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

[chris fedde]

Having read through this thread I begin to wonder if it is a DNS
issue.  mysql may be looking for and failing to find reverse dns
entries.  The characteristic for this particular problem is a 90
second delay from the tcp connection till the response banner.

You can check to see if this is the issue using tcpdump.

On Sun, Nov 8, 2009 at 9:17 PM, Jim Ockers <ockers at ockers.net> wrote:
> 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
>
>
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