The current configs are hard to use for the Kafka user and a little inflexible
so I am pleased to see the discussion.
Ultimately we want flexibility. We don't want to force users to understand the
underlying implementation/protocol and we want the producer to handle high or
low throughput efficiently - with the right amount of inflight data for the
conditions.
Given each producer by default has limited inflight requests per connection
then we need extra flexibility in the batch sizing.
The way I would like to be able to approach as a user is that 1) I use
linger.ms to bound my client-side produce latency 2) I use request.size and
max.inflight.requests.per.connection to calculate my upper-bound inflight data.
As a user, I don't have to think about anything else (no edge cases or
caveats). The producer handles the batching intelligently, trying to fully
utilise the request sizes while respecting the linger.
I understand Jun's point about increasing the default batch size. The only
downside I see is having to juggle the request vs batch size to avoid delaying
batches because we can only fit so many big batches in a request. That is a
calculation we force on the user and reduces flexibility.
As I understand the proposed change, each ProducerBatch would be physically
made up of a list of ByteBuffers that allows for dynamically increasing the
batch size in increments of batch.initial.size.
The documented benefit is that we can send large batches when there is lots of
data ready to be sent, while also not having to wait for linger.ms when there
is less data. Comparing this to Jun's suggested approach, it looks the same
except that we get size triggered batches instead of linger when throughput is
low. How big an advantage is that?
An alternative dynamic sizing strategy is one based on fairness. Batches are
dynamically sized in a fair way that more fairly distributes the data of each
partition across the request.
Messages are added to small sub-batches (say 4kb or 16kb) in the accumulator.
When draining the sub-batches in the Sender, the logic selects sub-batches by
creation order repeatedly until constraints are met (like request.size). All
sub-batches of the same partition are grouped into a single batch for sending.
This way the user can set a high batch.size (could even default it to request
size) as the final batches will be fairly distributed across partitions and we
should get good utilisation of the request.size (and still respecting linger).
Example with request.size=128kb, 16kb sub-batches, 1 broker and picking
sub-batches in creation order. None have reached linger in this example for
simplicity.
Accumulator
p0: [sb1{t1},sb2{t2},sb3{t3},sb4{t4},sb5{t5},sb6{t6},sb7{t7},sb8{t8}]
p1: [sb1{t1}]
p2: [sb1{t3}]
p3: [sb1{t7}]
Request 1
p0: [sb1-sb5]
p1: [sb1]
p2: [sb1]
Request 2 (with no additional data having had arrived)
p0: [sb6-sb8]
p3: [sb1]
The downsides are a decent refactoring.
There would need to be changes to the housekeeping of how callbacks are managed
for example. There might be more impact that I am not aware of, I'm fairly new
to this code.
Thanks
Jack
On 2021/12/13 19:15:37 Jun Rao wrote:
> Hi, Lucas,
>
> Thanks for the reply. It would be useful to summarize the benefits of a
> separate batch.max.size. To me, it's not clear why a user would want two
> different batch sizes. In your example, I can understand why a user would
> want to form a batch with a 5ms linger. But why would a user prefer 16K
> batches with 5ms linger, if say 256K is deemed best for throughput?
>
> Thanks,
>
> Jun
>
> On Fri, Dec 10, 2021 at 4:35 PM Lucas Bradstreet <lu...@confluent.io.invalid>
> wrote:
>
> > Hi Jun,
> >
> > One difference compared to increasing the default batch size is that users
> > may actually prefer smaller batches but it makes much less sense to
> > accumulate many small batches if a batch is already sending.
> >
> > For example, imagine a user that prefer 16K batches with 5ms linger.
> > Everything is functioning normally and 16KB batches are being sent. Then
> > there's a 500ms blip for that broker. Do we want to continue to accumulate
> > 16KB batches, each of which requires a round trip, or would we prefer to
> > accumulate larger batches while sending is blocked?
> >
> > I'm not hugely against increasing the default batch.size in general, but
> > batch.max.size does seem to have some nice properties.
> >
> > Thanks,
> >
> > Lucas
> >
> > On Fri, Dec 10, 2021 at 9:42 AM Jun Rao <j...@confluent.io.invalid> wrote:
> >
> > > Hi, Artem, Luke,
> > >
> > > Thanks for the reply.
