+1 to everything Patrick said. Note that our TCP keepalive strategy on B2G at the moment is (in the absence of other network activity) to ping every 10 seconds for the 1st minute a connection is alive, and then we drop off sharply to pinging every 10 minutes. Keepalive pings are disabled for long-lived XHRs (and IIRC websockets too? Steve, do you remember?) and also IIRC HTTP/2 (since Http/2 has it's own ping).
There's an inherent latency/power-use tradeoff here. I've long wondered what the right tradeoff is for B2G (I've leaned towards stopping keepalive pings after the 1st minute, to save battery). If someone has thoughts here I'm interested to hear them. Perhaps it'll be moot if we teach apps to close connections that have been idle. Jason On Tue, Feb 3, 2015 at 7:26 AM, Patrick McManus <[email protected]> wrote: > cc: steve who did the firefox work around this. > > one of the issues you will run into is OS portability - you might very well > standardize something that's isn't portably implementable on standard > kernels. > > Using sessions on the order of 2 or 3 minutes with a tiny bit of keep-alive > seems to work pretty well, and closing them after that point. That's the > HTTP/2 strategy right now. We've looked at the distribution of timeouts in > the past - there is a notable spike around 60 seconds, but it still only > made up a small fraction of the total distribution. > > If you have some kind of nop like application layer method (such as smtp > nop :)) you can pipeline that just before your real operation and put a > timer on that response, creating a new session if it fails. This doesn't > add any latency due to the pipeline when everything is fine. That's a bit > better than open ended K-A in my opinion, particularly if you really hold > that connection open for a long duration. but some protocols (HTTP/1 e.g.) > aren't well suited to that. > > There are of course severe tradeoffs in terms of battery and network > overhead in using tcp keep-alives. Most KA transmissions are going to be > full radio wakeups. I would think that those trades would be especially > painful for Firefox OS. Legacy protocols using that api might be better off > just taking the performance hit of establishing new connections. > > > On Tue, Feb 3, 2015 at 9:15 AM, Andrew Sutherland <[email protected]> > wrote: > > > I raised an issue on the TCP and UDP socket web API spec ( > > http://www.w3.org/2012/sysapps/tcp-udp-sockets/) about exposing TCP > > keep-alive settings at > > https://github.com/sysapps/tcp-udp-sockets/issues/80. I did this > because > > for the Firefox OS Gaia email app we were seeing connections that were > > effectively dead but without reasonable TCP keepalive settings we weren't > > noticing this (and then were at the mercy of the TCP retransmit timeouts, > > presumably.) > > > > Especially since we worked around the problem in the email app thus far > by > > more aggressively closing otherwise-idle connections, I do not feel like > I > > have sufficient wisdom/experience to confidently suggest the right course > > of defaults or whether it's best to expose the raw linux TCP stack > settings > > or something else. > > > > So, if those on this list have opinions, especially those backed up by > > data, it would be great if you could chime in on > > https://github.com/sysapps/tcp-udp-sockets/issues/80. It's probably > > worth noting that from the perspective of Firefox OS, the TCP socket API > is > > a legacy API that exists to support existing pre-web technologies, but > that > > web sockets and its origin-based security model are the way forward (or > Web > > RTC's peer-to-peer mechanisms, etc.). So the API doesn't have to be > > perfect. > > > > Andrew > > _______________________________________________ > > dev-tech-network mailing list > > [email protected] > > https://lists.mozilla.org/listinfo/dev-tech-network > > > > > _______________________________________________ > dev-tech-network mailing list > [email protected] > https://lists.mozilla.org/listinfo/dev-tech-network > -- Jason _______________________________________________ dev-tech-network mailing list [email protected] https://lists.mozilla.org/listinfo/dev-tech-network
