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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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4
plugin/cache/item.go vendored
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@@ -82,10 +82,6 @@ func (i *item) toMsg(m *dns.Msg, now time.Time, do bool, ad bool) *dns.Msg {
m1.RecursionAvailable = i.RecursionAvailable
m1.Rcode = i.Rcode
m1.Answer = make([]dns.RR, len(i.Answer))
m1.Ns = make([]dns.RR, len(i.Ns))
m1.Extra = make([]dns.RR, len(i.Extra))
ttl := uint32(i.ttl(now))
m1.Answer = filterRRSlice(i.Answer, ttl, true)
m1.Ns = filterRRSlice(i.Ns, ttl, true)