> > >
> > > 11. If we get rid of batch.max.size and increase the default batch.size,
> > > it's true the behavior is slightly different than before. However, does
> > > that difference matter to most of our users? In your example, if a user
> > > sets linger.ms to 100ms and thinks 256KB is good for throughput, does it
> > > matter to deliver any batch smaller than 256KB before 100ms? I also find
> > it
> > > a bit hard to explain to our users these 3 different settings related to
> > > batch size.
> > >
> > > Thanks,
> > >
> > > Jun
> > >
> > > On Thu, Dec 9, 2021 at 5:47 AM Luke Chen <show...@gmail.com> wrote:
> > >
> > > > Hi Jun,
> > > >
> > > > 11. In addition to Artem's comment, I think the reason to have
> > additional
> > > > "batch.max.size" is to have more flexibility to users.
> > > > For example:
> > > > With linger.ms=100ms, batch.size=16KB, now, we have 20KB of data
> > coming
> > > to
> > > > a partition within 50ms. Now, sender is ready to pick up the batch to
> > > send.
> > > > In current design, we send 16KB data to broker, and keep the remaining
> > > 4KB
> > > > in the producer, to keep accumulating data.
> > > > But after this KIP, user can send the whole 20KB of data together. That
> > > is,
> > > > user can decide if they want to accumulate more data before the sender
> > is
> > > > ready, and send them together, to have higher throughput. The
> > > > "batch.size=16KB" in the proposal, is more like a soft limit, (and
> > > > "batch.max.size" is like a hard limit), or it's like a switch to enable
> > > the
> > > > batch to become ready. Before sender is ready, we can still accumulate
> > > more
> > > > data, and wrap them together to send to broker.
> > > >
> > > > User can increase "batch.size" to 20KB to achieve the same goal in the
> > > > current design, of course. But you can imagine, if the data within
> > 100ms
> > > is
> > > > just 18KB, then the batch of data will wait for 100ms passed to be sent
> > > > out. This "batch.max.size" config will allow more flexible for user
> > > config.
> > > >
> > > > Does that make sense?
> > > >
> > > > Thank you.
> > > > Luke
> > > >
> > > > On Thu, Dec 9, 2021 at 7:53 AM Artem Livshits
> > > > <alivsh...@confluent.io.invalid> wrote:
> > > >
> > > > > Hi Jun,
> > > > >
> > > > > 11. That was my initial thinking as well, but in a discussion some
> > > people
> > > > > pointed out the change of behavior in some scenarios. E.g. if
> > someone
> > > > for
> > > > > some reason really wants batches to be at least 16KB and sets large
> > > > > linger.ms, and most of the time the batches are filled quickly
> > enough
> > > > and
> > > > > they observe a certain latency. Then they upgrade their client with
> > a
> > > > > default size 256KB and the latency increases. This could be seen as
> > a
> > > > > regression. It could be fixed by just reducing linger.ms to specify
> > > the
> > > > > expected latency, but still could be seen as a disruption by some
> > > users.
> > > > > The other reason to have 2 sizes is to avoid allocating large buffers
> > > > > upfront.
> > > > >
> > > > > -Artem
> > > > >
> > > > > On Wed, Dec 8, 2021 at 3:07 PM Jun Rao <j...@confluent.io.invalid>
> > > wrote:
> > > > >
> > > > > > Hi, Artem,
> > > > > >
> > > > > > Thanks for the reply.
> > > > > >
> > > > > > 11. Got it. To me, batch.size is really used for throughput and not
> > > for
> > > > > > latency guarantees. There is no guarantee when 16KB will be
> > > > accumulated.
> > > > > > So, if users want any latency guarantee, they will need to specify
> > > > > > linger.ms accordingly.
> > > > > > Then, batch.size can just be used to tune for throughput.
> > > > > >
> > > > > > 20. Could we also describe the unit of compression? Is
> > > > > > it batch.initial.size, batch.size or batch.max.size?
> > > > > >
> > > > > > Thanks,
> > > > > >
> > > > > > Jun
> > > > > >
> > > > > > On Wed, Dec 8, 2021 at 9:58 AM Artem Livshits
> > > > > > <alivsh...@confluent.io.invalid> wrote:
> > > > > >
> > > > > > > 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
> > > > > > > > > > > > > > > >> >>
> > > > > > > > > > > > > > > >> >
> > > > > > > > > > > > > > > >>
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > >
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