Charlie Vieth de010910e2 plugin/cache: remove superfluous allocations in item.toMsg (#7700) ...

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>

2025-11-21 15:07:59 -08:00

608 B

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