Aias00 opened a new issue, #6571:
URL: https://github.com/apache/shenyu/issues/6571
## Description
`doSelect` allocates a fresh `ConcurrentSkipListMap` and, for every upstream
x 5 virtual nodes, calls `hash("SHENYU-" + upstream.getUrl() + "-HASH-" + i)`
which does `MessageDigest.getInstance("MD5")` (JCA lookup + new instance),
`key.getBytes(UTF_8)`, and `md5.digest()` (new `byte[]`). The ring is never
cached; it is fully rebuilt on every selection even though the upstream set
only changes on health-check/admin events.
## Location
```
shenyu-loadbalancer/.../spi/HashLoadBalancer.java:44-56 (doSelect), 58-77
(hash)
```
## Impact
Per hash-LB request: 1 SkipListMap + 5*N MD5 instances + 5*N String
concatenations + 5*N `byte[]` digests. For N=10 upstreams that's 50 MD5
hashes/request. Very high CPU + allocation on the sticky/consistent-hash path;
scales linearly with RPS and upstream count.
## Suggested fix
Build and cache the ring (e.g. `ConcurrentHashMap<String,
TreeMap<Long,Upstream>>` keyed by selectorId, invalidated when
`UpstreamCacheManager.submit`/health-check mutates the list). Use a
`ThreadLocal<MessageDigest>` or a faster non-crypto hash (murmur3/xxHash).
Precompute virtual-node keys when the upstream list changes.
## Related existing issue(s)
None
_Identified during the 2026-08-02 audit; full list in
[`docs/issue-candidates-2026-08-02.md`](docs/issue-candidates-2026-08-02.md)._
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