Thanks Jun on the feedback, I think I understand the issue/point now. We def can add that on older client version if tombstone marker make the value null to preserve behaviour.
There is one caveats to this: * we have to be clear that data is lost if reading via old client/message format - I don't think this is a big issue as mostly the idea/use case is around meta data transport as such would only be as bad as current situation Re having configurable broker this was to handle cases like you described but in another way by allowing organisation choose the behaviour of the compaction per broker or per topic so they could manage their transition to using tombstone markers. On hind sight it maybe easier to just upgrade and downgrade the messages on version as you propose. Sent using OWA for iPhone ________________________________________ From: Jun Rao <j...@confluent.io> Sent: Tuesday, November 8, 2016 12:34:41 AM To: dev@kafka.apache.org Subject: Re: [DISCUSS] KIP-87 - Add Compaction Tombstone Flag For the use case, one potential use case is for schema registration. For example, in Avro, a null value corresponds to a Null schema. So, if you want to be able to keep the schema id in a delete message, the value can't be null. We could get around this issue by specializing null value during schema registration though. Now for the proposed changes. We probably should preserve client compatibility. If a client application is sending a null value to a compacted topic, ideally, it should work the same after the client upgrades. I am not sure about making the tombstone marker configurable, especially at the topic level. Should we allow users to change the config values back and forth, and what would be the implication? Thanks, Jun On Mon, Nov 7, 2016 at 10:48 AM, Becket Qin <becket....@gmail.com> wrote: > Hi Michael, > > Yes, changing the logic in the log cleaner makes sense. There could be some > other thing worth thinking (e.g. the message size change after conversion), > though. > > The scenario I was thinking is the following: > Imagine a distributed caching system built on top of Kafka. A user is > consuming from a topic and it is guaranteed that if the user consume to the > log end it will get the latest value for all the keys. Currently if the > consumer sees a null value it knows the key has been removed. Now let's say > we rolled out this change. And the producer applies a message with the > tombstone flag set, but the value was not null. When we append that message > to the log I suppose we will not do the down conversion if the broker has > set the message.format.version to the latest. Because the log cleaner won't > touch the active log segment, so that message will be sitting in the active > segment as is. Now when a consumer that hasn't upgraded yet consumes that > tombstone message in the active segment, it seems that the broker will need > to down convert that message to remove the value, right? In this case, we > cannot wait for the log cleaner to do the down conversion because that > message may have already been consumed before the log compaction happens. > > Thanks, > > Jiangjie (Becket) Qin > > > > On Mon, Nov 7, 2016 at 9:59 AM, Michael Pearce <michael.pea...@ig.com> > wrote: > > > Hi Becket, > > > > We were thinking more about having the logic that’s in the method > > shouldRetainMessage configurable via http://kafka.apache.org/ > > documentation.html#brokerconfigs at a broker/topic level. And then > scrap > > auto converting the message, and allow organisations to manage the > rollout > > of enabling of the feature. > > (this isn’t in documentation but in response to the discussion thread as > > an alternative approach to roll out the feature) > > > > Does this make any more sense? > > > > Thanks > > Mike > > > > On 11/3/16, 2:27 PM, "Becket Qin" <becket....