Low performance with UNIX SOCKET Backend

[luuvanloia4]

I created a test Remote Backend for PDNS Authoritative using UNIX SOCKET connection.
My BE received request and return response immediately without do any logic (latency = 0).
But when i do performance test with this BE via PDNS Authoritative, it''s max only 2,5k req/s.

I'm using PDNS Authoritative version 4.7 and there are my configs:

launch=remote
remote-connection-string=unix:path=/usr/local/pdns-remote-backend/run/pdns-remote-backend.socket,timeout=2000

guardian=yes

# Threads
receiver-threads=4
distributor-threads=4

# Log
log-dns-details=yes
# log-dns-queries=yes
log-timestamp=yes
loglevel=3
# loglevel=7

# cache-ttl=20
cache-ttl=0

# negquery-cache-ttl=60
negquery-cache-ttl=0

# query-cache-ttl=20
query-cache-ttl=0

zone-cache-refresh-interval=0