Hi Dong, As per "If the message's offset is below low_watermark, then it should have been deleted by log retention policy." ---> I am not sure if I understand this correctly. Do you mean to say that the low_watermark will be updated only when the log retention fires on the broker?
Thanks, Mayuresh On Tue, Jan 10, 2017 at 2:56 PM, Dong Lin <lindon...@gmail.com> wrote: > Bump up. I am going to initiate the vote If there is no further concern > with the KIP. > > On Fri, Jan 6, 2017 at 11:23 PM, Dong Lin <lindon...@gmail.com> wrote: > > > Hey Mayuresh, > > > > Thanks for the comment. If the message's offset is below low_watermark, > > then it should have been deleted by log retention policy. Thus it is OK > not > > to expose this message to consumer. Does this answer your question? > > > > Thanks, > > Dong > > > > On Fri, Jan 6, 2017 at 4:21 PM, Mayuresh Gharat < > > gharatmayures...@gmail.com> wrote: > > > >> Hi Dong, > >> > >> Thanks for the KIP. > >> > >> I had a question (which might have been answered before). > >> > >> 1) The KIP says that the low_water_mark will be updated periodically by > >> the > >> broker like high_water_mark. > >> Essentially we want to use low_water_mark for cases where an entire > >> segment > >> cannot be deleted because may be the segment_start_offset < PurgeOffset > < > >> segment_end_offset, in which case we will set the low_water_mark to > >> PurgeOffset+1. > >> > >> 2) The KIP also says that messages below low_water_mark will not be > >> exposed > >> for consumers, which does make sense since we want say that data below > >> low_water_mark is purged. > >> > >> Looking at above conditions, does it make sense not to update the > >> low_water_mark periodically but only on PurgeRequest? > >> The reason being, if we update it periodically then as per 2) we will > not > >> be allowing consumers to re-consume data that is not purged but is below > >> low_water_mark. > >> > >> Thanks, > >> > >> Mayuresh > >> > >> > >> On Fri, Jan 6, 2017 at 11:18 AM, Dong Lin <lindon...@gmail.com> wrote: > >> > >> > Hey Jun, > >> > > >> > Thanks for reviewing the KIP! > >> > > >> > 1. The low_watermark will be checkpointed in a new file named > >> > "replication-low-watermark-checkpoint". It will have the same format > >> as > >> > the existing replication-offset-checkpoint file. This allows us the > keep > >> > the existing format of checkpoint files which maps TopicPartition to > >> Long. > >> > I just updated the "Public Interface" section in the KIP wiki to > explain > >> > this file. > >> > > >> > 2. I think using low_watermark from leader to trigger log retention in > >> the > >> > follower will work correctly in the sense that all messages with > offset > >> < > >> > low_watermark can be deleted. But I am not sure that the efficiency is > >> the > >> > same, i.e. offset of messages which should be deleted (i.e. due to > time > >> or > >> > size-based log retention policy) will be smaller than low_watermark > from > >> > the leader. > >> > > >> > For example, say both the follower and the leader have messages with > >> > offsets in range [0, 2000]. If the follower does log rolling slightly > >> later > >> > than leader, the segments on follower would be [0, 1001], [1002, 2000] > >> and > >> > segments on leader would be [0, 1000], [1001, 2000]. After leader > >> deletes > >> > the first segment, the low_watermark would be 1001. Thus the first > >> segment > >> > would stay on follower's disk unnecessarily which may double disk > usage > >> at > >> > worst. > >> > > >> > Since this approach doesn't save us much, I am inclined to not include > >> this > >> > change to keep the KIP simple. > >> > > >> > Dong > >> > > >> > > >> > > >> > On Fri, Jan 6, 2017 at 10:05 AM, Jun Rao <j...@confluent.io> wrote: > >> > > >> > > Hi, Dong, > >> > > > >> > > Thanks for the proposal. Looks good overall. A couple of comments. > >> > > > >> > > 1. Where is the low_watermark checkpointed? Is that > >> > > in replication-offset-checkpoint? If so, do we need to bump up the > >> > version? > >> > > Could you also describe the format change? > >> > > > >> > > 2. For topics with "delete" retention, currently we let each replica > >> > delete > >> > > old segments independently. With low_watermark, we could just let > >> leaders > >> > > delete old segments through the deletion policy and the followers > will > >> > > simply delete old segments based on low_watermark. Not sure if this > >> saves > >> > > much, but is a potential option that may be worth thinking about. > >> > > > >> > > Jun > >> > > > >> > > > >> > > > >> > > On Wed, Jan 4, 2017 at 8:13 AM, radai <radai.rosenbl...