Don't get me wrong Gwen :) I'm definitely for removing as less burden as possible from users. All I'm saying it is not straight-forward to do so, and we'd better at least have a concrete implementation design on the KIP page rather than just a one-line change of the config semantics.
On Sun, Jun 5, 2016 at 1:09 PM, Gwen Shapira <g...@confluent.io> wrote: > If it is hard for you, just imagine how much fun the users will have. > > Machines have X GB available RAM. Someone has to figure out how to > divide it for processors and rocksDB. The user doesn't have any > special knowledge that you don't in this case, so there's no point in > pushing the decision to the user - he won't be able to make a better > decision. > > Gwen > > On Sun, Jun 5, 2016 at 10:44 PM, Guozhang Wang <wangg...@gmail.com> wrote: > > There are some details needed to be figured out if we go global: > > > > A KafkaStreams instance could have M threads, and each thread could > various > > number (let's say N, but in practice it may be different from thread to > > thread) tasks, and each task contains a sub-topology with P caches (again > > in practice it may be different depending on which sub-topology it > > contains). > > > > Say if user specified X Gb for this KafkaStreams instance, then each > cache > > will get X / M / N / P Gb. But remember N and P can change from rebalance > > to rebalance, and threads does not communicate with each other during > their > > life time. So it is hard to determine M and N dynamically. > > > > Plus, different caches may have different cache hit rate, so distributing > > the memory evenly to them may not be an optimal solution (some caches may > > be flushed much more frequently than others), and also since we are > > considering to use instrumentation.getObjectSize which is approximate, it > > may exaggerate the imbalance. > > > > > > Guozhang > > > > > > On Sat, Jun 4, 2016 at 11:54 PM, Eno Thereska <eno.there...@gmail.com> > > wrote: > > > >> Hi Jay, > >> > >> We can make it global instead of per-processor, sounds good. > >> > >> Thanks > >> Eno > >> > >> > >> > On 3 Jun 2016, at 23:15, Jay Kreps <j...@confluent.io> wrote: > >> > > >> > Hey Eno, > >> > > >> > Should the config be the global memory use rather than the > per-processor? > >> > That is, let’s say I know I have fixed a 1GB heap because that is > what I > >> > set for Java, and want to use 100MB for caching, it seems like right > now > >> > I’d have to do some math that depends on my knowing a bit about how > >> caching > >> > works to figure out how to set that parameter so I don't run out of > >> memory. > >> > Does it also depend on the number of partitions assigned (and hence > the > >> > number of task), if so that makes it even harder to set since each > time > >> > rebalancing happens that changes so it is then pretty hard to set > safely. > >> > > >> > You could theoretically argue for either bottom up (you know how much > >> cache > >> > you need per processor as you have it and you want to get exactly > that) > >> or > >> > top down (you know how much memory you have to spare but can't be > >> bothered > >> > to work out what that amounts to per-processor). I think our > experience > >> has > >> > been that 99% of people never change the default and if it runs out of > >> > memory they really struggle to fix it and kind of blame us, so I think > >> top > >> > down and a global config might be better. :-) > >> > > >> > Example: https://issues.apache.org/jira/browse/KAFKA-3775 > >> > > >> > -Jay > >> > > >> > On Fri, Jun 3, 2016 at 2:39 PM, Eno Thereska <eno.there...@gmail.com> > >> wrote: > >> > > >> >> Hi Gwen, > >> >> > >> >> Yes. As an example, if cache.max.bytes.buffering set to X, and if > users > >> >> have A aggregation operators and T KTable.to() operators, then X*(A > + T) > >> >> total bytes will be allocated for caching. > >> >> > >> >> Eno > >> >> > >> >>> On 3 Jun 2016, at 21:37, Gwen Shapira <g...@confluent.io> wrote: > >> >>> > >> >>> Just to clarify: "cache.max.bytes.buffering" is per processor? > >> >>> > >> >>> > >> >>> On Thu, Jun 2, 2016 at 11:30 AM, Eno Thereska < > eno.there...@gmail.com> > >> >> wrote: > >> >>>> Hi there, > >> >>>> > >> >>>> I have created KIP-63: Unify store and downstream caching in > streams > >> >>>> > >> >> > >> > https://cwiki.apache.org/confluence/display/KAFKA/KIP-63%3A+Unify+store+and+downstream+caching+in+streams > >> >> < > >> >> > >> > https://cwiki.apache.org/confluence/display/KAFKA/KIP-63:+Unify+store+and+downstream+caching+in+streams > >> >>> > >> >>>> > >> >>>> > >> >>>> Feedback is appreciated. > >> >>>> > >> >>>> Thank you > >> >>>> Eno > >> >> > >> >> > >> > >> > > > > > > -- > > -- Guozhang > -- -- Guozhang
