[SDK] Compact metric storage after stream removal

[matt-hensley]

Changes

Removed metric streams leave empty slots in the reader's storage that the collect path keeps scanning. Collection slows as metric streams churn.

Storage is now compacted during collection, so only active streams are scanned.

Results (same session, same machine; churned vs. clean provider, ratio = churned / clean):

.NET 10.0

Historical streams	Temporality	Before: clean	Before: churned	Before: ratio	After: clean	After: churned	After: ratio
16	Cumulative	225.1 ns	231.3 ns	1.03	224.8 ns	226.9 ns	1.01
16	Delta	186.6 ns	187.1 ns	1.00	182.6 ns	180.9 ns	0.99
256	Cumulative	224.5 ns	344.5 ns	1.53	222.3 ns	226.6 ns	1.02
256	Delta	179.4 ns	292.8 ns	1.63	179.2 ns	183.0 ns	1.02
1024	Cumulative	234.8 ns	699.5 ns	2.98	228.0 ns	233.1 ns	1.02
1024	Delta	176.8 ns	654.2 ns	3.70	182.3 ns	178.4 ns	0.98

.NET Framework 4.7.2

Historical streams	Temporality	Before: clean	Before: churned	Before: ratio	After: clean	After: churned	After: ratio
16	Cumulative	646.7 ns	660.3 ns	1.02	615.0 ns	631.3 ns	1.03
16	Delta	527.8 ns	527.6 ns	1.00	570.2 ns	504.7 ns	0.89 *
256	Cumulative	616.0 ns	1,128.8 ns	1.83	614.2 ns	622.7 ns	1.01
256	Delta	527.2 ns	1,009.8 ns	1.92	516.2 ns	516.6 ns	1.00
1024	Cumulative	630.9 ns	2,752.2 ns	4.36	614.4 ns	624.1 ns	1.02
1024	Delta	505.2 ns	2,371.8 ns	4.70	498.1 ns	511.9 ns	1.03

** benchmark noise

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, successful build/tests, etc.)
• Tests added/updated
• CHANGELOG.md file(s) updated for non-trivial changes
• Changes in public API reviewed (if applicable)
• AI usage disclosure:
  • No AI used
  • AI-assisted
  • Bulk AI-generated
• I have the experience and knowledge necessary to understand, review, and validate all content in this PR¹

Footnotes

1. Yes, I can answer maintainer questions about the content of this PR without using AI. ↩

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Merged · refreshed 2026-10-15 07:57 UTC

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.28%. Comparing base (e5b5ac6) to head (a21a021).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7945      +/-   ##
==========================================
- Coverage   92.28%   92.28%   -0.01%     
==========================================
  Files         363      363              
  Lines       21022    21038      +16     
==========================================
+ Hits        19401    19414      +13     
- Misses       1621     1624       +3     

Flag	Coverage Δ
unittests-Project-Experimental	92.40% <100.00%> (-0.01%)	⬇️
unittests-Project-Stable	92.40% <100.00%> (-0.01%)	⬇️

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

Files with missing lines	Coverage Δ
...rc/OpenTelemetry/Metrics/Reader/MetricReaderExt.cs	93.90% <100.00%> (+0.65%)	⬆️

... and 2 files with indirect coverage changes