.57% <88.85%> (-0.12%)`	⬇️
unittests-Project-Stable	`89.52% <88.85%> (-0.14%)`	⬇️
unittests-UnstableCoreLibraries-Experimental	`42.36% <88.26%> (+1.05%)`	⬆️

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

Files with missing lines	Coverage Δ
...ometheus.HttpListener/Internal/PrometheusMetric.cs	`99.42% <100.00%> (+0.05%)`	⬆️
...tpListener/Internal/PrometheusCollectionManager.cs	`87.58% <50.00%> (ø)`
...s.HttpListener/Internal/PrometheusSerializerExt.cs	`94.87% <93.93%> (-5.13%)`	⬇️
...heus.HttpListener/Internal/PrometheusSerializer.cs	`90.16% <87.40%> (-7.72%)`	⬇️

... and 1 file with indirect coverage changes

Handle buffer resize.

Handle different exception type between .NET and .NET Framework.

Copilot

Pull request overview

Improves the runtime performance of the Prometheus HttpListener exporter’s serialization path on .NET 8+ by using SearchValues<T>-based scanning and span-based UTF-8 writes, and adds new fuzz/property tests to validate serializer behavior.

Changes:

Optimize PrometheusSerializer string/number writing on .NET 8+ using SearchValues<char> and Encoding.UTF8.GetBytes(ReadOnlySpan<char>, Span<byte>).
Update collection retry logic to also treat ArgumentException as a “buffer too small” signal (in addition to IndexOutOfRangeException).
Add new unit tests and a new FsCheck-based fuzz test project for PrometheusSerializer.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/PrometheusSerializerTests.cs	Adds focused tests for ASCII writing, escaping behavior, and UTF-16 code-unit preservation.
test/OpenTelemetry.Exporter.Prometheus.HttpListener.FuzzTests/PrometheusSerializerFuzzTests.cs	Adds property-based tests comparing serializer outputs to reference implementations.
test/OpenTelemetry.Exporter.Prometheus.HttpListener.FuzzTests/OpenTelemetry.Exporter.Prometheus.HttpListener.FuzzTests.csproj	Introduces new fuzz test project referencing the HttpListener exporter and FsCheck.Xunit.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/OpenTelemetry.Exporter.Prometheus.HttpListener.csproj	Adds `InternalsVisibleTo` for the new fuzz test assembly.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusSerializer.cs	Implements .NET 8+ optimized escaping/writing using `SearchValues<char>` and span-based UTF-8 encoding.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusCollectionManager.cs	Broadens retryable exceptions to include `ArgumentException` (buffer too small from span-based UTF-8 encoding).
OpenTelemetry.slnx	Adds the new fuzz test project to the solution.

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Update comment.

Improve `PrometheusSerializer` performance further by: - Writing common label value types directly instead of relying on `ToString()` - Formatting numeric values directly as UTF-8 on .NET 8+ - Caching serialized metric names, metadata names, units, and static tag prefixes - Reusing serialized tags across histogram bucket/sum/count output - Use `stackalloc` for small temporary tag buffers on .NET 8+

Add missing patch coverage.

Encode the strings.

Add missing coverage for static labels.

Add remaining (easy) coverage and remove unused code.

Remove now-unused parameters from benchmarks.

Use helper for ASCII checking.

Fix some test changes that were removed during merge.

Fix broken UTF-8 tests.

Factor away some duplicated code paths.

Tidy up some of the formatting.

Add polyfills for `char`'s `IsAsciiDigit`, `IsAsciiLetterOrDigit` and `IsAsciiLetterLower` methods and remove helpers.

martincostello · 2026-04-28T17:15:18Z

Latest Benchmarks

TL;DR

This PR compared to main serializes metrics:

~40-70% faster and reduces allocations to effectively zero on net10.0
~10-50% faster with no changes to allocations on net462

Percentages vary by scenario.

Copilot Summary

Benchmark summary: `main` vs `PrometheusSerializer-perf`

PrometheusSerializer-perf is faster in every common benchmark case (18/18).

The biggest wins are on .NET 10.0:
- WriteHistogramMetric: 67.2%-70.3% faster (0.30x-0.33x duration ratio)
- WriteMetric: 61.8%-63.8% faster (0.36x-0.38x duration ratio)
- WriteMetricWithTypedLabels: 40.8%-46.2% faster (0.54x-0.59x duration ratio)
Allocations on .NET 10.0 also improve significantly:
- WriteMetric drops from 104 B / 104000 B / 1040000 B on main to 0 B / 0 B / 13 B
- WriteMetricWithTypedLabels drops from 104 B / 104000 B / 1040000 B on main to 0 B in all cases
On .NET Framework 4.6.2, runtime improves in every case too, but allocations are effectively unchanged.