@gmail.com> wrote: > > > > Hi Michael, > > > > Do you mean using a new configuration it is just the exiting > > message.format.version config? It seems the message.format.version > > config > > is enough in this case. And the default value would always be the > > latest > > version. > > > > > Message version migration would be handled as like in KIP-32 > > > > Also just want to confirm on this. Today if an old consumer consumes > a > > log > > compacted topic and sees an empty value, it knows that is a > tombstone. > > After we start to use the attribute bit, a tombstone message can > have a > > non-empty value. So by "like in KIP-32" you mean we will remove the > > value > > to down convert the message if the consumer version is old, right? > > > > Thanks. > > > > Jiangjie (Becket) Qin > > > > On Wed, Nov 2, 2016 at 1:37 AM, Michael Pearce < > michael.pea...@ig.com> > > wrote: > > > > > Hi Joel , et al. > > > > > > Any comments on the below idea to handle roll out / compatibility > of > > this > > > feature, using a configuration? > > > > > > Does it make sense/clear? > > > Does it add value? > > > Do we want to enforce flag by default, or value by default, or > both? > > > > > > Cheers > > > Mike > > > > > > > > > On 10/27/16, 4:47 PM, "Michael Pearce" <michael.pea...@ig.com> > > wrote: > > > > > > Thanks, James, I think this is a really good addition to the > KIP > > > details, please feel free to amend the wiki/add the use cases, also > > if any > > > others you think of. I definitely think its worthwhile documenting. > > If you > > > can’t let me know ill add them next week (just leaving for a long > > weekend > > > off) > > > > > > Re Joel and others comments about upgrade and compatibility. > > > > > > Rather than trying to auto manage this. > > > > > > Actually maybe we make a configuration option, both at server > > and per > > > topic level to control the behavior of how the server logic should > > work out > > > if the record, is a tombstone record . > > > > > > e.g. > > > > > > key = compation.tombstone.marker > > > > > > value options: > > > > > > value (continues to use null value as tombstone marker) > > > flag (expects to use the tombstone flag) > > > value_or_flag (if either is true it treats the record as a > > tombstone) > > > > > > This way on upgrade users can keep current behavior, and slowly > > > migrate to the new. Having a transition period of using > > value_or_flag, > > > finally having flag only if an organization wishes to use null > values > > > without it being treated as a tombstone marker (use case noted > below) > > > > > > Having it both global broker level and topic override also > > allows some > > > flexibility here. > > > > > > Cheers > > > Mike > > > > > > > > > > > > > > > > > > > > > On 10/27/16, 8:03 AM, "James Cheng" <wushuja...@gmail.com> > > wrote: > > > > > > This KIP would definitely address a gap in the current > > > functionality, where you currently can't have a tombstone with any > > > associated content. > > > > > > That said, I'd like to talk about use cases, to make sure > > that > > > this is in fact useful. The KIP should be updated with whatever use > > cases > > > we come up with. > > > > > > First of all, an observation: When we speak about log > > compaction, > > > we typically think of "the latest message for a key is retained". > In > > that > > > respect, a delete tombstone (i.e. a message with a null payload) is > > treated > > > the same as any other Kafka message: the latest message is > retained. > > It > > > doesn't matter whether the latest message is null, or if the latest > > message > > > has actual content. In all cases, the last message is retained. > > > > > > The only way a delete tombstone is treated differently from > > other > > > Kafka messages is that it automatically disappears after a while. > > The time > > > of deletion is specified using delete.retention.ms. > > > > > > So what we're really talking about is, do we want to > support > > > messages in a log-compacted topic that auto-delete themselves after > > a while? > > > > > > In a thread from 2015, there was a discussion on > first-class > > > support of headers between Roger Hoover, Felix GV, Jun Rao, and I. > > See > > > thread at https://groups.google.com/d/msg/confluent-platform/ > > > 8xPbjyUE_7E/yQ1AeCufL_gJ <https://groups.google.com/d/ > > > msg/confluent-platform/8xPbjyUE_7E/yQ1AeCufL_gJ> . In that thread, > > Jun > > > raised a good question that I didn't have a good answer for at the > > time: If > > > a message is