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 > >> > > >> > > > > >
