On 18 October 2013 07:47, Kirk Pepperdine <kirk.pepperd...@gmail.com> wrote: > Hi Sebb, > > In my testing, the option off creating threads on demand instead of all at > once has made a huge difference in my being able to control rate of arrivals > on the server. It has convinced me that simply using the throughput > controller isn't enough and that the threading model in JMeter *must* change. > It is the threading model that is the biggest source of CO in JMeter. > Unfortunately we weren't able to come to some way of a non-disruptive change > in JMeter to make this happen. > > The model I was proposing would have JMeter generate an event heap sorted by > the time when a sampler should be fired. A thread pool should be used to eat > off of the heap and fire the events as per scheduled. This would allow JMeter > to break the inappropriate relationship of a thread being a user. The > solution is not perfect in that you will still have to fight with thread > schedulers and hypervisors to get things to happen on queue. However, I > believe the end result will be a far more scalable product that will require > far fewer threads to produce far higher loads on the server. > > As for your idea on the using the throughput controller. IHMO triggering an > assert only worsens the CO problem. In fact, if the response times from the > timeouts are not added into the results, in other words they are omitted from > the data set, you've only made the problem worse as you are filter out bad > data points from the result sets making the results better than they should > be. Peter Lawyer's (included here for the purpose of this discussion) > technique for correcting CO is to simply recognize when the event should have > been triggered and then start the timer for that event at that time. So the > latency reported will include the time before event triggering. > > Gil Tene's done some work with JMeter. I'll leave it up to him to post what > he's done. The interesting bit that he's created is HrdHistogram > (https://github.com/giltene/HdrHistogram). It is not only a better way to > report results,it offers techniques to calculate and correct for CO. Also Gil > might be able to point you to a more recent version of his on CO talk. It > might be nice to have a new sampler that incorporates this work. > > On a side note, I've got a Servlet filter that is JMX component that measures > a bunch of stats from the servers POV. It's something that could be > contributed as it could be used to help understand the source of CO.. if not > just complement JMeter's view of latency. >
I think you have missed the point of my posting. The idea was to detect when CO has happened, and use that information to change the test setup. In some cases it may not be possible avoid the CO, but in other cases, it should be possible to reduce the transaction rate in each thread such that long sample times don't cause the next sample to be delayed. And at least the user will have the required information. So, I'll ask again: is my proposal for *detecting* CO reasonable? If not, what changes are needed? Changing JMeter to behave differently is a matter for a separate thread. > Regards, > Kirk > > > On 2013-10-18, at 12:27 AM, sebb <seb...@gmail.com> wrote: > >> It looks to be quite difficult to avoid the issue of Coordination >> Omission without a major redesign of JMeter. >> >> However, it may be a lot easier to detect when the condition has occurred. >> This would potentially allow the test settings to be changed to reduce >> or eliminate the occurrences - e.g. by increasing the number of >> threads or spreading the load across more JMeter instances. >> >> The Constant Throughput Controller calculates the desired wait time, >> and if this is less than zero - i.e. a sample should already have been >> generated - it could trigger the creation of a failed Assertion >> showing the time difference. >> >> Would this be sufficient to detect all CO occurrences? >> If not, what other metric needs to be checked? >> >> Even if it is not the only possible cause, would it be useful as a >> starting point? >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: user-unsubscr...@jmeter.apache.org >> For additional commands, e-mail: user-h...@jmeter.apache.org >> > --------------------------------------------------------------------- To unsubscribe, e-mail: user-unsubscr...@jmeter.apache.org For additional commands, e-mail: user-h...@jmeter.apache.org
