[Opensim-dev] Does OpenSim need to leave so many packets marked as reliable?

[Sean Dague]

Justin Clark-Casey wrote:
> Hi there,
> 
> A vast number of the packets that we send out from OpenSim (usually >95% according to the statistics printed to the 
> Linden viewer log on shutdown) are marked as reliable.  This requires that the viewer respond with an ack, and it just 
> doesn't appear that this is done very well when a large number of reliables are sent.  A lot of acks never come and we 
> often appear to end up resending thousands (or in the worst case tens of thousands) of packets.
> 
> In a private experiment I've set Header.Reliable = false for the LayerDataPacket and ObjectUpdatePacket (which appear to 
> be the greatest sent by count, and which are currently reliable by default in libOMV).  Naturally, this cuts down the 
> vast number of resends (and possibly some of the packet_out_of_order messages that come out on the console log) without 
> any apparant ill effects.  However, my testing has been pretty limited so I'm minded to wait until Monday before making 
> any trunk changes, since then I can get a better load test with multiple avatars (this doesn't stop anybody else testing 
> of course :-)
> 
> Any opinions on this?  Is there a good reason for these packets to remain reliable (when resends are probably rare 
> anyway)?  libOMV appears to mark every packet as reliable by default...  and then OpenSim removes this from a couple of 
> them but not from others.

When you do the "no ill effects" test makes sure to put yourself on a
lossy network, like a slow DSL connection or a cellular modem link,
where you'll actually drop 30% of your packets.  Ter did this early on
to make sure our bw code was doing anything useful in these cases.

Testing for no ill effects on a good ethernet link is a non-test, as you
aren't actually seeing what happens if you drop packets.

	-Sean

-- 
Sean Dague / Neas Bade
sdague at gmail.com
http://dague.net


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