going to auto-delete itself after a while, how > > important was > > > the message? That is, what information did the message contain that > > was > > > important *for a while* but not so important that it needed to be > > kept > > > around forever? > > > > > > Some use cases that I can think of: > > > > > > 1) Tracability. I would like to know who issued this delete > > > tombstone. It might include the hostname, IP of the producer of the > > delete. > > > 2) Timestamps. I would like to know when this delete was > > issued. > > > This use case is already addressed by the availability of > per-message > > > timestamps that came in 0.10.0 > > > 3) Data provenance. I hope I'm using this phrase correctly, > > but > > > what I mean is, where did this delete come from? What processing > job > > > emitted it? What input to the processing job caused this delete to > be > > > produced? For example, if a record in topic A was processed and > > caused a > > > delete tombstone to be emitted to topic B, I might like the offset > > of the > > > topic A message to be attached to the topic B message. > > > 4) Distributed tracing for stream topologies. This might > be a > > > slight repeat of the above use cases. In the microservices world, > we > > can > > > generate call-graphs of webservices using tools like Zipkin/ > > opentracing.io > > > <http://opentracing.io/>, or something homegrown like > > > https://engineering.linkedin.com/distributed-service-call- > > > graph/real-time-distributed-tracing-website-performance- > and-efficiency > > < > > > https://engineering.linkedin.com/distributed-service-call- > > > graph/real-time-distributed-tracing-website-performance- > > and-efficiency>. > > > I can imagine that you might want to do something similar for > stream > > > processing topologies, where stream processing jobs carry along and > > forward > > > along a globally unique identifier, and a distributed topology > graph > > is > > > generated. > > > 5) Cases where processing a delete requires data that is > not > > > available in the message key. I'm not sure I have a good example of > > this, > > > though. One hand-wavy example might be where I am publishing > > documents into > > > Kafka where the documentId is the message key, and the text > contents > > of the > > > document are in the message body. And I have a consuming job that > > does some > > > analytics on the message body. If that document gets deleted, then > > the > > > consuming job might need the original message body in order to > > "delete" > > > that message's impact from the analytics. But I'm not sure that is > a > > great > > > example. If the consumer was worried about that, the consumer would > > > probably keep the original message around, stored by primary key. > > And then > > > all it would need from a delete message would be the primary key of > > the > > > message. > > > > > > Do people think these are valid use cases? > > > > > > What are other use cases that people can think of? > > > > > > -James > > > > > > > On Oct 26, 2016, at 3:46 PM, Mayuresh Gharat < > > > gharatmayures...@gmail.com> wrote: > > > > > > > > +1 @Joel. > > > > I think a clear migration plan of upgrading and > > downgrading of > > > server and > > > > clients along with handling of issues that Joel > mentioned, > > on > > > the KIP would > > > > be really great. > > > > > > > > Thanks, > > > > > > > > Mayuresh > > > > > > > > On Wed, Oct 26, 2016 at 3:31 PM, Joel Koshy < > > jjkosh...@gmail.com> > > > wrote: > > > > > > > >> I'm not sure why it would be useful, but it should be > > > theoretically > > > >> possible if the attribute bit alone is enough to mark a > > > tombstone. OTOH, we > > > >> could consider that as invalid if we wish. These are > > relevant > > > details that > > > >> I think should be added to the KIP. > > > >> > > > >> Also, in the few odd scenarios that I mentioned we > should > > also > > > consider > > > >> that fetches could be coming from other > yet-to-be-upgraded > > > brokers in a > > > >> cluster that is being upgraded. So we would probably > want > > to > > > continue to > > > >> support nulls as tombstones or down-convert in a way > that > > we > > > are sure works > > > >> with least surprise to fetchers. > > > >> > > > >> There is a slightly vague statement under > "Compatibility, > > > Deprecation, and > > > >> Migration Plan" that could benefit more details: *Logic > > would > > > base on > > > >> current behavior of null value or if tombstone flag set > to > > > true, as such > > > >> wouldn't impact any existing flows simply allow new > > producers > > > to make use > > > >> of the feature*. It is unclear to me based on that > > whether you > > > would > > > >> interpret null as a tombstone if the tombstone attribute > > bit is > > > off. > > > >> > > > >> On Wed, Oct 26, 2016 at 3:10 PM, Xavier Léauté < > > > xav...@confluent.io> > > > >> wrote: > > > >> > > > >>> Does this mean that starting with V4 requests we would > > allow > > > storing null > > > >>> messages in compacted topics? The KIP should probably > > clarify > > > the > > > >> behavior > > > >>> for null messages where the tombstone flag is not net. > > > >>> > > > >>> On Wed, Oct 26, 2016 at 1:32 AM Magnus Edenhill < > > > mag...@edenhill.se> > > > >>> wrote: > > > >>> > > > >>>> 2016-10-25 21:36 GMT+02:00 Nacho Solis > > > <nso...@linkedin.com.invalid>: > > > >>>> > > > >>>>> I think you probably require a MagicByte bump if you > > expect > > > correct > > > >>>>> behavior of the system as a whole. > > > >>>>> > > > >>>>> From a client perspective you want to make sure that > > when you > > > >> deliver a > > > >>>>> message that the broker supports the feature you're > > expecting > > > >>>>> (compaction). So, depending on the behavior of the > > broker on > > > >>>> encountering > > > >>>>> a previously undefined bit flag I would suggest > making > > some > > > change to > > > >>>> make > > > >>>>> certain that flag-based compaction is supported. I'm > > going > > > to guess > > > >>> that > > > >>>>> the MagicByte would do this. > > > >>>>> > > > >>>> > > > >>>> I dont believe this is needed since it is already > > attributed > > > through > > > >> the > > > >>>> request's API version. > > > >>>> > > > >>>> Producer: > > > >>>> * if a client sends ProduceRequest V4 then > > attributes.bit5 > > > indicates a > > > >>>> tombstone > > > >>>> * if a clients sends ProduceRequest <V4 then > > attributes.bit5 > > > is > > > >> ignored > > > >>>> and value==null indicates a tombstone > > > >>>> * in both cases the on-disk messages are stored with > > > attributes.bit5 > > > >> (I > > > >>>> assume?) > > > >>>> > > > >>>> Consumer: > > > >>>> * if a clients sends FetchRequest V4 messages are > > > sendfile():ed > > > >> directly > > > >>>> from disk (with attributes.bit5) > > > >>>> * if a client sends FetchRequest <V4 messages are > > slowpathed > > > and > > > >>>> translated from attributes.bit5 to value=null as > > required. > > > >>>> > > > >>>> > > > >>>> That's my understanding anyway, please correct me if > I'm > > > wrong. > > > >>>> > > > >>>> /Magnus > > > >>>> > > > >>>> > > > >>>> > > > >>>>> On Tue, Oct 25, 2016 at 10:17 AM, Magnus Edenhill < > > > >> mag...@edenhill.se> > > > >>>>> wrote: > > > >>>>> > > > >>>>>> It is safe to assume that a previously undefined > > attributes > > > bit > > > >> will > > > >>> be > > > >>>>>> unset in protocol requests from existing clients, if > > not, > > > such a > > > >>> client > > > >>>>> is > > > >>>>>> already violating the protocol and needs to be > fixed. > > > >>>>>> > > > >>>>>> So I dont see a need for a MagicByte bump, both > > broker and > > > client > > > >> has > > > >>>> the > > > >>>>>> information it needs to construct or parse the > message > > > according to > > > >>>>> request > > > >>>>>> version. > > > >>>>>> > > > >>>>>> > > > >>>>>> 2016-10-25 18:48 GMT+02:00 Michael Pearce < > > > michael.pea...