Hi Jun, 10. My understanding is that MemoryRecords would under the covers be allocated in chunks, so logically it still would be one MemoryRecords object, it's just instead of allocating one large chunk upfront, smaller chunks are allocated as needed to grow the batch and linked into a list.
11. The reason for 2 sizes is to avoid change of behavior when triggering batch send with large linger.ms. Currently, a batch send is triggered once the batch reaches 16KB by default, if we just raise the default to 256KB, then the batch send will be delayed. Using a separate value would allow keeping the current behavior when sending the batch out, but provide better throughput with high latency + high bandwidth channels. -Artem On Tue, Dec 7, 2021 at 5:29 PM Jun Rao <j...@confluent.io.invalid> wrote: > Hi, Luke, > > Thanks for the KIP. A few comments below. > > 10. Accumulating small batches could improve memory usage. Will that > introduce extra copying when generating a produce request? Currently, a > produce request takes a single MemoryRecords per partition. > 11. Do we need to introduce a new config batch.max.size? Could we just > increase the default of batch.size? We probably need to have KIP-794 > < > https://cwiki.apache.org/confluence/display/KAFKA/KIP-794%3A+Strictly+Uniform+Sticky+Partitioner > > > resolved > before increasing the default batch size since the larger the batch size, > the worse the problem in KIP-794. > 12. As for max.request.size, currently it's used for both the max record > size and the max request size, which is unintuitive. Perhaps we could > introduce a new config max.record.size that defaults to 1MB. We could then > increase max.request.size to sth like 10MB. > > Thanks, > > Jun > > > On Mon, Nov 29, 2021 at 6:02 PM Artem Livshits > <alivsh...@confluent.io.invalid> wrote: > > > Hi Luke, > > > > I don't mind increasing the max.request.size to a higher number, e.g. 2MB > > could be good. I think we should also run some benchmarks to see the > > effects of different sizes. > > > > I agree that changing round robin to random solves an independent > existing > > issue, however the logic in this KIP exacerbates the issue, so there is > > some dependency. > > > > -Artem > > > > On Wed, Nov 24, 2021 at 12:43 AM Luke Chen <show...@gmail.com> wrote: > > > > > Hi Artem, > > > Yes, I agree if we go with random selection instead of round-robin > > > selection, the latency issue will be more fair. That is, if there are > 10 > > > partitions, the 10th partition will always be the last choice in each > > round > > > in current design, but with random selection, the chance to be selected > > is > > > more fair. > > > > > > However, I think that's kind of out of scope with this KIP. This is an > > > existing issue, and it might need further discussion to decide if this > > > change is necessary. > > > > > > I agree the default 32KB for "batch.max.size" might be not huge > > improvement > > > compared with 256KB. I'm thinking, maybe default to "64KB" for > > > "batch.max.size", and make the documentation clear that if the > > > "batch.max.size" > > > is increased, there might be chances that the "ready" partitions need > to > > > wait for next request to send to broker, because of the > > "max.request.size" > > > (default 1MB) limitation. "max.request.size" can also be considered to > > > increase to avoid this issue. What do you think? > > > > > > Thank you. > > > Luke > > > > > > On Wed, Nov 24, 2021 at 2:26 AM Artem Livshits > > > <alivsh...@confluent.io.invalid> wrote: > > > > > > > > maybe I can firstly decrease the "batch.max.size" to 32KB > > > > > > > > I think 32KB is too small. With 5 in-flight and 100ms latency we can > > > > produce 1.6MB/s per partition. With 256KB we can produce 12.8MB/s > per > > > > partition. We should probably set up some testing and see if 256KB > has > > > > problems. > > > > > > > > To illustrate latency dynamics, let's consider a simplified model: 1 > > > > in-flight request per broker, produce latency 125ms, 256KB max > request > > > > size, 16 partitions assigned to the same broker, every second 128KB > is > > > > produced to each partition (total production rate is 2MB/sec). > > > > > > > > If the batch size is 16KB, then the pattern would be the following: > > > > > > > > 0ms - produce 128KB into each partition > > > > 0ms - take 16KB from each partition send (total 256KB) > > > > 125ms - complete first 16KB from each partition, send next 16KB > > > > 250ms - complete second 16KB, send next 16KB > > > > ... > > > > 1000ms - complete 8th 16KB from each partition > > > > > > > > from this model it's easy to see that there are 256KB that are sent > > > > immediately, 256KB that are sent in 125ms, ... 