Apache delays response 30 sec (keep-alive expires)

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Hi,

I use apache 2.2.17 with tomcat 6.0.29 connected via mod_jk 1.2.31.

 

At one customer (only in one system and it was not re-produced elsewhere) I have the following issue:

 

1) client sends request to apache HTTP/1.1
2) apache forwards to tomcat
3) tomcat sends response to apache
4) apache sends some packets back
5) there is a 30 seconds delay before last packets are send followed by a FIN packet from apache.

 

30 seconds is a keep-alive timeout in apache. So I assume that keep-alive somehow flushes the buffers so the response is finally send. There is no traffic on that connection for 30 seconds only the clients ACKs all data send till then.

 

From the tcpdump I see nothing wrong in the AJP communication, e.g. it is properly ended. So  if there is a bug in the mod_jk or apache it looks to be quite specific.

 

Also we had something similar cca 1,5 years ago with apache 2.2.8, where we got it working by changing from chunked encoding to content length in response (so I assume the size of the packet maybe plays a role somewhere).

 

Now it is also not working with content-length, when compared the old packets the only small visible diff was that in one case the tcp segment size was 1448 (because tcp timestamps were used) and in the not working  case it was 1460, but I would assume to see some error in tcpdump if that would be a network issue.

 

Any idea what this could be? I could send tcpdump with the error case (not sure how big attachments can be send per email).

 

Thanks,
Tomas.

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