Hi Jon and Alexis, Indeed by default the scheduler will try to make space for spare capacity in your frontend instances. There are usually two reasons for this.
The first is that requests do not usually come in regularly, they arrive in spikes and various irregular patterns. In order to comfortably handle the spikes without pending latency, an app needs more instances than would be expected by purely multiplying qps and latency. The second is that if the app were to receive more load, having spare capacity is helpful to serve the additional load without pending latency. The design of the scheduler is that the default automatic mode decides to minimize pending latency, and provide excess spare capacity, to help deal with the two issues explained above. Obviously, not all apps will want this, especially in light of the new billing formula. This is why there is now the ability to opt-out of this by using the Performance Settings options of max-idle-instances and min-pending-delay. With those options you can opt-out and signal to the scheduler that pending latency and spare capacity are not as important for your app as instance utilization. I hope that helps, Jon On Tue, Sep 6, 2011 at 1:08 AM, Alexis <alexis.hanico...@gmail.com> wrote: > Hi, > > I also have noticed something odd between QPS and latency, although my > numbers are not as bad as yours. > I generally have stats like this: > > Total number of instances Average QPS* Average Latency* > Average Memory > 210 total 0.599 252.3 ms > 72.1 MBytes > > With a latency of 0.25sec, I'd expect to have a QPS close to 4, and > hence reducing the number of instances needed. > But QPS is still very low... > > What makes QPS and Latency so different? > > > On 1 sep, 17:04, jon <jonni.g...@gmail.com> wrote: >> Hi guys, >> >> I may be missing something here but looking at the below screenshot of my >> instances, it seems like GAE is overly eager to add instances. >> >> Each instance seems to be serving a request every 8 seconds approximately, >> which feels high. Do the numbers look right to you? >> >> Thanks in advance, >> Jonni >> >> <https://lh3.googleusercontent.com/-R73wUepWYAA/Tl-eYELjwMI/AAAAAAAAAA...> > > -- > 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.