256KB that are sent in > > > > 875ms. > > > > > > > > If the batch size is 256KB, then the pattern would be the following: > > > > > > > > 0ms - produce 128KB into each partition > > > > 0ms - take 128KB each from first 2 partitions and send (total 256KB) > > > > 125ms - complete 2 first partitions, send data from next 2 partitions > > > > ... > > > > 1000ms - complete last 2 partitions > > > > > > > > even though the pattern is different, there are still 256KB that are > > sent > > > > immediately, 256KB that are sent in 125ms, ... 256KB that are sent in > > > > 875ms. > > > > > > > > Now, in this example if we do strictly round-robin (current > > > implementation) > > > > and we have this exact pattern (not sure how often such regular > pattern > > > > would happen in practice -- I would expect that it would be a bit > more > > > > random), some partitions would experience higher latency than others > > (not > > > > sure how much it would matter in practice -- in the end of the day > some > > > > bytes produced to a topic would have higher latency and some bytes > > would > > > > have lower latency). This pattern is easily fixed by choosing the > next > > > > partition randomly instead of using round-robin. > > > > > > > > -Artem > > > > > > > > On Tue, Nov 23, 2021 at 12:08 AM Luke Chen <show...@gmail.com> > wrote: > > > > > > > > > Hi Tom, > > > > > Thanks for your comments. And thanks for Artem's explanation. > > > > > Below is my response: > > > > > > > > > > > Currently because buffers are allocated using batch.size it means > > we > > > > can > > > > > handle records that are that large (e.g. one big record per batch). > > > > Doesn't > > > > > the introduction of smaller buffer sizes (batch.initial.size) mean > a > > > > > corresponding decrease in the maximum record size that the producer > > can > > > > > handle? > > > > > > > > > > Actually, the "batch.size" is only like a threshold to decide if > the > > > > batch > > > > > is "ready to be sent". That is, even if you set the > "batch.size=16KB" > > > > > (default value), users can still send one record sized with 20KB, > as > > > long > > > > > as the size is less than "max.request.size" in producer (default > > 1MB). > > > > > Therefore, the introduction of "batch.initial.size" won't decrease > > the > > > > > maximum record size that the producer can handle. > > > > > > > > > > > But isn't there the risk that drainBatchesForOneNode would end up > > not > > > > > sending ready > > > > > batches well past when they ought to be sent (according to their > > > > linger.ms > > > > > ), > > > > > because it's sending buffers for earlier partitions too > aggressively? > > > > > > > > > > Did you mean that we have a "max.request.size" per request (default > > is > > > > > 1MB), and before this KIP, the request can include 64 batches in > > single > > > > > request ["batch.size"(16KB) * 64 = 1MB], but now, we might be able > to > > > > > include 32 batches or less, because we aggressively sent more > records > > > in > > > > > one batch, is that what you meant? That's a really good point that > > I've > > > > > never thought about. I think your suggestion to go through other > > > > partitions > > > > > that just fit "batch.size", or expire "linger.ms" first, before > > > handling > > > > > the one that is > "batch.size" limit is not a good way, because it > > > might > > > > > cause the one with size > "batch.size" always in the lowest > priority, > > > and > > > > > cause starving issue that the batch won't have chance to get sent. > > > > > > > > > > I don't have better solution for it, but maybe I can firstly > decrease > > > the > > > > > "batch.max.size" to 32KB, instead of aggressively 256KB in the KIP. > > > That > > > > > should alleviate the problem. And still improve the throughput. > What > > do > > > > you > > > > > think? > > > > > > > > > > Thank you. > > > > > Luke > > > > > > > > > > On Tue, Nov 23, 2021 at 9:04 AM Artem Livshits > > > > > <alivsh...@confluent.io.invalid> wrote: > > > > > > > > > > > > I think this KIP would change the behaviour of producers when > > there > > > > are > > > > > > multiple partitions ready to be sent > > > > > > > > > > > > This is correct, the pattern changes and becomes more > > coarse-grained. > > > > > But > > > > > > I don't think it changes fairness over the long run. I think > it's > > a > > > > good > > > > > > idea to change drainIndex to be random rather than round robin to > > > avoid > > > > > > forming patterns where some partitions would consistently get > > higher > > > > > > latencies than others because they wait longer for their turn. > > > > > > > > > > > > If we really wanted to preserve the exact patterns, we could > either > > > try > > > > > to > > > > > > support multiple 16KB batches from one partition per request > > > (probably > > > > > > would require protocol change to change logic on the broker for > > > > duplicate > > > > > > detection) or try to re-batch 16KB batches from accumulator into > > > larger > > > > > > batches during send (additional computations) or try to consider > > all > > > > > > partitions assigned to a broker to check if a new