Jun, On the EOS support, I looked at KIP-98 and it seems to me all the control is specified in the RecordBatch header fields: 1. Whether the batch is a control batch which contains commit or abort marker 2. Whether the batch is transactional which contains PID
In read_committed isolation level mode (I think that's the mode makes sense for mirroring), in the existing code in Fetcher.nextFetchRecord(), the code decides to skip the control batch or the aborted batch based on the abortedTransactions from FetchResponse. This logic would also work in the shallow iterator mode, we would just skip to the next batch. On Thu, Apr 1, 2021 at 9:46 AM Jun Rao <j...@confluent.io.invalid> wrote: > Hi, Henry, > > Thanks for the response. > > 1. I agree with Tom that it's worth thinking about a separate class for > shallow iteration instead of trying to add more complexity into the > existing producer/consumer API. We could potentially make the new class an > internal API if it's only useful for MM. > > 3. I am not sure that we could ignore transactional messages in the first > phase. The usage of EOS is increasing. Also, one can't tell from the > metadata of a topic whether it has EOS data or not. So, there is no easy > way to skip EOS data from the source. > > Jun > > On Thu, Apr 1, 2021 at 1:07 AM Henry Cai <h...@pinterest.com.invalid> > wrote: > > > Jun, > > > > Thanks for your insight looking into this KIP, we do believe the shallow > > iteration will give quite a significant performance boost. > > > > On your concerns: > > > > 1. Cleaner API. One alternative is to create new batch APIs. On > consumer, > > it would become Consumer.pollBatch returns a ConsumerBatch object which > > contains topic/partition/firstOffsetOfBatch/pointerToByteBuffer, > similarly > > Producer.sendBatch(ProducerBatch). Both ConsumerBatch and ProducerBatch > > objects are fixed types (no generics), serializer is gone, interceptors > are > > probably not needed initially (unless people see the need to intercept on > > the batch level). On MM2 side, the current flow is ConsumerRecord -> > > Connect's SourceRecord -> ProducerRecord, we would need to enhance > Connect > > framework to add SourceTask.pollBatch() method which returns a > SourceBatch > > object, so the object conversion flow becomes ConsumerBatch -> > SourceBatch > > -> ProducerBatch, we probably won't support any transformers on Batch > > objects. > > 2. PID/ProducerEpoch/SeqNo passing through RecordBatch. I think those > > transaction fields are only meaningful in the original source kafka > > cluster, producer id/seqNo are not the same for the target kafka cluster. > > So if MM is not going to support transactions at the moment, we can clear > > those fields when they are going through MM. Once MM starts to support > > transactions in the future, it probably will start its own PID/SeqNo etc. > > 3. For EOS and read_committed/read_uncommitted support, we can do phased > > support. Phase 1, don't support transactional messages in the source > > cluster (i.e. abort if it sees control batch records). Phase 2: applying > > commit/abort on the batch boundary level. I am not too familiar with the > > isolation level and abort transaction code path, but it seems the control > > unit is currently on the batch boundary (commit/abort the whole batch), > if > > so, this should also be doable. > > 4. MessageHandler in MM1 or SMT in MM2, initially we don't need to > support > > them. Since now the object is a ConsumerBatch and the existing handler > is > > written for the individual object. Deserialize the batch into individual > > objects would defeat the purpose of performance optimization. > > 5. Multiple batch performances, will do some testing on this. > > > > On Wed, Mar 31, 2021 at 10:14 AM Jun Rao <j...