[Samba] samba4 ldap high load and port queue overflow

[Yuriy Tabolin]

Hi all.
I have samba 4.2.3 on freebsd 10.1 server. There are three DC and about 
350 PC on domain. DCs have 3 CPU and 3GB RAM. Some servers with services 
like apache, exim, dovecot, etc use samba4 ldap (port 389) for user 
authentication. Some times ago after adding some services to use ldap I 
found, that samba4 cannot serve all ldap requests. Every 10-30 minutes I 
see in DCs logs:
dc1 kernel: sonewconn: pcb 0xfffff800753d6ab8: Listen queue overflow: 16 
already in queue awaiting acceptance (28 occurrences)

After that I have used tcpdump for recording ldap-traffic and have seen 
that after TCP handshaking, server some times suddenly send TCP-RST to 
close connection. I have enlarged DCs resources (CPU and RAM),  
kern.ipc.somaxconn, did some other system tuning but all that didn't 
help. Load average on DCs permanently near 0.9-1.0 and samba cannot 
serve all ldap conncetions. ldap clients works well because they use as 
minimum as two domain controllers as ldap servers. Is there a some 
performance problem in samba4, slow processing ldap requests or 
something else?
Thanks for any help.

-- 
With best regards,

Tabolin Yuriy
System administrator
Speech Technology Center