Hey Joshua, This might be crazy, but with free apps you get 9 hours of backends per day for free as well. Could you have the kiosk hit a dynamic backend and only users go through the frontends?
Greg On Fri, Sep 2, 2011 at 12:55 PM, Joshua Smith <joshuaesm...@charter.net>wrote: > My app gets hit by a kiosk about every 3 minutes, and that chews up about > 1sec of CPU, and kicks off a task that eats another 250ms. Users come and > go now and then. Today I tried 3 different settings: > > < 9am: Max idle = 1, max latency = 1s > 9am - 1pm: Max idle = auto, max latency = 1s > 1pm - now: Max idle = 1, max latency = 5s > > > > For low-traffic, it appears that max idle = 1 is the same as "auto". That > makes sense. I'm going to leave it at auto, since I'd like to be able to > handle spikes well. > > It looks like when I set the max latency way up, it sometimes lets the > second instance die, but never for very long. > > When I've looked at the instances they never seem to have been alive all > that long. So I think the scheduler is spinning up one, adding another, > letting the first die, adding another, and so on. > > Right now I'm in one of those 1 instance troughs. The site is quite > responsive, while I poke around, and it isn't starting another instance. So > here in the trough, I'm getting the same behavior that was reported by the > person who tried a "hello world" test. Yet the above graph is what it is. > > As I'm writing this, the number of instances just jumped up to 2! So now I > can see what caused it: > > The kiosk hits the URL with an XMLHttp request to make sure it's alive, and > if that works OK, then it refreshes itself. This bit of nastiness is there > because it's impossible to get a browser to handle failed page loads 100% > consistently well. > > When the kiosk hits the URL, a task is launched to do some background > processing recording that the heartbeat happened. The two hits therefore > lead to two tasks. I'm using countdown = 1. > > These two tasks are bunching up in the queue, and being processed > essentially at the same time. That requires, you guessed it, two instances! > > I have been thinking of task queues as sort of a background process, and I > certainly wouldn't expect the system to spin up an instance just to handle a > queued task. But that thinking isn't really right, since the docs > explicitly suggest that spawning a lot of tasks is a good way to get a bunch > of instances to munch your hard problem in parallel. > > So my fix is actually not so hard. I just need to pass a param with the > "just checking" initial kiosk request and use that to avoid spawning the > task. That way I'll get hit-hit-task, not hit-hit-task-task, and presumably > the system won't feel compelling to crank up a new instance. > > If we get two kiosks going and they happen to get synchronized (as such > things tend to do), then I'll be screwed. But for now, I think I've got my > fix... > > If you're still reading, I'll give you a reward: If you are trying to > diagnose why you have 2 instances when you have the sliders set to 1/15, go > to your log, view with Info and find the requests that are spinning up a new > instance. Now look at all requests and find that one that spun up the evil > second instance. Was it right on the heels of another request? I bet it > was. Is it your fault? (In my case, it certainly was my fault.) > Regardless, if you want to avoid that second instance, you need to find a > way to get those requests to be farther apart. > > -Joshua > > -- > You received this message because you are subscribed to the Google Groups > "Google App Engine" group. > To post to this group, send email to google-appengine@googlegroups.com. > To unsubscribe from this group, send email to > google-appengine+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/google-appengine?hl=en. > -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
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