Pre-merge immutable tag sources to reduce span creation overhead#11118
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Pre-merge immutable tag sources to reduce span creation overhead#11118
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…creation buildSpanContext() called setAllTags() 5 times per span, with two of those sources (mergedTracerTags, localRootSpanTags) being immutable across all spans. Every span redundantly re-merged them plus ran a per-span removeTag(Tags.VERSION). This change pre-merges those frozen tag sources into a preMergedRootSpanBase template at ConfigSnapshot creation time and initializes each span's TagMap via copy from the template. Root spans go from 5 setAllTags + removeTag to 3 setAllTags; child spans go from 2 effective setAllTags to 1. tag: no release note tag: ai generated Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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After running a before / after comparison, this change yields negligible real gains. |
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Summary
mergedTracerTags + localRootSpanTagsinto a frozenpreMergedRootSpanBasetemplate atConfigSnapshotcreation time (once at init / remote config update, not per-span)TagMapviatagBase.copy()from the template instead ofTagMap.create()+ 5 separatesetAllTags()callssetAllTags+removeTag(VERSION)reduced to 3setAllTagssetAllTagsreduced to 1Tags.VERSIONat merge time instead of per-spanTagMergeBenchmarkJMH benchmarkMotivation:
CoreTracer.buildSpanContext()consumed ~7% of foreground CPU in a 16-thread span creation stress test (6% in buildSpanContext itself + 1% inBucketGroup._cloneEntries). Two of the fivesetAllTags()calls used frozen/immutable tag maps that never change between spans — redundantly re-merged on every span.Benchmark results (8 threads, throughput)
TagMergeBenchmark:
CoreTracerBenchmark (end-to-end):
Test plan
*CoreTracer*tests pass (52/52)*DDSpanContext*tests pass*DDSpan*,*SpanTag*,*TagInterceptor*,*DynamicConfig*tests pass🤖 Generated with Claude Code