nginx slow for no reason

Marki555 nginx-forum at
Wed Aug 10 15:02:16 UTC 2011

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                                   
0      5                                                 :::53          
0      5                                                  *:53          
0      1024                                     

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

Posted at Nginx Forum:,213502,213638#msg-213638

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