Razvan Dimescu 5c5b7dbf58 feat: SRTT-based nameserver selection for recursive resolver ...

BIND-style Smoothed RTT (EWMA) tracking per NS IP address. The resolver
learns which nameservers respond fastest and prefers them, eliminating
cascading timeouts from slow/unreachable IPv6 servers.

- New src/srtt.rs: SrttCache with record_rtt, record_failure, sort_by_rtt
- EWMA formula: new = (old * 7 + sample) / 8, 5s failure penalty, 5min decay
- TCP penalty (+100ms) lets SRTT naturally deprioritize IPv6-over-TCP
- Enabled flag embedded in SrttCache (no-op when disabled)
- Batch eviction (64 entries) for O(1) amortized writes at capacity
- Configurable via [upstream] srtt = true/false (default: true)
- Benchmark script: scripts/benchmark.sh (full, cold, warm, compare-all)
- Benchmarks show 12x avg improvement, 0% queries >1s (was 58%)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

2026-03-28 22:40:47 +02:00

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