Hi Dong, Yes, there is a sensor in the patch about the split occurrence.
Currently it is a count instead of rate. In practice, it seems count is easier to use in this case. But I am open to change. Thanks, Jiangjie (Becket) Qin On Fri, Mar 3, 2017 at 7:43 PM, Dong Lin <lindon...@gmail.com> wrote: > Hey Becket, > > I haven't looked at the patch yet. But since we are going to try the > split-on-oversize solution, should the KIP also add a sensor that shows the > rate of split per second and the probability of split? > > Thanks, > Dong > > > On Fri, Mar 3, 2017 at 6:39 PM, Becket Qin <becket....@gmail.com> wrote: > > > Just to clarify, the implementation is basically what I mentioned above > > (split/resend + adjusted estimation evolving algorithm) and changing the > > compression ratio estimation to be per topic. > > > > Thanks, > > > > Jiangjie (Becket) Qin > > > > On Fri, Mar 3, 2017 at 6:36 PM, Becket Qin <becket....@gmail.com> wrote: > > > > > I went ahead and have a patch submitted here: > > > https://github.com/apache/kafka/pull/2638 > > > > > > Per Joel's suggestion, I changed the compression ratio to be per topic > as > > > well. It seems working well. Since there is an important behavior > change > > > and a new sensor is added, I'll keep the KIP and update it according. > > > > > > Thanks, > > > > > > Jiangjie (Becket) Qin > > > > > > On Mon, Feb 27, 2017 at 3:50 PM, Joel Koshy <jjkosh...@gmail.com> > wrote: > > > > > >> > > > >> > Lets say we sent the batch over the wire and received a > > >> > RecordTooLargeException, how do we split it as once we add the > message > > >> to > > >> > the batch we loose the message level granularity. We will have to > > >> > decompress, do deep iteration and split and again compress. right? > > This > > >> > looks like a performance bottle neck in case of multi topic > producers > > >> like > > >> > mirror maker. > > >> > > > >> > > >> Yes, but these should be outliers if we do estimation on a per-topic > > basis > > >> and if we target a conservative-enough compression ratio. The producer > > >> should also avoid sending over the wire if it can be made aware of the > > >> max-message size limit on the broker, and split if it determines that > a > > >> record exceeds the broker's config. Ideally this should be part of > topic > > >> metadata but is not - so it could be off a periodic describe-configs > > >> <https://cwiki.apache.org/confluence/display/KAFKA/KIP-4+-+ > > >> Command+line+and+centralized+administrative+operations#KIP- > > >> 4-Commandlineandcentralizedadministrativeoperations-Describe > > >> ConfigsRequest> > > >> (which isn't available yet). This doesn't remove the need to split and > > >> recompress though. > > >> > > >> > > >> > On Mon, Feb 27, 2017 at 10:51 AM, Becket Qin <becket....@gmail.com> > > >> wrote: > > >> > > > >> > > Hey Mayuresh, > > >> > > > > >> > > 1) The batch would be split when an RecordTooLargeException is > > >> received. > > >> > > 2) Not lower the actual compression ratio, but lower the estimated > > >> > > compression ratio "according to" the Actual Compression > Ratio(ACR). > > >> > > > > >> > > An example, let's start with Estimated Compression Ratio (ECR) = > > 1.0. > > >> Say > > >> > > the compression ratio of ACR is ~0.8, instead of letting the ECR > > >> dropped > > >> > to > > >> > > 0.8 very quickly, we only drop 0.001 every time when ACR < ECR. > > >> However, > > >> > > once we see an ACR > ECR, we increment ECR by 0.05. If a > > >> > > RecordTooLargeException is received, we reset the ECR back to 1.0 > > and > > >> > split > > >> > > the batch. > > >> > > > > >> > > Thanks, > > >> > > > > >> > > Jiangjie (Becket) Qin > > >> > > > > >> > > > > >> > > > > >> > > On Mon, Feb 27, 2017 at 10:30 AM, Mayuresh Gharat < > > >> > > gharatmayures...@gmail.com> wrote: > > >> > > > > >> > > > Hi Becket, > > >> > > > > > >> > > > Seems like an interesting idea. > > >> > > > I had couple of questions : > > >> > > > 1) How do we decide when the batch should be split? > > >> > > > 2) What do you mean by slowly lowering the "actual" compression > > >> ratio? > > >> > > > An example would really help here. > > >> > > > > > >> > > > Thanks, > > >> > > > > > >> > > > Mayuresh > > >> > > > > > >> > > > On Fri, Feb 24, 2017 at 3:17 PM, Becket Qin < > becket....