batch needs to > be > > > > > created > > > > > > (i.e. compare cumulative batch size from all partitions assigned > > to a > > > > > > broker and create new batch when cumulative size is 1MB, more > > > complex). > > > > > > > > > > > > Overall, it seems like just increasing the max batch size is a > > > simpler > > > > > > solution and it does favor larger batch sizes, which is > beneficial > > > not > > > > > just > > > > > > for production. > > > > > > > > > > > > > ready batches well past when they ought to be sent (according > to > > > > their > > > > > > linger.ms) > > > > > > > > > > > > The trigger for marking batches ready to be sent isn't changed - > a > > > > batch > > > > > is > > > > > > ready to be sent once it reaches 16KB, so by the time larger > > batches > > > > > start > > > > > > forming, linger.ms wouldn't matter much because the batching > goal > > is > > > > met > > > > > > and the batch can be sent immediately. Larger batches start > > forming > > > > once > > > > > > the client starts waiting for the server, in which case some data > > > will > > > > > wait > > > > > > its turn to be sent. This will happen for some data regardless > of > > > how > > > > we > > > > > > pick data to send, the question is just whether we'd have some > > > > scenarios > > > > > > where some partitions would consistently experience higher > latency > > > than > > > > > > others. I think picking drainIndex randomly would prevent such > > > > > scenarios. > > > > > > > > > > > > -Artem > > > > > > > > > > > > On Mon, Nov 22, 2021 at 2:28 AM Tom Bentley <tbent...@redhat.com > > > > > > wrote: > > > > > > > > > > > > > Hi Luke, > > > > > > > > > > > > > > Thanks for the KIP! > > > > > > > > > > > > > > Currently because buffers are allocated using batch.size it > means > > > we > > > > > can > > > > > > > handle records that are that large (e.g. one big record per > > batch). > > > > > > Doesn't > > > > > > > the introduction of smaller buffer sizes (batch.initial.size) > > mean > > > a > > > > > > > corresponding decrease in the maximum record size that the > > producer > > > > can > > > > > > > handle? That might not be a problem if the user knows their > > maximum > > > > > > record > > > > > > > size and has tuned batch.initial.size accordingly, but if the > > > default > > > > > for > > > > > > > batch.initial.size < batch.size it could cause regressions for > > > > existing > > > > > > > users with a large record size, I think. It should be enough > for > > > > > > > batch.initial.size to default to batch.size, allowing users who > > > care > > > > > > about > > > > > > > the memory saving in the off-peak throughput case to do the > > tuning, > > > > but > > > > > > not > > > > > > > causing a regression for existing users. > > > > > > > > > > > > > > I think this KIP would change the behaviour of producers when > > there > > > > are > > > > > > > multiple partitions ready to be sent: By sending all the ready > > > > buffers > > > > > > > (which may now be > batch.size) for the first partition, we > could > > > end > > > > > up > > > > > > > excluding ready buffers for other partitions from the current > > send. > > > > In > > > > > > > other words, as I understand the KIP currently, there's a > change > > in > > > > > > > fairness. I think the code in > > > > RecordAccumulator#drainBatchesForOneNode > > > > > > will > > > > > > > ensure fairness in the long run, because the drainIndex will > > ensure > > > > > that > > > > > > > those other partitions each get their turn at being the first. > > But > > > > > isn't > > > > > > > there the risk that drainBatchesForOneNode would end up not > > sending > > > > > ready > > > > > > > batches well past when they ought to be sent (according to > their > > > > > > linger.ms > > > > > > > ), > > > > > > > because it's sending buffers for earlier partitions too > > > aggressively? > > > > > Or, > > > > > > > to put it another way, perhaps the RecordAccumulator should > > > > round-robin > > > > > > the > > > > > > > ready buffers for _all_ the partitions before trying to fill > the > > > > > > remaining > > > > > > > space with the extra buffers (beyond the batch.size limit) for > > the > > > > > first > > > > > > > partitions? > > > > > > > > > > > > > > Kind regards, > > > > > > > > > > > > > > Tom > > > > > > > > > > > > > > On Wed, Oct 20, 2021 at 1:35 PM Luke Chen <show...@gmail.com> > > > wrote: > > > > > > > > > > > > > > > Hi Ismael and all devs, > > > > > > > > Is there any comments/suggestions to this KIP? > > > > > > > > If no, I'm going to update the KIP based on my previous mail, > > and > > > > > > start a > > > > > > > > vote tomorrow or next week. > > > > > > > > > > > > > > > > Thank you. > > > > > > > > Luke > > > > > > > > > > > > > > > > On Mon, Oct 18, 2021 at 2:40 PM Luke Chen <show...