High-level takeaways

All common suites improved
.NET 10.0 shows both large runtime wins and major allocation reductions
.NET Framework 4.6.2 shows clear runtime wins, with allocations essentially flat

Comparison table - expand to view

Ratios below are PrometheusSerializer-perf / main, so values below 1.00x are improvements.

Runtime	Method	Calls	Duration (`main` -> `perf`)	Duration change	Duration ratio	Allocations (`main` -> `perf`)	Allocation change	Allocation ratio
.NET 10.0	WriteMetric	1	4046.1 ns -> 1464.5 ns	-63.8%	0.36x	104 B -> 0 B	-100.0%	0.00x
.NET 10.0	WriteMetric	1000	4010806.8 ns -> 1456272.4 ns	-63.7%	0.36x	104000 B -> 0B	-100.0%	0.00x
.NET 10.0	WriteMetric	10000	40214670.5 ns -> 15353037.5 ns	-61.8%	0.38x	1040000 B -> 13 B	-99.9988%	0.00001x
.NET 10.0	WriteHistogramMetric	1	3411.9 ns -> 1011.9 ns	-70.3%	0.30x	0 B -> 0 B	0.0%	1.00x
.NET 10.0	WriteHistogramMetric	1000	3238743.2 ns -> 1024652.2 ns	-68.4%	0.32x	0 B -> 0 B	0.0%	1.00x
.NET 10.0	WriteHistogramMetric	10000	32792324.8 ns -> 10747484.1 ns	-67.2%	0.33x	0 B -> 0 B	0.0%	1.00x
.NET 10.0	WriteMetricWithTypedLabels	1	331.3 ns -> 178.4 ns	-46.2%	0.54x	104 B -> 0 B	-100.0%	0.00x
.NET 10.0	WriteMetricWithTypedLabels	1000	334419.5 ns -> 182936.2 ns	-45.3%	0.55x	104000 B -> 0 B	-100.0%	0.00x
.NET 10.0	WriteMetricWithTypedLabels	10000	3279539.7 ns -> 1940527.0 ns	-40.8%	0.59x	1040000 B -> 0 B	-100.0%	0.00x
.NET Framework 4.6.2	WriteMetric	1	9941.7 ns -> 5508.3 ns	-44.6%	0.55x	1492 B -> 1492 B	0.0%	1.00x
.NET Framework 4.6.2	WriteMetric	1000	9849356.6 ns -> 6332700.4 ns	-35.7%	0.64x	1492365 B -> 1492366 B	+0.00007%	1.00x
.NET Framework 4.6.2	WriteMetric	10000	96584934.4 ns -> 62290357.0 ns	-35.5%	0.64x	14923224 B -> 14923223 B	-0.000007%	1.00x
.NET Framework 4.6.2	WriteHistogramMetric	1	7650.7 ns -> 3948.3 ns	-48.4%	0.52x	1147 B -> 1147 B	0.0%	1.00x
.NET Framework 4.6.2	WriteHistogramMetric	1000	7491491.4 ns -> 4271289.0 ns	-43.0%	0.57x	1147338 B -> 1147338 B	0.0%	1.00x
.NET Framework 4.6.2	WriteHistogramMetric	10000	76410881.0 ns -> 43874466.7 ns	-42.6%	0.57x	11473577 B -> 11473677 B	+0.00087%	1.00x
.NET Framework 4.6.2	WriteMetricWithTypedLabels	1	731.9 ns -> 624.0 ns	-14.7%	0.85x	185 B -> 185 B	0.0%	1.00x
.NET Framework 4.6.2	WriteMetricWithTypedLabels	1000	741720.2 ns -> 659912.7 ns	-11.0%	0.89x	184538 B -> 184538 B	0.0%	1.00x
.NET Framework 4.6.2	WriteMetricWithTypedLabels	10000	7470659.1 ns -> 6701965.1 ns	-10.3%	0.90x	1845397 B -> 1845397 B	0.0%	1.00x

