* perf(loadbalance): fast-path zero-allocation roundRobin for homogeneous record sets
Signed-off-by: Manuel Rüger <manuel@rueg.eu>
* plugin/loadbalance: copy before shuffling in the fast path
The fast path shuffled the caller's slice in place, which is not safe.
roundRobin must not modify its input: a backend may hand back a slice it
owns rather than one built for the response. plugin/file does exactly that
- Lookup returns elem.Type(qtype), which is the zone tree's own []dns.RR -
so an in-place shuffle reorders the zone itself, visible to every other
query and racing with the ones running concurrently.
Copy the records into a fresh slice and shuffle that instead. This is still
a single allocation rather than the four slices the partitioning path builds,
so most of the gain is kept:
name old time/op new time/op delta
RoundRobin 353 ns 244 ns -31%
name old alloc/op new alloc/op delta
RoundRobin 118 B 54 B -54%
name old allocs/op new allocs/op delta
RoundRobin 5 4 -20%
Also reorder the type check so a response led by a CNAME is rejected on the
first record instead of scanning the whole answer section first.
TestRoundRobinDoesNotMutateInput pins the contract; it fails against the
in-place version.
Signed-off-by: Manuel Rüger <manuel@rueg.eu>
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Signed-off-by: Manuel Rüger <manuel@rueg.eu>
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