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

[David L. Anselmi]

Jim Ockers wrote:
> Hi everyone,
> 
> Replying to my own post. :)  We figured it out.  MySQL tries to set the 
> IP TOS to a nonzero value.
[...]
> 1. Does anyone know how to make MySQL not do that, either a config file 
> option or command line option?
> 2. Is there some really excellent reason why MySQL would do that?

This could be a kernel bug.  Can you talk to the MySQL people who might 
know which kernel people to talk to?

By any chance are you doing any queue management that might either be 
buggy or not behave the way you think it should when presented with 
these packets?

> 3. Is there any other way (iptables mangle, for example) that we could 
> fix this packet's TOS _BEFORE_ it hits the network 
> stack/queues/buffers?  We tried with iptables mangle/OUTPUT and it was 
> too late in the network processing to have any effect on the packet.

I don't remember the tables well enough.  But you could probably do 
something creative to send the MySQL traffic through a virtual interface 
that routes to the PPP interface.  Then OUTPUT would be early enough, right?

Dave