@confluent.io.invalid> > wrote: > > > > > Hi, Henry, > > > > > > Thanks for the KIP. Sorry for the late reply. A few comments below. > > > > > > 1. The 'shallow' feature is potentially useful. I do agree with Tom > that > > > the proposed API changes seem unclean. Quite a few existing stuff don't > > > really work together with this (e.g., generics, serializer, > interceptors, > > > configs like max.poll.records, etc). It's also hard to explain this > > change > > > to the common users of the consumer/producer API. I think it would be > > > useful to explore if there is another cleaner way of adding this. For > > > example, you mentioned that creating a new set of APIs doesn't work for > > > MM2. However, we could potentially change the connect interface to > allow > > > MM2 to use the new API. If this doesn't work, it would be useful to > > explain > > > that in the rejected alternative section. > > > > > > 2. I am not sure that we could pass through all fields in RecordBatch. > > For > > > example, a MM instance could be receiving RecordBatch from different > > source > > > partitions. Mixing the PID/ProducerEpoch/FirstSequence fields across > them > > > in a single producer will be weird. So, it would be useful to document > > this > > > part clearer. > > > > > > 3. EOS. While MM itself doesn't support mirroring data in an > > > exactly-once way, it needs to support reading from a topic with EOS > data. > > > So, it would be useful to document whether both read_committed and > > > read_uncommitted mode are supported and what kind of RecordBatch the > > > consumer returns in each case. > > > > > > 4. With the 'shallow' feature, it seems that some existing features in > MM > > > won't work. For example, I am not sure if SMT works in MM2 > > > and MirrorMakerMessageHandler works in MM1. It would be useful to > > document > > > this kind of impact in the KIP. > > > > > > 5. Multiple batches per partition in the produce request. This seems > not > > > strictly required in KIP-98. However, changing this will probably add a > > bit > > > more complexity in the producer. So, it would be useful to understand > its > > > benefits, especially since it doesn't seem to directly help reduce the > > CPU > > > cost in MM. For example, do you have performance numbers with and > without > > > this enabled in your MM tests? > > > > > > Thanks, > > > > > > Jun > > > > > > On Tue, Mar 30, 2021 at 1:27 PM Henry Cai <h...@pinterest.com.invalid> > > > wrote: > > > > > > > Tom, > > > > > > > > Thanks for your comments. Yes it's a bit clumsy to use the existing > > > > consumer and producer API to carry the underlying record batch, but > > > > creating a new set of API would also mean other use cases (e.g. MM2) > > > > wouldn't be able to use that feature easily. We can throw exceptions > > if > > > we > > > > see clients are setting serializer/compression in the consumer config > > > > option. > > > > > > > > The consumer is essentially getting back a collection of > > > > RecordBatchByteBuffer records and passing them to the producer. Most > > of > > > > the internal APIs inside consumer and producer code paths are > actually > > > > taking on ByteBuffer as the argument so it's not too much work to get > > the > > > > byte buffer through. > > > > > > > > For the worry that the client might see the inside of that byte > buffer, > > > we > > > > can create a RecordBatchByteBufferRecord class to wrap the underlying > > > byte > > > > buffer so hopefully they will not drill too deep into that object. > > > Java's > > > > ByteBuffer does have a asReadOnlyBuffer() method to return a > read-only > > > > buffer, that can be explored as well. > > > > > > > > On Tue, Mar 30, 2021 at 4:24 AM Tom Bentley <tbent...@redhat.com> > > wrote: > > > > > > > > > Hi Henry and Ryanne, > > > > > > > > > > Related to Ismael's point about the producer & consumer configs > being > > > > > dangerous, I can see two parts to this: > > > > > > > > > > 2a. Both the proposed configs seem to be fundamentally incompatible > > > with > > > > > the Producer's existing key.serializer, value.serializer and > > > > > compression.type configs, likewise the consumers key.deserializer > and > > > > > value.deserializer. I don't see a way to avoid this, since those > > > existing > > > > > configs are already separate things. (I did consider whether using > > > > > special-case Deserializer and Serializer could be used instead, but > > > that > > > > > doesn't work nicely; in this use case they're necessarily all > > > configured > > > > > together). I think all we could do would be to reject configs which > > > tried > > > > > to set those existing client configs in conjunction with > > > fetch.raw.bytes > > > > > and send.raw.bytes. > > > > > > > > > > 2b. That still leaves a public Java API which would allow access to > > the > > > > raw > > > > > byte buffers. AFAICS we don't actually need user code to have > access > > to > > > > the > > > > > raw buffers. It would be enough to get an opaque object that > wrapped > > > the > > > > > ByteBuffer from the consumer and pass it to the producer. It's only > > the > > > > > consumer and producer code which needs to be able to obtain the > > wrapped > > > > > buffer. > > > > > > > > > > Kind regards, > > > > > > > > > > Tom > > > > > > > > > > On Tue, Mar 30, 2021 at 8:41 AM Ismael Juma <ism...@juma.me.uk> > > wrote: > > > > > > > > > > > Hi Henry, > > > > > > > > > > > > Can you clarify why this "network performance" issue is only > > related > > > to > > > > > > shallow mirroring? Generally, we want the protocol to be generic > > and > > > > not > > > > > > have a number of special cases. The more special cases you have, > > the > > > > > > tougher it becomes to test all the edge cases. > > > > > > > > > > > > Ismael > > > > > > > > > > > > On Mon, Mar 29, 2021 at 9:51 PM Henry Cai > > <h...@pinterest.com.invalid > > > > > > > > > > wrote: > > > > > > > > > > > > > It's interesting this VOTE thread finally becomes a DISCUSS > > thread. > > > > > > > > > > > > > > For MM2 concern, I will take a look to see whether I can add > the > > > > > support > > > > > > > for MM2. > > > > > > > > > > > > > > For Ismael's concern on multiple batches in the ProduceRequest > > > > > > (conflicting > > > > > > > with KIP-98), here is my take: > > > > > > > > > > > > > > 1. We do need to group multiple batches in the same request > > > otherwise > > > > > the > > > > > > > network performance will suffer. > > > > > > > 2. For the concern on transactional message support as in > KIP-98, > > > > since > > > > > > MM1 > > > > > > > and MM2 currently don't support transactional messages, KIP-712 > > > will > > > > > not > > > > > > > attempt to support transactions either. I will add a config > > option > > > > on > > > > > > > producer config: allowMultipleBatches. By default this option > > will > > > > be > > > > > > off > > > > > > > and the user needs to explicitly turn on this option to use the > > > > shallow > > > > > > > mirror feature. And if we detect both this option and > > transaction > > > is > > > > > > > turned on we will throw an exception to protect current > > transaction > > > > > > > processing. > > > > > > > 3. In the future, when MM2 starts to support exact-once and > > > > > transactional > > > > > > > messages (is that KIP-656?), we can revisit this code. The > > current > > > > > > > transactional message already makes the compromise that the > > > messages > > > > in > > > > > > the > > > > > > > same RecordBatch (MessageSet) are sharing the same > > > > > > > sequence-id/transaction-id, so those messages need to be > > committed > > > > all > > > > > > > together. I think when we support the shallow mirror with > > > > > transactional > > > > > > > semantics, we will group all batches in the same ProduceRequest > > in > > > > the > > > > > > same > > > > > > > transaction boundary, they need to be committed all together. > On > > > the > > > > > > > broker side, all batches coming from ProduceRequest (or > > > > FetchResponse) > > > > > > are > > > > > > > committed in the same log segment file as one unit (current > > > > behavior). > > > > > > > > > > > > > > On Mon, Mar 29, 2021 at 8:46 AM Ryanne Dolan < > > > ryannedo...