Benchmark Results

Expand to view

main

BenchmarkDotNet v0.15.8, Windows 11 (10.0.26200.8246/25H2/2025Update/HudsonValley2)
13th Gen Intel Core i7-13700H 2.90GHz, 1 CPU, 20 logical and 14 physical cores
.NET SDK 10.0.203
  [Host]               : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3
  .NET 10.0            : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3
  .NET Framework 4.6.2 : .NET Framework 4.8.1 (4.8.9325.0), X64 RyuJIT VectorSize=256

Method	Job	Runtime	NumberOfSerializeCalls	Mean	Error	StdDev	Ratio	RatioSD	Gen0	Allocated	Alloc Ratio
WriteMetric	.NET 10.0	.NET 10.0	1	4,046.1 ns	80.81 ns	141.54 ns	1.00	0.05	0.0076	104 B	1.00
WriteMetric	.NET Framework 4.6.2	.NET Framework 4.6.2	1	9,941.7 ns	88.45 ns	82.74 ns	2.46	0.09	0.2289	1492 B	14.35

WriteHistogramMetric	.NET 10.0	.NET 10.0	1	3,411.9 ns	5.02 ns	3.92 ns	1.00	0.00	-	-	NA
WriteHistogramMetric	.NET Framework 4.6.2	.NET Framework 4.6.2	1	7,650.7 ns	78.25 ns	73.19 ns	2.24	0.02	0.1678	1147 B	NA

WriteMetricWithTypedLabels	.NET 10.0	.NET 10.0	1	331.3 ns	3.90 ns	3.65 ns	1.00	0.02	0.0081	104 B	1.00
WriteMetricWithTypedLabels	.NET Framework 4.6.2	.NET Framework 4.6.2	1	731.9 ns	9.84 ns	9.21 ns	2.21	0.04	0.0286	185 B	1.78

WriteMetric	.NET 10.0	.NET 10.0	1000	4,010,806.8 ns	78,737.36 ns	133,702.02 ns	1.00	0.05	7.8125	104000 B	1.00
WriteMetric	.NET Framework 4.6.2	.NET Framework 4.6.2	1000	9,849,356.6 ns	36,155.93 ns	30,191.84 ns	2.46	0.08	234.3750	1492365 B	14.35

WriteHistogramMetric	.NET 10.0	.NET 10.0	1000	3,238,743.2 ns	9,025.53 ns	8,442.49 ns	1.00	0.00	-	-	NA
WriteHistogramMetric	.NET Framework 4.6.2	.NET Framework 4.6.2	1000	7,491,491.4 ns	84,946.24 ns	79,458.77 ns	2.31	0.02	179.6875	1147338 B	NA

WriteMetricWithTypedLabels	.NET 10.0	.NET 10.0	1000	334,419.5 ns	3,451.25 ns	3,228.30 ns	1.00	0.01	7.8125	104000 B	1.00
WriteMetricWithTypedLabels	.NET Framework 4.6.2	.NET Framework 4.6.2	1000	741,720.2 ns	4,232.27 ns	3,751.80 ns	2.22	0.02	29.2969	184538 B	1.77

WriteMetric	.NET 10.0	.NET 10.0	10000	40,214,670.5 ns	791,163.59 ns	1,056,180.76 ns	1.00	0.04	76.9231	1040000 B	1.00
WriteMetric	.NET Framework 4.6.2	.NET Framework 4.6.2	10000	96,584,934.4 ns	246,936.38 ns	230,984.44 ns	2.40	0.06	2333.3333	14923224 B	14.35

WriteHistogramMetric	.NET 10.0	.NET 10.0	10000	32,792,324.8 ns	642,673.18 ns	921,702.74 ns	1.00	0.04	-	-	NA
WriteHistogramMetric	.NET Framework 4.6.2	.NET Framework 4.6.2	10000	76,410,881.0 ns	210,803.87 ns	197,186.07 ns	2.33	0.07	1714.2857	11473577 B	NA

WriteMetricWithTypedLabels	.NET 10.0	.NET 10.0	10000	3,279,539.7 ns	25,928.04 ns	22,984.53 ns	1.00	0.01	82.0313	1040000 B	1.00
WriteMetricWithTypedLabels	.NET Framework 4.6.2	.NET Framework 4.6.2	10000	7,470,659.1 ns	49,956.53 ns	41,715.97 ns	2.28	0.02	289.0625	1845397 B	1.77