@gmail.com > > > > > > wrote: > > > > > > > > > > > > > > > > > Hi Ismael, > > > > > > > > > Thanks for your comments. > > > > > > > > > > > > > > > > > > 1. Why do we have to reallocate the buffer? We can keep a > > list > > > of > > > > > > > buffers > > > > > > > > > instead and avoid reallocation. > > > > > > > > > -> Do you mean we allocate multiple buffers with > > > > > > "buffer.initial.size", > > > > > > > > > and link them together (with linked list)? > > > > > > > > > ex: > > > > > > > > > a. We allocate 4KB initial buffer > > > > > > > > > | 4KB | > > > > > > > > > > > > > > > > > > b. when new records reached and the remaining buffer is not > > > > enough > > > > > > for > > > > > > > > the > > > > > > > > > records, we create another batch with "batch.initial.size" > > > buffer > > > > > > > > > ex: we already have 3KB of data in the 1st buffer, and here > > > comes > > > > > the > > > > > > > 2KB > > > > > > > > > record > > > > > > > > > > > > > > > > > > | 4KB (1KB remaining) | > > > > > > > > > now, record: 2KB coming > > > > > > > > > We fill the 1st 1KB into 1st buffer, and create new buffer, > > and > > > > > > linked > > > > > > > > > together, and fill the rest of data into it > > > > > > > > > | 4KB (full) | ---> | 4KB (3KB remaining) | > > > > > > > > > > > > > > > > > > Is that what you mean? > > > > > > > > > If so, I think I like this idea! > > > > > > > > > If not, please explain more detail about it. > > > > > > > > > Thank you. > > > > > > > > > > > > > > > > > > 2. I think we should also consider tweaking the semantics > of > > > > > > batch.size > > > > > > > > so > > > > > > > > > that the sent batches can be larger if the batch is not > ready > > > to > > > > be > > > > > > > sent > > > > > > > > > (while still respecting max.request.size and perhaps a new > > > > > > > > max.batch.size). > > > > > > > > > > > > > > > > > > --> In the KIP, I was trying to make the "batch.size" as > the > > > > upper > > > > > > > bound > > > > > > > > > of the batch size, and introduce a "batch.initial.size" as > > > > initial > > > > > > > batch > > > > > > > > > size. > > > > > > > > > So are you saying that we can let "batch.size" as initial > > batch > > > > > size > > > > > > > and > > > > > > > > > introduce a "max.batch.size" as upper bound value? > > > > > > > > > That's a good suggestion, but that would change the > semantics > > > of > > > > > > > > > "batch.size", which might surprise some users. I think my > > > > original > > > > > > > > proposal > > > > > > > > > ("batch.initial.size") is safer for users. What do you > think? > > > > > > > > > > > > > > > > > > Thank you. > > > > > > > > > Luke > > > > > > > > > > > > > > > > > > > > > > > > > > > On Mon, Oct 18, 2021 at 3:12 AM Ismael Juma < > > ism...@juma.me.uk > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > >> I think we should also consider tweaking the semantics of > > > > > batch.size > > > > > > > so > > > > > > > > >> that the sent batches can be larger if the batch is not > > ready > > > to > > > > > be > > > > > > > sent > > > > > > > > >> (while still respecting max.request.size and perhaps a new > > > > > > > > >> max.batch.size). > > > > > > > > >> > > > > > > > > >> Ismael > > > > > > > > >> > > > > > > > > >> On Sun, Oct 17, 2021, 12:08 PM Ismael Juma < > > ism...@juma.me.uk > > > > > > > > > > wrote: > > > > > > > > >> > > > > > > > > >> > Hi Luke, > > > > > > > > >> > > > > > > > > > >> > Thanks for the KIP. Why do we have to reallocate the > > buffer? > > > > We > > > > > > can > > > > > > > > >> keep a > > > > > > > > >> > list of buffers instead and avoid reallocation. > > > > > > > > >> > > > > > > > > > >> > Ismael > > > > > > > > >> > > > > > > > > > >> > On Sun, Oct 17, 2021, 2:02 AM Luke Chen < > > show...@gmail.com> > > > > > > wrote: > > > > > > > > >> > > > > > > > > > >> >> Hi Kafka dev, > > > > > > > > >> >> I'd like to start the discussion for the proposal: > > KIP-782: > > > > > > > > Expandable > > > > > > > > >> >> batch size in producer. > > > > > > > > >> >> > > > > > > > > >> >> The main purpose for this KIP is to have better memory > > > usage > > > > in > > > > > > > > >> producer, > > > > > > > > >> >> and also save users from the dilemma while setting the > > > batch > > > > > size > > > > > > > > >> >> configuration. After this KIP, users can set a higher > > > > > batch.size > > > > > > > > >> without > > > > > > > > >> >> worries, and of course, with an appropriate > > > > > "batch.initial.size" > > > > > > > and > > > > > > > > >> >> "batch.reallocation.factor". > > > > > > > > >> >> > > > > > > > > >> >> Derailed description can be found here: > > > > > > > > >> >> > > > > > > > > >> >> > > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-782%3A+Expandable+batch+size+in+producer > > > > > > > > >> >> > > > > > > > > >> >> Any comments and feedback are welcome. > > > > > > > > >> >> > > > > > > > > >> >> Thank you. > > > > > > > > >> >> Luke > > > > > > > > >> >> > > > > > > > > >> > > > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
