Umut Polat b1a7fc8db1 fix(cache): prefer positive cache over SERVFAIL in ncache (#8003) ...

When serve_stale is enabled, a cached SERVFAIL in ncache shadows a valid
positive entry in pcache because ncache is always checked first. SERVFAIL
is transient and should not mask a known-good answer.

When the ncache hit is a SERVFAIL, check pcache for a valid entry before
returning the SERVFAIL. NXDOMAIN and NODATA are unaffected and still
follow the existing ncache-first lookup per RFC 2308.

Fixes #7956

Signed-off-by: umut-polat <52835619+umut-polat@users.noreply.github.com>

2026-05-19 20:28:35 -07:00

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