This PR

BenchmarkDotNet v0.15.8, Windows 11 (10.0.26200.8246/25H2/2025Update/HudsonValley2)
13th Gen Intel Core i7-13700H 2.90GHz, 1 CPU, 20 logical and 14 physical cores
.NET SDK 10.0.203
  [Host]               : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3
  .NET 10.0            : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3
  .NET Framework 4.6.2 : .NET Framework 4.8.1 (4.8.9325.0), X64 RyuJIT VectorSize=256

Method	Job	Runtime	NumberOfSerializeCalls	Mean	Error	StdDev	Median	Ratio	RatioSD	Gen0	Allocated	Alloc Ratio
WriteMetric	.NET 10.0	.NET 10.0	1	1,464.5 ns	28.59 ns	50.82 ns	1,455.9 ns	1.00	0.05	-	-	NA
WriteMetric	.NET Framework 4.6.2	.NET Framework 4.6.2	1	5,508.3 ns	109.06 ns	176.11 ns	5,424.7 ns	3.77	0.17	0.2365	1492 B	NA

WriteHistogramMetric	.NET 10.0	.NET 10.0	1	1,011.9 ns	19.88 ns	33.22 ns	991.0 ns	1.00	0.05	-	-	NA
WriteHistogramMetric	.NET Framework 4.6.2	.NET Framework 4.6.2	1	3,948.3 ns	78.58 ns	143.69 ns	3,902.1 ns	3.91	0.19	0.1755	1147 B	NA

WriteMetricWithTypedLabels	.NET 10.0	.NET 10.0	1	178.4 ns	3.54 ns	6.10 ns	180.2 ns	1.00	0.05	-	-	NA
WriteMetricWithTypedLabels	.NET Framework 4.6.2	.NET Framework 4.6.2	1	624.0 ns	12.49 ns	20.51 ns	634.8 ns	3.50	0.16	0.0286	185 B	NA

WriteMetric	.NET 10.0	.NET 10.0	1000	1,456,272.4 ns	28,990.07 ns	47,631.52 ns	1,428,828.1 ns	1.00	0.05	-	-	NA
WriteMetric	.NET Framework 4.6.2	.NET Framework 4.6.2	1000	6,332,700.4 ns	71,098.90 ns	66,505.95 ns	6,296,635.2 ns	4.35	0.14	234.3750	1492366 B	NA

WriteHistogramMetric	.NET 10.0	.NET 10.0	1000	1,024,652.2 ns	20,310.62 ns	33,934.48 ns	1,003,637.6 ns	1.00	0.05	-	-	NA
WriteHistogramMetric	.NET Framework 4.6.2	.NET Framework 4.6.2	1000	4,271,289.0 ns	82,968.91 ns	81,486.57 ns	4,223,455.1 ns	4.17	0.16	179.6875	1147338 B	NA

WriteMetricWithTypedLabels	.NET 10.0	.NET 10.0	1000	182,936.2 ns	3,652.25 ns	5,577.37 ns	184,753.9 ns	1.00	0.04	-	-	NA
WriteMetricWithTypedLabels	.NET Framework 4.6.2	.NET Framework 4.6.2	1000	659,912.7 ns	6,925.20 ns	6,477.84 ns	663,846.5 ns	3.61	0.11	29.2969	184538 B	NA

WriteMetric	.NET 10.0	.NET 10.0	10000	15,353,037.5 ns	304,241.36 ns	711,154.41 ns	15,865,493.8 ns	1.00	0.07	-	13 B	1.00
WriteMetric	.NET Framework 4.6.2	.NET Framework 4.6.2	10000	62,290,357.0 ns	175,519.99 ns	164,181.51 ns	62,289,211.1 ns	4.07	0.19	2333.3333	14923223 B	1,147,940.23

WriteHistogramMetric	.NET 10.0	.NET 10.0	10000	10,747,484.1 ns	44,403.20 ns	34,667.10 ns	10,741,144.5 ns	1.00	0.00	-	-	NA
WriteHistogramMetric	.NET Framework 4.6.2	.NET Framework 4.6.2	10000	43,874,466.7 ns	59,774.99 ns	49,914.83 ns	43,880,050.0 ns	4.08	0.01	1750.0000	11473677 B	NA

WriteMetricWithTypedLabels	.NET 10.0	.NET 10.0	10000	1,940,527.0 ns	26,452.40 ns	24,743.59 ns	1,924,872.9 ns	1.00	0.02	-	-	NA
WriteMetricWithTypedLabels	.NET Framework 4.6.2	.NET Framework 4.6.2	10000	6,701,965.1 ns	84,667.47 ns	79,198.00 ns	6,655,671.1 ns	3.45	0.06	289.0625	1845397 B	NA

martincostello · 2026-04-28T17:23:18Z

Will rebase on top of #7194.

