[clue-tech] MySQL server reply packets delayed/lost under network congestion?

[Jim Ockers]

Hi Dave,

David L. Anselmi wrote:
> Jim Ockers wrote:
>> Whenever there is sustained high bandwidth network traffic over the 
>> PPP link (such as downloading a large e-mail attachment, or streaming 
>> video) the mysql connections all start to time out because response 
>> packets from the server are not received at the client.  I observed 
>> this by doing a simple "telnet server 3306" and observed that the 
>> MySQL banner response with version number was delayed by several 
>> seconds or until the bandwidth-hogging stopped.
>>
>> What I don't understand is why I can still transfer data from other 
>> servers on the Linux system, such as "net view \\server" and "dir 
>> \\server\sharename" (using the Windows redirector to talk to Samba on 
>> the Linux system).  Also the apache web server on the Linux system 
>> responds normally, both from a web browser and also in response to 
>> "telnet server 80" and then "GET / HTTP/1.0".
>
> I assume that other services are delayed like the MySQL banner.  Most 
> of what you tried though would use fairly small responses (one packet, 
> even?) so maybe the MySQL protocol is more verbose.
>
No, actually the only service that is delayed is MySQL response packets 
including the banner.  Apache responds right away to a GET / HTTP/1.0 
request, samba responds right away to a Windows redirector request, FTP 
responds right away, and so forth.  MySQL is the only one that seems to 
take an unreasonably long time to respond when there is something 
hogging the bandwidth.
> It seems that clients have several timeouts available:
>
> http://dev.mysql.com/doc/refman/5.1/en/mysql-options.html
>
> Maybe the protocol takes too long in some cases.
I'm not too sure about that, but since the banner is delayed I wonder if 
MySQL has some sort of built-in congestion management or something.

Thanks though,
Jim