[Openvpn-users] Re: Performance problem

[Charles Duffy <cduffy@xxxxxxxxxxx>]

Jon Bendtsen wrote:
> on my client computer, enabling comp-lzo used alot of CPU.

That's unusual -- LZO typically can compress data at about 1/12 the 
speed of a raw memcpy() and decompress at 1/3 memcpy() speed. Unless 
you're transferring *massive* amounts of data, it shouldn't make a 
measurable impact (except inasmuch as the larger amount of throughput 
via the tun device causes increased overhead elsewhere).

> > I know how to start tcpdump, and maybe ethereal. But I don't know
> > what I'm looking for. Can you give me a hint?

See if you have patterns where large packets sent on one side show up as 
multiple smaller packets on the other, are rejected en route such that 
they need to be resent as fragments by the endpoint itself, or simply 
disappear.

OpenVPN's mtu-test will try to automatically determine what the largest 
packet size that actually goes through is; you can then use its values 
to update your config file.


That said, when you have a specific issue like this, "anything unusual" 
is a good thing to look for. Is the database client doing continuous 
communication with the server during the startup phase, or is there a 
wait state somewhere where it pauses? If you find a spot where it's 
waiting for something to happen (which isn't very unusual at all), try 
to determine exactly what that is.


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