filterHealthy() allocated 2 slices (available + backups) per call.
filterHealthyAndExclude() allocated 3 (adds excludeSet map).
IPHash allocated fnv.New64a() object per call.
All triggered on every request's LB selection.
Changes:
- Add filterContext struct holding reusable buffers, managed by sync.Pool
- Replace filterHealthy → filterInto (writes into pooled buffers)
- Replace filterHealthyAndExclude → filterIntoExcluding (pooled buffers)
- Add inline fnvHash64a() to avoid fnv.New64a() heap allocation
- Update all 6 balancer algorithms (RoundRobin, WeightedRoundRobin,
LeastConnections, IPHash, Random, ConsistentHash) to use pooled
filterContext via acquire/release pattern
- ConsistentHash.SelectExcludingByKey also uses pool for targetSet
- Remove buildExcludeSet (merged into filterIntoExcluding)
Result: allocs/op reduced from 2-3 to 0-1 on all LB Select paths.
Target 新增 MaxConns/MaxFails/FailTimeout/Backup/Down/ProxyURI 字段，
实现 IsAvailable/RecordFailure/RecordSuccess 软失败机制，
filterHealthy 支持备份服务器优先级选择，
新增 random（Power of Two Choices）负载均衡算法。
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