Copilot

Pull request overview

This PR focuses on improving the runtime performance of the Prometheus HttpListener exporter’s serialization path (especially PrometheusSerializer) by reducing per-write overhead and enabling more reuse/caching, and it adds fuzz testing to validate serializer behavior.

Changes:

Optimizes serialization by using UTF-8 formatting APIs on .NET, caching pre-serialized metric/name/unit/static-tag bytes, and reusing serialized tags across histogram outputs.
Adds object label-value formatting paths (common primitives + invariant-culture formatting) and corresponding unit tests.
Adds fuzz tests that compare serializer output against a reference implementation.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/PrometheusSerializerTests.cs	Adds/adjusts unit tests for object label-value formatting and invariant-culture behavior.
test/OpenTelemetry.Exporter.Prometheus.HttpListener.FuzzTests/PrometheusSerializerFuzzTests.cs	Adds fuzz coverage for object label-value serialization against a reference implementation.
src/Shared/CharExtensions.cs	Introduces a shared shim for `char.IsAscii*` APIs on non-`NET` TFMs.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/OpenTelemetry.Exporter.Prometheus.HttpListener.csproj	Links the new shared `CharExtensions` shim into the HttpListener exporter project.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusSerializerExt.cs	Refactors metric writing (notably histogram) to reuse/copy pre-serialized tag bytes and rent buffers when needed.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusSerializer.cs	Major serializer changes: UTF-8 direct formatting, escaped-string fast paths, static-tag caching, and new object label-value overload.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusMetric.cs	Caches ASCII byte representations of metric names/metadata/unit and stores serialized static tags.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusCollectionManager.cs	Expands buffer-growth exception handling to include `ArgumentException` as well as `IndexOutOfRangeException`.
src/OpenTelemetry.Exporter.Prometheus.AspNetCore/OpenTelemetry.Exporter.Prometheus.AspNetCore.csproj	Links the new shared `CharExtensions` shim into the ASP.NET Core exporter project.
src/OpenTelemetry.Api/OpenTelemetry.Api.csproj	Links the new shared `CharExtensions` shim into the API project (for `char.IsAscii*` usage).
src/OpenTelemetry.Api/Context/Propagation/TraceStateUtils.cs	Switches ASCII validation logic to `char.IsAscii*` APIs.
src/OpenTelemetry.Api/Context/Propagation/TraceContextPropagator.cs	Switches some ASCII validation logic to `char.IsAscii*` APIs.
OpenTelemetry.slnx	Adds the new shared `CharExtensions.cs` file to the solution.

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- Throw if buffer is too small. - Fix inconsistent handling of formatting and Unicode.

Update TODO comments related to JSON.

cijothomas · 2026-04-29T01:51:56Z

Prometheus.HttpListener

If this is only helpful for above, then I dont think it's worth it, given it is a non prod component. If this is in shared code and benefits aspnetcore prometheus, then definitely worth it.

martincostello · 2026-04-29T06:11:56Z

It applies to both.

paulomorgado · 2026-04-29T07:46:35Z

Prometheus.HttpListener

If this is only helpful for above, then I dont think it's worth it, given it is a non prod component. If this is in shared code and benefits aspnetcore prometheus, then definitely worth it.

@cijothomas, even if it's not supported, it's definitely used in production.

Thanks, @martincostello!

Use `Task.WaitAsync()`.

martincostello · 2026-05-09T18:26:18Z

Superseded by #7279.

[Prometheus.HttpListener] Improve performance

7cac55d

- Improve the performance of `PrometheusSerializer` for .NET 8+ by using `SearchValues<T>`. - Add fuzz tests for `PrometheusSerializer`.

github-actions Bot added the pkg:OpenTelemetry.Exporter.Prometheus.HttpListener Issues related to OpenTelemetry.Exporter.Prometheus.HttpListener NuGet package label Apr 25, 2026

martincostello added 2 commits April 25, 2026 20:54

[Prometheus.HttpListener] Fix tests

bdb4112

Handle buffer resize.