@gmail.com> > > > > > > > wrote: > > > > > > > > > > > > > > > Ah, I see, thanks Ismael. Now I understand your concern. > > > > > > > > > > > > > > > > From KIP-98, re this change in v3: > > > > > > > > > > > > > > > > "This allows us to remove the message set size since each > > message > > > > set > > > > > > > > already contains a field for the size. More importantly, > since > > > > there > > > > > is > > > > > > > > only one message set to be written to the log, partial > produce > > > > > failures > > > > > > > are > > > > > > > > no longer possible. The full message set is either > successfully > > > > > written > > > > > > > to > > > > > > > > the log (and replicated) or it is not." > > > > > > > > > > > > > > > > The schema and size field don't seem to be an issue, as > KIP-712 > > > > > already > > > > > > > > addresses. > > > > > > > > > > > > > > > > The partial produce failure issue is something I don't > > > understand. > > > > I > > > > > > > can't > > > > > > > > tell if this was done out of convenience at the time or if > > there > > > is > > > > > > > > something incompatible with partial produce success/failure > and > > > > EOS. > > > > > > Does > > > > > > > > anyone know? > > > > > > > > > > > > > > > > Ryanne > > > > > > > > > > > > > > > > On Mon, Mar 29, 2021, 1:41 AM Ismael Juma <ism...@juma.me.uk > > > > > > wrote: > > > > > > > > > > > > > > > > > Ryanne, > > > > > > > > > > > > > > > > > > You misunderstood the referenced comment. It is about the > > > produce > > > > > > > request > > > > > > > > > change to have multiple batches: > > > > > > > > > > > > > > > > > > "Up to ProduceRequest V2, a ProduceRequest can contain > > multiple > > > > > > batches > > > > > > > > of > > > > > > > > > messages stored in the record_set field, but this was > > disabled > > > in > > > > > V3. > > > > > > > We > > > > > > > > > are proposing to bring the multiple batches feature back to > > > > improve > > > > > > the > > > > > > > > > network throughput of the mirror maker producer when the > > > original > > > > > > batch > > > > > > > > > size from source broker is too small." > > > > > > > > > > > > > > > > > > This is unrelated to shallow iteration. > > > > > > > > > > > > > > > > > > Ismael > > > > > > > > > > > > > > > > > > On Sun, Mar 28, 2021, 10:15 PM Ryanne Dolan < > > > > ryannedo...@gmail.com > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > Ismael, I don't think KIP-98 is related. Shallow > iteration > > > was > > > > > > > removed > > > > > > > > in > > > > > > > > > > KAFKA-732, which predates KIP-98 by a few years. > > > > > > > > > > > > > > > > > > > > Ryanne > > > > > > > > > > > > > > > > > > > > On Sun, Mar 28, 2021, 11:25 PM Ismael Juma < > > > ism...@juma.me.uk> > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > Thanks for the KIP. I have a few high level comments: > > > > > > > > > > > > > > > > > > > > > > 1. Like Tom, I'm not convinced about the proposal to > make > > > > this > > > > > > > change > > > > > > > > > to > > > > > > > > > > > MirrorMaker 1 if we intend to deprecate it and remove > > it. I > > > > > would > > > > > > > > > rather > > > > > > > > > > us > > > > > > > > > > > focus our efforts on the implementation we intend to > > > support > > > > > > going > > > > > > > > > > forward. > > > > > > > > > > > 2. The producer/consumer configs seem pretty dangerous > > for > > > > > > general > > > > > > > > > usage, > > > > > > > > > > > but the KIP doesn't address the potential downsides. > > > > > > > > > > > 3. How does the ProducerRequest change impact > > exactly-once > > > > (if > > > > > at > > > > > > > > all)? > > > > > > > > > > The > > > > > > > > > > > change we are reverting was done as part of KIP-98. > Have > > we > > > > > > > > considered > > > > > > > > > > the > > > > > > > > > > > original reasons for the change? > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > Ismael > > > > > > > > > > > > > > > > > > > > > > On Wed, Feb 10, 2021 at 12:58 PM Vahid Hashemian < > > > > > > > > > > > vahid.hashem...@gmail.com> > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > Retitled the thread to conform to the common format. > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Feb 5, 2021 at 4:00 PM Ning Zhang < > > > > > > > ning2008w...