[go] uuid: use bytes.Compare in UUID.Compare
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Damien Neil (Gerrit)
Oct 21, 2026, 6:55:29 PM (20 hours ago) Oct 21
to karamaru, goph...@pubsubhelper.golang.org, golang-...@googlegroups.com, golang...@luci-project-accounts.iam.gserviceaccount.com, Emmanuel Odeke, David Chase, Neal Patel, golang-co...@googlegroups.com
Damien Neil submitted the change![]( "Open in Gerrit")
Change information
Commit message:
uuid: use bytes.Compare in UUID.Compare
UUID.Compare compared the UUIDs one byte at a time, so its cost grew
with the length of the common prefix. bytes.Compare produces the same
lexicographic (RFC 9562 Section 6.11) ordering and, on arm64, compares
the 16 bytes as two 64-bit words, taking roughly constant time.
UUIDv7 values begin with a big-endian millisecond timestamp, so UUIDs
generated close in time share long prefixes, which is the common case
when sorting them or using them as keys in ordered maps.
Benchmark:
func BenchmarkCompare(b *testing.B) {
u := uuid.MustParse("01a148bf-a08a-75a1-8422-c1a47b40eec7")
for _, bc := range []struct {
name string
diffIndex int // index of the differing byte, or -1 if equal
}{
{"Equal", -1},
{"Diff0", 0},
{"Diff1", 1},
{"Diff2", 2},
{"Diff3", 3},
{"Diff7", 7},
{"Diff15", 15},
} {
v := u
if bc.diffIndex >= 0 {
v[bc.diffIndex]++
}
b.Run(bc.name, func(b *testing.B) {
b.ReportAllocs()
for b.Loop() {
u.Compare(v)
}
})
}
}
goos: darwin
goarch: arm64
pkg: uuid
cpu: Apple M4 Max
│ old │ new │
│ sec/op │ sec/op vs base │
Compare/Equal-16 10.680n ± 9% 1.864n ± 0% -82.55% (p=0.000 n=20)
Compare/Diff0-16 1.788n ± 1% 1.865n ± 0% +4.25% (p=0.000 n=20)
Compare/Diff1-16 1.810n ± 1% 1.864n ± 0% +2.98% (p=0.000 n=20)
Compare/Diff2-16 2.488n ± 4% 1.867n ± 0% -24.94% (p=0.000 n=20)
Compare/Diff3-16 3.395n ± 5% 1.864n ± 0% -45.09% (p=0.000 n=20)
Compare/Diff7-16 5.888n ± 7% 1.869n ± 1% -68.27% (p=0.000 n=20)
Compare/Diff15-16 11.070n ± 8% 1.875n ± 0% -83.07% (p=0.000 n=20)
geomean 4.087n 1.867n -54.32%
│ old │ new │
│ B/op │ B/op vs base │
Compare/Equal-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
Compare/Diff0-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
Compare/Diff1-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
Compare/Diff2-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
Compare/Diff3-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
Compare/Diff7-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
Compare/Diff15-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
geomean ² +0.00% ²
¹ all samples are equal
² summaries must be >0 to compute geomean
│ old │ new │
│ allocs/op │ allocs/op vs base │
Compare/Equal-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
Compare/Diff0-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
Compare/Diff1-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
Compare/Diff2-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
Compare/Diff3-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
Compare/Diff7-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
Compare/Diff15-16 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=20) ¹
geomean ² +0.00% ²
¹ all samples are equal
² summaries must be >0 to compute geomean
Fixes #82288
Change-Id: Id320302f0d49906af7e23b8ec8a03c2c1a4d01c2
Reviewed-on: https://go-review.googlesource.com/c/go/+/850265
Reviewed-by: Emmanuel Odeke <emma...@orijtech.com>
Auto-Submit: Emmanuel Odeke <emma...@orijtech.com>
Reviewed-by: Damien Neil <dn...@google.com>
Reviewed-by: David Chase <drc...@google.com>
LUCI-TryBot-Result: golang...@luci-project-accounts.iam.gserviceaccount.com <golang...@luci-project-accounts.iam.gserviceaccount.com>
Files:
- M src/uuid/uuid.go
Change size: XS
Delta: 1 file changed, 1 insertion(+), 7 deletions(-)
Branch: refs/heads/master
Submit Requirements:
Code-Review: +1 by Emmanuel Odeke, +2 by David Chase, +2 by Damien Neil
Review-Enforcement: Code-Review+1 by Emmanuel Odeke, Code-Review+2 by David Chase, Code-Review+2 by Damien Neil
TryBots-Pass: LUCI-TryBot-Result+1 by golang...@luci-project-accounts.iam.gserviceaccount.com
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