[Prometheus.HttpListener] Fix test

358e2f3

Handle different exception type between .NET and .NET Framework.

martincostello marked this pull request as ready for review April 25, 2026 20:38

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Comment thread src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusCollectionManager.cs

[Prometheus.HttpListener] Address feedback

4aecfea

Update comment.

This was referenced Apr 26, 2026

[Exporter.Prometheus] Support target info configuration #7158

Open

[Exporter.Prometheus] Support scope info configuration #7157

Open

github-actions Bot added the perf Performance related label Apr 26, 2026

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martincostello added the pkg:OpenTelemetry.Exporter.Prometheus.AspNetCore Issues related to OpenTelemetry.Exporter.Prometheus.AspNetCore NuGet package label Apr 26, 2026

[Exporter.Prometheus] Extend coverage

8609727

Add missing patch coverage.

github-actions Bot removed the pkg:OpenTelemetry.Exporter.Prometheus.AspNetCore Issues related to OpenTelemetry.Exporter.Prometheus.AspNetCore NuGet package label Apr 26, 2026

[Exporter.Prometheus] Fix lint warnings

27a1d2e

Encode the strings.

martincostello marked this pull request as draft April 26, 2026 18:31

martincostello added 2 commits April 26, 2026 19:57

[Exporter.Prometheus] Extend coverage

65d6b25

Add missing coverage for static labels.

[Exporter.Prometheus] Extend coverage

fb2545d

Add remaining (easy) coverage and remove unused code.

martincostello marked this pull request as ready for review April 26, 2026 20:30

martincostello added 2 commits April 27, 2026 09:26

Merge branch 'main' into PrometheusSerializer-perf

93d6a8a

[Exporter.Prometheus] Remove parameters

d6db630

Remove now-unused parameters from benchmarks.

martincostello mentioned this pull request Apr 27, 2026

[Exporter.Prometheus] Extend test coverage and fix surfaced issues #7179

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Merge branch 'main' into PrometheusSerializer-perf

4e86902

martincostello added 7 commits April 27, 2026 21:44

[Exporter.Prometheus] Reduce duplication

b0c53f1

Use helper for ASCII checking.

[Exporter.Prometheus] Fix-up merge

21b3a09

Fix some test changes that were removed during merge.

[Exporter.Prometheus] Fix tests

140da7a

Fix broken UTF-8 tests.

[Exporter.Prometheus] Reduce duplication

2445d2a

Factor away some duplicated code paths.

[Exporter.Prometheus] Refactoring

fbbbc06

Tidy up some of the formatting.

Merge branch 'main' into PrometheusSerializer-perf

c1124f4

[Exporter.Prometheus] Polyfill char methods

5fe7480

Add polyfills for `char`'s `IsAsciiDigit`, `IsAsciiLetterOrDigit` and `IsAsciiLetterLower` methods and remove helpers.

github-actions Bot added pkg:OpenTelemetry.Api Issues related to OpenTelemetry.Api NuGet package pkg:OpenTelemetry.Exporter.Prometheus.AspNetCore Issues related to OpenTelemetry.Exporter.Prometheus.AspNetCore NuGet package labels Apr 28, 2026

martincostello mentioned this pull request Apr 28, 2026

[Infra] Polyfill static char methods #7194

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martincostello added 2 commits April 28, 2026 21:28

[Exporter.Prometheus] Address feedback

29784ae

- Throw if buffer is too small. - Fix inconsistent handling of formatting and Unicode.

[Exporter.Prometheus] Update comments

b46cb19

Update TODO comments related to JSON.

martincostello changed the title ~~[Prometheus.HttpListener] Improve performance~~ [Exporter.Prometheus] Improve performance Apr 29, 2026

martincostello added 2 commits May 1, 2026 10:29

Merge branch 'main' into PrometheusSerializer-perf

74e5259

[Exporter.Prometheus] Simplify test

c24c7ed

Use `Task.WaitAsync()`.

github-actions Bot removed the pkg:OpenTelemetry.Api Issues related to OpenTelemetry.Api NuGet package label May 1, 2026

martincostello added the keep-open Prevents issues and pull requests being closed as stale label May 7, 2026

martincostello mentioned this pull request May 9, 2026

[Exporter.Prometheus] Improve performance #7279

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martincostello closed this May 9, 2026

martincostello deleted the PrometheusSerializer-perf branch May 9, 2026 18:26

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martincostello commented Apr 28, 2026

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Benchmark summary: `main` vs `PrometheusSerializer-perf`