@ig.com>: > > > >>>>>> > > > >>>>>>> Hi Magnus, > > > >>>>>>> > > > >>>>>>> I was wondering if I even needed to change those > > also, as > > > >>> technically > > > >>>>>>> we’re just making use of a non used attribute bit, > > but im > > > not > > > >> 100% > > > >>>> that > > > >>>>>> it > > > >>>>>>> be always false currently. > > > >>>>>>> > > > >>>>>>> If someone can say 100% it will already be set > false > > with > > > current > > > >>> and > > > >>>>>>> historic bit wise masking techniques used over the > > time, > > > we could > > > >>> do > > > >>>>> away > > > >>>>>>> with both, and simply just start to use it. > > Unfortunately > > > I don’t > > > >>>> have > > > >>>>>> that > > > >>>>>>> historic knowledge so was hoping it would be > flagged > > up in > > > this > > > >>>>>> discussion > > > >>>>>>> thread ? > > > >>>>>>> > > > >>>>>>> Cheers > > > >>>>>>> Mike > > > >>>>>>> > > > >>>>>>> On 10/25/16, 5:36 PM, "Magnus Edenhill" < > > > mag...@edenhill.se> > > > >>> wrote: > > > >>>>>>> > > > >>>>>>> Hi Michael, > > > >>>>>>> > > > >>>>>>> With the version bumps for Produce and Fetch > > requests, > > > do you > > > >>>>> really > > > >>>>>>> need > > > >>>>>>> to bump MagicByte too? > > > >>>>>>> > > > >>>>>>> Regards, > > > >>>>>>> Magnus > > > >>>>>>> > > > >>>>>>> > > > >>>>>>> 2016-10-25 18:09 GMT+02:00 Michael Pearce < > > > >>> michael.pea...@ig.com > > > >>>>> : > > > >>>>>>> > > > >>>>>>>> Hi All, > > > >>>>>>>> > > > >>>>>>>> I would like to discuss the following KIP > proposal: > > > >>>>>>>> https://cwiki.apache.org/ > > confluence/display/KAFKA/KIP- > > > >>>>>>>> 87+-+Add+Compaction+Tombstone+Flag > > > >>>>>>>> > > > >>>>>>>> This is off the back of the discussion on KIP-82 > / > > KIP > > > >>> meeting > > > >>>>>>> where it > > > >>>>>>>> was agreed to separate this issue and feature. > See: > > > >>>>>>>> http://mail-archives.apache. > > org/mod_mbox/kafka-dev/201610 > > > . > > > >>>>>>>> mbox/%3cCAJS3ho8OcR==EcxsJ8OP99pD2hz=iiGecWsv- > > > >>>>>>>> EZsBsNyDcKr=g...@mail.gmail.com%3e > > > >>>>>>>> > > > >>>>>>>> Thanks > > > >>>>>>>> Mike > > > >>>>>>>> > > > >>>>>>>> The information contained in this email is > strictly > > > >>>> confidential > > > >>>>>> and > > > >>>>>>> for > > > >>>>>>>> the use of the addressee only, unless otherwise > > indicated. > > > >> If > > > >>>> you > > > >>>>>>> are not > > > >>>>>>>> the intended recipient, please do not read, copy, > > use or > > > >>>> disclose > > > >>>>>> to > > > >>>>>>> others > > > >>>>>>>> this message or any attachment. Please also notify > > the > > > >> sender > > > >>>> by > > > >>>>>>> replying > > > >>>>>>>> to this email or by telephone (+44(020 7896 0011) > > and then > > > >>>> delete > > > >>>>>>> the email > > > >>>>>>>> and any copies of it. Opinions, conclusion (etc) > > that do > > > >> not > > > >>>>> relate > > > >>>>>>> to the > > > >>>>>>>> official business of this company shall be > > understood as > > > >>>> neither > > > >>>>>>> given nor > > > >>>>>>>> endorsed by it. IG is a trading name of IG Markets > > Limited > > > >> (a > > > >>>>>> company > > > >>>>>>>> registered in England and Wales, company number > > 04008957) > > > >> and > > > >>>> IG > > > >>>>>>> Index > > > >>>>>>>> Limited (a company registered in England and > Wales, > > > company > > > >>>>> number > > > >>>>>>>> 01190902). Registered address at Cannon Bridge > > House, 25 > > > >>>> Dowgate > > > >>>>>>> Hill, > > > >>>>>>>> London EC4R 2YA. Both IG Markets Limited (register > > number > > > >>>> 195355) > > > >>>>>>> and IG > > > >>>>>>>> Index Limited (register number 114059) are > > authorised and > > > >>>>> regulated > > > >>>>>>> by the > > > >>>>>>>> Financial Conduct Authority. > > > >>>>>>>> > > > >>>>>>> > > > >>>>>>> > > > >>>>>>> The information contained in this email is strictly > > > confidential > > > >>> and > > > >>>>> for > > > >>>>>>> the use of the addressee only, unless otherwise > > indicated. > > > If you > > > >>> are > > > >>>>> not > > > >>>>>>> the intended recipient, please do not read, copy, > > use or > > > disclose > > > >>> to > > > >>>>>> others > > > >>>>>>> this message or any attachment. Please also notify > > the > > > sender by > > > >>>>> replying > > > >>>>>>> to this email or by telephone (+44(020 7896 0011) > > and then > > > delete > > > >>> the > > > >>>>>> email > > > >>>>>>> and any copies of it. Opinions, conclusion (etc) > > that do > > > not > > > >> relate > > > >>>> to > > > >>>>>> the > > > >>>>>>> official business of this company shall be > > understood as > > > neither > > > >>>> given > > > >>>>>> nor > > > >>>>>>> endorsed by it. IG is a trading name of IG Markets > > Limited > > > (a > > > >>> company > > > >>>>>>> registered in England and Wales, company number > > 04008957) > > > and IG > > > >>>> Index > > > >>>>>>> Limited (a company registered in England and Wales, > > company > > > >> number > > > >>>>>>> 01190902). Registered address at Cannon Bridge > > House, 25 > > > Dowgate > > > >>>> Hill, > > > >>>>>>> London EC4R 2YA. Both IG Markets Limited (register > > number > > > 195355) > > > >>> and > > > >>>>> IG > > > >>>>>>> Index Limited (register number 114059) are > > authorised and > > > >> regulated > > > >>>> by > > > >>>>>> the > > > >>>>>>> Financial Conduct Authority. > > > >>>>>>> > > > >>>>>> > > > >>>>> > > > >>>>> > > > >>>>> > > > >>>>> -- > > > >>>>> Nacho (Ignacio) Solis > > > >>>>> Kafka > > > >>>>> nso...@linkedin.com > > > >>>>> > > > >>>> > > > >>> > > > >> > > > > > > > > > > > > > > > > -- > > > > -Regards, > > > > Mayuresh R. Gharat > > > > (862) 250-7125 > > > > > > > > > > > > The information contained in this email is strictly > confidential > > and > > > for the use of the addressee only, unless otherwise indicated. If > > you are > > > not the intended recipient, please do not read, copy, use or > > disclose to > > > others this message or any attachment. Please also notify the > sender > > by > > > replying to this email or by telephone (+44(020 7896 0011) and then > > delete > > > the email and any copies of it. Opinions, conclusion (etc) that do > > not > > > relate to the official business of this company shall be understood > > as > > > neither given nor endorsed by it. IG is a trading name of IG > Markets > > > Limited (a company registered in England and Wales, company number > > > 04008957) and IG Index Limited (a company registered in England and > > Wales, > > > company number 01190902). Registered address at Cannon Bridge > House, > > 25 > > > Dowgate Hill, London EC4R 2YA. Both IG Markets Limited (register > > number > > > 195355) and IG Index Limited (register number 114059) are > authorised > > and > > > regulated by the Financial Conduct Authority. > > > > > > > > > > > > > > > The information contained in this email is strictly confidential and for > > the use of the addressee only, unless otherwise indicated. If you are not > > the intended recipient, please do not read, copy, use or disclose to > others > > this message or any attachment. Please also notify the sender by replying > > to this email or by telephone (+44(020 7896 0011) and then delete the > email > > and any copies of it. Opinions, conclusion (etc) that do not relate to > the > > official business of this company shall be understood as neither given > nor > > endorsed by it. IG is a trading name of IG Markets Limited (a company > > registered in England and Wales, company number 04008957) and IG Index > > Limited (a company registered in England and Wales, company number > > 01190902). Registered address at Cannon Bridge House, 25 Dowgate Hill, > > London EC4R 2YA. Both IG Markets Limited (register number 195355) and IG > > Index Limited (register number 114059) are authorised and regulated by > the > > Financial Conduct Authority. > > > The information contained in this email is strictly confidential and for the use of the addressee only, unless otherwise indicated. If you are not the intended recipient, please do not read, copy, use or disclose to others this message or any attachment. Please also notify the sender by replying to this email or by telephone (+44(020 7896 0011) and then delete the email and any copies of it. Opinions, conclusion (etc) that do not relate to the official business of this company shall be understood as neither given nor endorsed by it. IG is a trading name of IG Markets Limited (a company registered in England and Wales, company number 04008957) and IG Index Limited (a company registered in England and Wales, company number 01190902). Registered address at Cannon Bridge House, 25 Dowgate Hill, London EC4R 2YA. Both IG Markets Limited (register number 195355) and IG Index Limited (register number 114059) are authorised and regulated by the Financial Conduct Authority.
