Historical record. Measurements and status refer to the original report date. Read the English original at revision 61e75e9.

Parser-backed lossless mutations: overlay baseline vs result

Recorded 2026-07-20 on darwin/arm64, Apple M1 Max, Go 1.26.5. Both sides use BenchmarkParserBackedOverlayComparison, the same 10,000-file fixtures, 256-byte staged payload, Go toolchain, hardware, -benchtime=3x, and -count=3. The table reports the median ns/op; allocation columns are the stable values reported by all three samples.

The baseline is commit 43f7214 (mutable), before the parser-backed mutation implementation. The comparison benchmark is self-contained and was copied unchanged into an archive of that commit:

mkdir /private/tmp/okf-parser-backed-baseline
git archive 43f7214 | tar -x -C /private/tmp/okf-parser-backed-baseline
cp mutation/overlay_comparison_benchmark_test.go \
  /private/tmp/okf-parser-backed-baseline/mutation/overlay_comparison_benchmark_test.go

(cd /private/tmp/okf-parser-backed-baseline && \
  GOCACHE=/private/tmp/okf-go-cache-baseline \
  go test ./mutation -run '^$' \
    -bench '^BenchmarkParserBackedOverlayComparison$' \
    -benchtime=3x -benchmem -count=3)

GOCACHE=/private/tmp/okf-go-cache-result \
go test ./mutation -run '^$' \
  -bench '^BenchmarkParserBackedOverlayComparison$' \
  -benchtime=3x -benchmem -count=3

Fixture	Baseline ns/op	Result ns/op	Baseline B/op	Result B/op	Baseline allocs/op	Result allocs/op
clone changed 10,000	1,379,528	489,667	3,347,232	1,049,456	10,036	37
repeated Paths, base 10,000	3,001,708	1,467,111	764,581	600,704	35	34
rename staged 10,000	1,253,625	467,014	3,349,077	1,049,701	10,044	38

The clone and staged-rename allocation reduction is the expected consequence of sharing private immutable payload bytes while preserving defensive public reads. The repeated-Paths result includes the public result copy on both sides; the result tree reuses its successfully enumerated and normalized base-path cache.