@gmail.com> > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > Hello Henry, > > > > > > > > > > > > > > > > > > > > > > > > > > This is a very interesting proposal. > > > > > > > > > > > > > https://issues.apache.org/jira/browse/KAFKA-10728 > > > > reflects > > > > > > the > > > > > > > > > > similar > > > > > > > > > > > > > concern of re-compressing data in mirror maker. > > > > > > > > > > > > > > > > > > > > > > > > > > Probably one thing may need to clarify is: how > > > "shallow" > > > > > > > > mirroring > > > > > > > > > is > > > > > > > > > > > > only > > > > > > > > > > > > > applied to mirrormaker use case, if the changes > need > > to > > > > be > > > > > > made > > > > > > > > on > > > > > > > > > > > > generic > > > > > > > > > > > > > consumer and producer (e.g. by adding > > `fetch.raw.bytes` > > > > and > > > > > > > > > > > > > `send.raw.bytes` to producer and consumer config) > > > > > > > > > > > > > > > > > > > > > > > > > > On 2021/02/05 00:59:57, Henry Cai > > > > > <h...@pinterest.com.INVALID > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > Dear Community members, > > > > > > > > > > > > > > > > > > > > > > > > > > > > We are proposing a new feature to improve the > > > > performance > > > > > > of > > > > > > > > > Kafka > > > > > > > > > > > > mirror > > > > > > > > > > > > > > maker: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-712%3A+Shallow+Mirroring > > > > > > > > > > > > > > > > > > > > > > > > > > > > The current Kafka MirrorMaker process (with the > > > > > underlying > > > > > > > > > Consumer > > > > > > > > > > > and > > > > > > > > > > > > > > Producer library) uses significant CPU cycles and > > > > memory > > > > > to > > > > > > > > > > > > > > decompress/recompress, deserialize/re-serialize > > > > messages > > > > > > and > > > > > > > > copy > > > > > > > > > > > > > multiple > > > > > > > > > > > > > > times of messages bytes along the > > > mirroring/replicating > > > > > > > stages. > > > > > > > > > > > > > > > > > > > > > > > > > > > > The KIP proposes a *shallow mirror* feature which > > > > brings > > > > > > back > > > > > > > > the > > > > > > > > > > > > shallow > > > > > > > > > > > > > > iterator concept to the mirror process and also > > > > proposes > > > > > to > > > > > > > > skip > > > > > > > > > > the > > > > > > > > > > > > > > unnecessary message decompression and > recompression > > > > > steps. > > > > > > > We > > > > > > > > > > argue > > > > > > > > > > > in > > > > > > > > > > > > > > many cases users just want a simple replication > > > > pipeline > > > > > to > > > > > > > > > > replicate > > > > > > > > > > > > the > > > > > > > > > > > > > > message as it is from the source cluster to the > > > > > destination > > > > > > > > > > cluster. > > > > > > > > > > > > In > > > > > > > > > > > > > > many cases the messages in the source cluster are > > > > already > > > > > > > > > > compressed > > > > > > > > > > > > and > > > > > > > > > > > > > > properly batched, users just need an identical > copy > > > of > > > > > the > > > > > > > > > message > > > > > > > > > > > > bytes > > > > > > > > > > > > > > through the mirroring without any transformation > or > > > > > > > > > repartitioning. > > > > > > > > > > > > > > > > > > > > > > > > > > > > We have a prototype implementation in house with > > > > > > MirrorMaker > > > > > > > v1 > > > > > > > > > and > > > > > > > > > > > > > > observed *CPU usage dropped from 50% to 15%* for > > some > > > > > > mirror > > > > > > > > > > > pipelines. > > > > > > > > > > > > > > > > > > > > > > > > > > > > We name this feature: *shallow mirroring* since > it > > > has > > > > > some > > > > > > > > > > > resemblance > > > > > > > > > > > > > to > > > > > > > > > > > > > > the old Kafka 0.7 namesake feature but the > > > > > implementations > > > > > > > are > > > > > > > > > not > > > > > > > > > > > > quite > > > > > > > > > > > > > > the same. ‘*Shallow*’ means 1. we *shallowly* > > > iterate > > > > > > > > > > RecordBatches > > > > > > > > > > > > > inside > > > > > > > > > > > > > > MemoryRecords structure instead of deep iterating > > > > records > > > > > > > > inside > > > > > > > > > > > > > > RecordBatch; 2. We *shallowly* copy (share) > > pointers > > > > > inside > > > > > > > > > > > ByteBuffer > > > > > > > > > > > > > > instead of deep copying and deserializing bytes > > into > > > > > > objects. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Please share discussions/feedback along this > email > > > > > thread. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > > > > > > > > > > > > > > > > Thanks! > > > > > > > > > > > > --Vahid > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
