[Interest] It is happening again.

Bill Crocker william.crocker at analog.com
Tue Sep 22 22:09:57 CEST 2015

Fellow Qt Enthusiasts:

It is happening again.

I have a client server/app which uses Qt for the socket communication.
Occasionally it gets sick. When it is sick:

1 - It takes multiple attempts for a client to connect to the server.
     The connection attempts fail with: *ERROR*, server communication error: 
     After several attempts it works. The sicker it gets the more attempts it takes
     to connect.

2 - During these periods, the invalid SYN cookies number on the server steadily 
     >netstat -ts | grep SYN
         302658 invalid SYN cookies received    <-------
     >netstat -ts | grep SYN
         302745 invalid SYN cookies received    <-------

3 - If I restart the server process, all is well for a while.

4 - This is not something which can be reproduced on demand.

5 - The server machine is not heavily loaded during these times.
     The server image size is 275 Mb.
     It has 61 files open.
     The 1-min load average is 0.32
     The server has been running for 11 days.

The system is built with Qt-4.8.6, but I have no
evidence that this problem is related to the use of Qt.

It is running on RHEL 6.6

Any suggestions would be greatly appreciated.


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