@gmail.com > > > > > >> > > wrote: > > >> > > > > > >> > > > > Hi Jay, > > >> > > > > > > >> > > > > Yeah, I got your point. > > >> > > > > > > >> > > > > I think there might be a solution which do not require adding > a > > >> new > > >> > > > > configuration. We can start from a very conservative > compression > > >> > ratio > > >> > > > say > > >> > > > > 1.0 and lower it very slowly according to the actual > compression > > >> > ratio > > >> > > > > until we hit a point that we have to split a batch. At that > > >> point, we > > >> > > > > exponentially back off on the compression ratio. The idea is > > >> somewhat > > >> > > > like > > >> > > > > TCP. This should help avoid frequent split. > > >> > > > > > > >> > > > > The upper bound of the batch size is also a little awkward > today > > >> > > because > > >> > > > we > > >> > > > > say the batch size is based on compressed size, but users > cannot > > >> set > > >> > it > > >> > > > to > > >> > > > > the max message size because that will result in oversized > > >> messages. > > >> > > With > > >> > > > > this change we will be able to allow the users to set the > > message > > >> > size > > >> > > to > > >> > > > > close to max message size. > > >> > > > > > > >> > > > > However the downside is that there could be latency spikes in > > the > > >> > > system > > >> > > > in > > >> > > > > this case due to the splitting, especially when there are many > > >> > messages > > >> > > > > need to be split at the same time. That could potentially be > an > > >> issue > > >> > > for > > >> > > > > some users. > > >> > > > > > > >> > > > > What do you think about this approach? > > >> > > > > > > >> > > > > Thanks, > > >> > > > > > > >> > > > > Jiangjie (Becket) Qin > > >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > On Thu, Feb 23, 2017 at 1:31 PM, Jay Kreps <j...@confluent.io> > > >> wrote: > > >> > > > > > > >> > > > > > Hey Becket, > > >> > > > > > > > >> > > > > > Yeah that makes sense. > > >> > > > > > > > >> > > > > > I agree that you'd really have to both fix the estimation > > (i.e. > > >> > make > > >> > > it > > >> > > > > per > > >> > > > > > topic or make it better estimate the high percentiles) AND > > have > > >> the > > >> > > > > > recovery mechanism. If you are underestimating often and > then > > >> > paying > > >> > > a > > >> > > > > high > > >> > > > > > recovery price that won't fly. > > >> > > > > > > > >> > > > > > I think you take my main point though, which is just that I > > >> hate to > > >> > > > > exposes > > >> > > > > > these super low level options to users because it is so hard > > to > > >> > > explain > > >> > > > > to > > >> > > > > > people what it means and how they should set it. So if it is > > >> > possible > > >> > > > to > > >> > > > > > make either some combination of better estimation and > > splitting > > >> or > > >> > > > better > > >> > > > > > tolerance of overage that would be preferrable. > > >> > > > > > > > >> > > > > > -Jay > > >> > > > > > > > >> > > > > > On Thu, Feb 23, 2017 at 11:51 AM, Becket Qin < > > >> becket....@gmail.com > > >> > > > > >> > > > > wrote: > > >> > > > > > > > >> > > > > > > @Dong, > > >> > > > > > > > > >> > > > > > > Thanks for the comments. The default behavior of the > > producer > > >> > won't > > >> > > > > > change. > > >> > > > > > > If the users want to use the uncompressed message size, > they > > >> > > probably > > >> > > > > > will > > >> > > > > > > also bump up the batch size to somewhere close to the max > > >> message > > >> > > > size. > > >> > > > > > > This would be in the document. BTW the default batch size > is > > >> 16K > > >> > > > which > > >> > > > > is > > >> > > > > > > pretty small. > > >> > > > > > > > > >> > > > > > > @Jay, > > >> > > > > > > > > >> > > > > > > Yeah, we actually had debated quite a bit internally what > is > > >> the > > >> > > best > > >> > > > > > > solution to this. > > >> > > > > > > > > >> > > > > > > I completely agree it is a bug. In practice we usually > leave > > >> some > > >> > > > > > headroom > > >> > > > > > > to allow the compressed size to grow a little if the the > > >> original > > >> > > > > > messages > > >> > > > > > > are not compressible, for example, 1000 KB instead of > > exactly > > >> 1 > > >> > MB. > > >> > > > It > > >> > > > > is > > >> > > > > > > likely safe enough. > > >> > > > > > > > > >> > > > > > > The major concern for the rejected alternative is > > >> performance. It > > >> > > > > largely > > >> > > > > > > depends on how frequent we need to split a batch, i.e. how > > >> likely > > >> > > the > > >> > > > > > > estimation can go off. If we only need to the split work > > >> > > > occasionally, > > >> > > > > > the > > >> > > > > > > cost would be amortized so we don't need to worry about it > > too > > >> > > much. > > >> > > > > > > However, it looks that for a producer with shared topics, > > the > > >> > > > > estimation > > >> > > > > > is > > >> > > > > > > always off. As an example, consider two topics, one with > > >> > > compression > > >> > > > > > ratio > > >> > > > > > > 0.6 the other 0.2, assuming exactly same traffic, the > > average > > >> > > > > compression > > >> > > > > > > ratio would be roughly 0.4, which is not right for either > of > > >> the > > >> > > > > topics. > > >> > > > > > So > > >> > > > > > > almost half of the batches (of the topics with 0.6 > > compression > > >> > > ratio) > > >> > > > > > will > > >> > > > > > > end up larger than the configured batch size. When it > comes > > to > > >> > more > > >> > > > > > topics > > >> > > > > > > such as mirror maker, this becomes more unpredictable. To > > >> avoid > > >> > > > > frequent > > >> > > > > > > rejection / split of the batches, we need to configured > the > > >> batch > > >> > > > size > > >> > > > > > > pretty conservatively. This could actually hurt the > > >> performance > > >> > > > because > > >> > > > > > we > > >> > > > > > > are shoehorn the messages that are highly compressible to > a > > >> small > > >> > > > batch > > >> > > > > > so > > >> > > > > > > that the other topics that are not that compressible will > > not > > >> > > become > > >> > > > > too > > >> > > > > > > large with the same batch size. At LinkedIn, our batch > size > > is > > >> > > > > configured > > >> > > > > > > to 64 KB because of this. I think we may actually have > > better > > >> > > > batching > > >> > > > > if > > >> > > > > > > we just use the uncompressed message size and 800 KB batch > > >> size. > > >> > > > > > > > > >> > > > > > > We did not think about loosening the message size > > restriction, > > >> > but > > >> > > > that > > >> > > > > > > sounds a viable solution given that the consumer now can > > fetch > > >> > > > > oversized > > >> > > > > > > messages. One concern would be that on the broker side > > >> oversized > > >> > > > > messages > > >> > > > > > > will bring more memory pressure. With KIP-92, we may > > mitigate > > >> > that, > > >> > > > but > > >> > > > > > the > > >> > > > > > > memory allocation for large messages may not be very GC > > >> > friendly. I > > >> > > > > need > > >> > > > > > to > > >> > > > > > > think about this a little more. > > >> > > > > > > > > >> > > > > > > Thanks, > > >> > > > > > > > > >> > > > > > > Jiangjie (Becket) Qin > > >> > > > > > > > > >> > > > > > > > > >> > > > > > > On Wed, Feb 22, 2017 at 8:57 PM, Jay Kreps < > > j...@confluent.io> > > >> > > wrote: > > >> > > > > > > > > >> > > > > > > > Hey Becket, > > >> > > > > > > > > > >> > > > > > > > I get the problem we want to solve with this, but I > don't > > >> think > > >> > > > this > > >> > > > > is > > >> > > > > > > > something that makes sense as a user controlled knob > that > > >> > > everyone > > >> > > > > > > sending > > >> > > > > > > > data to kafka has to think about. It is basically a bug, > > >> right? > > >> > > > > > > > > > >> > > > > > > > First, as a technical question is it true that using the > > >> > > > uncompressed > > >> > > > > > > size > > >> > > > > > > > for batching actually guarantees that you observe the > > >> limit? I > > >> > > > think > > >> > > > > > that > > >> > > > > > > > implies that compression always makes the messages > > smaller, > > >> > > which i > > >> > > > > > think > > >> > > > > > > > usually true but is not guaranteed, right? e.g. if > someone > > >> > > encrypts > > >> > > > > > their > > >> > > > > > > > data which tends to randomize it and then enables > > >> > compressesion, > > >> > > it > > >> > > > > > could > > >> > > > > > > > slightly get bigger? > > >> > > > > > > > > > >> > > > > > > > I also wonder if the rejected alternatives you describe > > >> > couldn't > > >> > > be > > >> > > > > > made > > >> > > > > > > to > > >> > > > > > > > work: basically try to be a bit better at estimation and > > >> > recover > > >> > > > when > > >> > > > > > we > > >> > > > > > > > guess wrong. I don't think the memory usage should be a > > >> > problem: > > >> > > > > isn't > > >> > > > > > it > > >> > > > > > > > the same memory usage the consumer of that topic would > > need? > > >> > And > > >> > > > > can't > > >> > > > > > > you > > >> > > > > > > > do the splitting and recompression in a streaming > fashion? > > >> If > > >> > we > > >> > > an > > >> > > > > > make > > >> > > > > > > > the estimation rate low and the recovery cost is just > ~2x > > >> the > > >> > > > normal > > >> > > > > > cost > > >> > > > > > > > for that batch that should be totally fine, right? (It's > > >> > > > technically > > >> > > > > > true > > >> > > > > > > > you might have to split more than once, but since you > > halve > > >> it > > >> > > each > > >> > > > > > time > > >> > > > > > > I > > >> > > > > > > > think should you get a number of halvings that is > > >> logarithmic > > >> > in > > >> > > > the > > >> > > > > > miss > > >> > > > > > > > size, which, with better estimation you'd hope would be > > >> super > > >> > > duper > > >> > > > > > > small). > > >> > > > > > > > > > >> > > > > > > > Alternatively maybe we could work on the other side of > the > > >> > > problem > > >> > > > > and > > >> > > > > > > try > > >> > > > > > > > to make it so that a small miss on message size isn't a > > big > > >> > > > problem. > > >> > > > > I > > >> > > > > > > > think original issue was that max size and fetch size > were > > >> > > tightly > > >> > > > > > > coupled > > >> > > > > > > > and the way memory in the consumer worked you really > > wanted > > >> > fetch > > >> > > > > size > > >> > > > > > to > > >> > > > > > > > be as small as possible because you'd use that much > memory > > >> per > > >> > > > > fetched > > >> > > > > > > > partition and the consumer would get stuck if its fetch > > size > > >> > > wasn't > > >> > > > > big > > >> > > > > > > > enough. I think we made some progress on that issue and > > >> maybe > > >> > > more > > >> > > > > > could > > >> > > > > > > be > > >> > > > > > > > done there so that a small bit of fuzziness around the > > size > > >> > would > > >> > > > not > > >> > > > > > be > > >> > > > > > > an > > >> > > > > > > > issue? > > >> > > > > > > > > > >> > > > > > > > -Jay > > >> > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > > >> > > > > > > > On Tue, Feb 21, 2017 at 12:30 PM, Becket Qin < > > >> > > becket....@gmail.com > > >> > > > > > > >> > > > > > > wrote: > > >> > > > > > > > > > >> > > > > > > > > Hi folks, > > >> > > > > > > > > > > >> > > > > > > > > I would like to start the discussion thread on > KIP-126. > > >> The > > >> > KIP > > >> > > > > > propose > > >> > > > > > > > > adding a new configuration to KafkaProducer to allow > > >> batching > > >> > > > based > > >> > > > > > on > > >> > > > > > > > > uncompressed message size. > > >> > > > > > > > > > > >> > > > > > > > > Comments are welcome. > > >> > > > > > > > > > > >> > > > > > > > > The KIP wiki is following: > > >> > > > > > > > > https://cwiki.apache.org/ > confluence/display/KAFKA/KIP- > > >> > > > > > > > > 126+-+Allow+KafkaProducer+to+b > > >> atch+based+on+uncompressed+siz > > >> > e > > >> > > > > > > > > > > >> > > > > > > > > Thanks, > > >> > > > > > > > > > > >> > > > > > > > > Jiangjie (Becket) Qin > > >> > > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > >> > > > > > > >> > > > > > >> > > > > > >> > > > > > >> > > > -- > > >> > > > -Regards, > > >> > > > Mayuresh R. Gharat > > >> > > > (862) 250-7125 > > >> > > > > > >> > > > > >> > > > >> > > > >> > > > >> > -- > > >> > -Regards, > > >> > Mayuresh R. Gharat > > >> > (862) 250-7125 > > >> > > > >> > > > > > > > > >
