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plugin/cache: remove superfluous allocations in item.toMsg (#7700)

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This commit removes superfluous allocations of the Answer, Ns, and Extra
slices when copying a cached a dns.Msg. The allocations are superfluous
because we immediately overwrite the newly copied slices with
filterRRSlice. It also updates filterRRSlice to pre-calculate the size
of the slice being copied into.

Benchmark results:

goos: darwin
goarch: arm64
pkg: github.com/coredns/coredns/plugin/cache
cpu: Apple M4 Pro
                 │ base.10.txt │             new.10.txt             │
                 │   sec/op    │   sec/op     vs base               │
CacheResponse-14   471.1n ± 0%   462.9n ± 2%  -1.74% (p=0.009 n=10)

                 │ base.10.txt │            new.10.txt             │
                 │    B/op     │    B/op     vs base               │
CacheResponse-14    672.0 ± 0%   656.0 ± 0%  -2.38% (p=0.000 n=10)

                 │ base.10.txt │            new.10.txt             │
                 │  allocs/op  │ allocs/op   vs base               │
CacheResponse-14    13.00 ± 0%   12.00 ± 0%  -7.69% (p=0.000 n=10)

Signed-off-by: Charlie Vieth <charlie.vieth@gmail.com>
This commit is contained in:
Charlie Vieth
2025-11-21 18:07:59 -05:00
committed by GitHub
parent 854048b0ab
commit de010910e2
3 changed files with 18 additions and 7 deletions
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10
plugin/cache/dnssec.go vendored
View File

@@ -6,8 +6,14 @@ import "github.com/miekg/dns"
// If dup is true the RRs in rrs are _copied_ before adjusting their
// TTL and the slice of copied RRs is returned.
func filterRRSlice(rrs []dns.RR, ttl uint32, dup bool) []dns.RR {
n := 0
for _, r := range rrs {
if r.Header().Rrtype != dns.TypeOPT {
n++
}
}
rs := make([]dns.RR, n)
j := 0
rs := make([]dns.RR, len(rrs))
for _, r := range rrs {
if r.Header().Rrtype == dns.TypeOPT {
continue
@@ -20,5 +26,5 @@ func filterRRSlice(rrs []dns.RR, ttl uint32, dup bool) []dns.RR {
rs[j].Header().Ttl = ttl
j++
}
return rs[:j]
return rs
}