nginx slow for no reason

[Marki555]

Thanks for your hints. Furtunately the issues disappeared. However I
would like to know how to troubleshoot it in the future.
The mentioned command produces this output (not interesting lines
filtered out):
bill3:~:# ss -nlt
Recv-Q Send-Q                                 Local Address:Port        
                          Peer Address:Port
0      128                                                *:111         
                                     *:*
0      128                                   92.240.244.176:80          
                                     *:*
0      5                                                 :::53          
                                    :::*
0      5                                                  *:53          
                                     *:*
0      1024                                       127.0.0.1:2812        
                                     *:*

What is Recv-Q/Send-Q? Is it the listen backlog queue length? How can I
see if the queue is full? On this new server I have it 128, but on old
it is 511 (for both apache and nginx). Why?
/proc/sys/net/core/netdev_max_backlog is 1000
/proc/sys/net/ipv4/tcp_max_syn_backlog is 1024

And what is the number of ESTABLISHED sockets without process
associated? Are these the connections waiting in queue to be accepted by
nginx? I have these values now (while nginx is responding within few ms
to server-status and handling about 150 conn/s):

bill3:~:# munin-run netstat_tcpstates|grep SYN_RECV
SYN_RECV.value 127
bill3:~:# netstat -ntp|grep EST|grep -- \ -|wc -l
60

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,213502,213638#msg-213638