Question about bind-dlz performance limit

[WXR]

I'm using bind-dlz(bind version 9.10) with mysql to store zone data.
According to‍ the dlz official documents I use the compile arguments " -enable-threads=no‍".

Now I use dnstop and netstat to monitor the performance,and find there is a perfomance bottleneck of bind-dlz.

Once the QPS increses to 500-600,the response time of each dns query will be very large , up to 600msec-1000msec.And the Recv-Q‍ of udp socket where reach 124928.‍(the default /proc/sys/net/core/rmem_default‍ value)

# dnstop eth1 -R -Q
‍Queries: 519 new, 9326898 
Replies: 508 new, 6612496 total‍

# watch -n 1 netstat -lnp
 Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name       
udp     124813‍      0 121.199.47.200:53           0.0.0.0:*                               31867/named ‍

I think 500-600 QPS is too low,is it the normal performance of bind-dlz?How to optimize it?
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