The ready queue is per invoker - it has to be (and basically the current implementation; I’m not convinced you need to change that from Kafka at first: what’s the expected occupancy in the Kafka queue, per invoker, vs any other implementation you have in mind?).
The overflow queue, could be per invoker or not. Today both queues are conflated into a single topic per invoker. Hence, two queues. -r > On Oct 4, 2017, at 10:49 PM, Tyson Norris <[email protected]> wrote: > > So "dispatches immediately to an invoker" is currently implemented as a Kafka > topic-per-invoker. If we don't change that Kafka transport to something else, > I'm not sure what you have in mind to get down to "only 2 queues". In other > words the "ready queue" seems problematic to dispatch via a single queue to > multiple invokers if based on the current Kafka impl. > > >> On Oct 4, 2017, at 6:29 PM, Rodric Rabbah <[email protected]> wrote: >> >> What you’re describing is generalized to essentially two queues. The ready >> queue which dispatches immediately to an invoker with capacity and an >> overflow queue. Whether the latter is one per invoker or global may not >> matter much as long as it’s drained by the load balancer and not committed >> otherwise to the invoker ready queue where it is difficult to reassign to an >> available invoker later (ala work stealing). There are pathologies one has >> to guard against and we should consider fairness policies as well. There’s >> good theory in this space that I can imagine using to model the heuristics. >> >> -r >> >>> On Oct 4, 2017, at 8:39 PM, Tyson Norris <[email protected]> wrote: >>> >>> Not sure what you mean by two queues - you mean two queues per invoker? Or >>> total? >>> >>>> On Oct 4, 2017, at 5:14 PM, Rodric Rabbah <[email protected]> wrote: >>>> >>>> A two queue (topic) approach can mitigate the lack of random access from a >>>> Kafka topic/queue once a request is committed (in today’s architecture). >>>> This could enable work stealing in particular since the (overflow) queue >>>> can be drained upstream (ie load balancer) and reassigned to free >>>> invokers. Balancing cold start that container locality would them be a >>>> heuristic we can apply more judiciously as capacity is available (versus >>>> the current approach which binds too early and prevents rebalancing). >>>> >>>> -r >>>> >>>>> On Oct 4, 2017, at 7:45 PM, Tyson Norris <[email protected]> >>>>> wrote: >>>>> >>>>> Hi - >>>>> I’ve been discussing a bit with a few about optimizing the queueing that >>>>> goes on ahead of invokers so that things behave more simply and >>>>> predictable. >>>>> >>>>> In short: Instead of scheduling activations to an invoker on receipt, do >>>>> the following: >>>>> - execute the activation "immediately" if capacity is available >>>>> - provide a single overflow topic for activations that cannot execute >>>>> “immediately" >>>>> - schedule from the overflow topic when capacity is available >>>>> >>>>> (BTW “Immediately” means: still queued via existing invoker topics, but >>>>> ONLY gets queued there in the case that the invoker is not fully loaded, >>>>> and therefore should execute it “very soon") >>>>> >>>>> Later: it would also be good to provide more container state data from >>>>> invoker to controller, to get better scheduling options - e.g. if some >>>>> invokers can handle running more containers than other invokers, that >>>>> info can be used to avoid over/under-loading the invokers (currently we >>>>> assume each invoker can handle 16 activations, I think) >>>>> >>>>> I put a wiki page proposal here: >>>>> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcwiki.apache.org%2Fconfluence%2Fdisplay%2FOPENWHISK%2FInvoker%2BActivation%2BQueueing%2BChange&data=02%7C01%7C%7C3ff41b0527be4e13398c08d50b8614ee%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C636427592860490625&sdata=afOAkeXRW6iArXa72IGd6gnhVyrOwXsDxnjfSAQqL18%3D&reserved=0 >>>>> >>>>> WDYT? >>>>> >>>>> Thanks >>>>> Tyson