@gmail.com> > >> > wrote: > >> > > > >> > > > one more example of complicated config - mirror maker. > >> > > > > >> > > > we definitely cant trust each and every topic owner to configure > >> their > >> > > > topics not to purge before they've been mirrored. > >> > > > which would mean there's a per-topic config (set by the owner) > and a > >> > > > "global" config (where mirror makers are specified) and they need > >> to be > >> > > > "merged". > >> > > > for those topics that _are_ mirrored. > >> > > > which is a changing set of topics thats stored in an external > system > >> > > > outside of kafka. > >> > > > if a topic is taken out of the mirror set the MM offset would be > >> > "frozen" > >> > > > at that point and prevent clean-up for all eternity, unless its > >> > > cleaned-up > >> > > > itself. > >> > > > > >> > > > ... > >> > > > > >> > > > complexity :-) > >> > > > > >> > > > On Wed, Jan 4, 2017 at 8:04 AM, radai <radai.rosenbl...@gmail.com > > > >> > > wrote: > >> > > > > >> > > > > in summary - i'm not opposed to the idea of a per-topic clean up > >> > config > >> > > > > that tracks some set of consumer groups' offsets (which would > >> > probably > >> > > > work > >> > > > > for 80% of use cases), but i definitely see a need to expose a > >> simple > >> > > API > >> > > > > for the more advanced/obscure/custom use cases (the other 20%). > >> > > > > > >> > > > > On Wed, Jan 4, 2017 at 7:54 AM, radai < > radai.rosenbl...@gmail.com > >> > > >> > > > wrote: > >> > > > > > >> > > > >> a major motivation for this KIP is cost savings. > >> > > > >> > >> > > > >> lots of internal systems at LI use kafka as an intermediate > pipe, > >> > and > >> > > > set > >> > > > >> the topic retention period to a "safe enough" amount of time to > >> be > >> > > able > >> > > > to > >> > > > >> recover from crashes/downtime and catch up to "now". this > results > >> > in a > >> > > > few > >> > > > >> days' worth of retention typically. > >> > > > >> > >> > > > >> however, under normal operating conditions the consumers are > >> mostly > >> > > > >> caught-up and so early clean-up enables a big cost savings in > >> > storage. > >> > > > >> > >> > > > >> as for my points: > >> > > > >> > >> > > > >> 1. when discussing implementation options for automatic > clean-up > >> we > >> > > > >> realized that cleaning up by keeping track of offsets stored in > >> > kafka > >> > > > >> requires some per-topic config - you need to specify which > >> groups to > >> > > > track. > >> > > > >> this becomes a problem because: > >> > > > >> 1.1 - relatively complicated code, to be written in the > >> broker. > >> > > > >> 1.2 - configuration needs to be maintained up to date by > >> topic > >> > > > >> "owners" - of which we have thousands. failure to do so would > >> > decrease > >> > > > the > >> > > > >> cost benefit. > >> > > > >> 1.3 - some applications have a "reconsume" / "reinit" / > >> > > "bootstrap" > >> > > > >> workflow where they will reset their offsets to an earlier > value > >> > than > >> > > > the > >> > > > >> one stored. this means that a stored offset of X does not > always > >> > mean > >> > > > you > >> > > > >> can clean up to X-1. think of it as video encoding -some apps > >> have > >> > > "key > >> > > > >> frames" they may seek back to which are before their current > >> offset. > >> > > > >> 1.4 - there are multiple possible strategies - you could > >> clean > >> > up > >> > > > >> aggressively, retain some "time distance" from latest, some > >> "offset > >> > > > >> distance", etc. this we think would have made it very hard to > >> agree > >> > > on a > >> > > > >> single "correct" implementation that everyone would be happy > >> with. > >> > it > >> > > > would > >> > > > >> be better to include the raw functionality in the API and leave > >> the > >> > > > >> "brains" to an external monitoring system where people could > >> > > > custom-taylor > >> > > > >> their logic > >> > > > >> > >> > > > >> 2. ad-hoc consumer groups: its common practice for devs to spin > >> up > >> > > > >> console consumers and connect to a topic as a debug aid. SREs > may > >> > also > >> > > > do > >> > > > >> this. there are also various other eco-system applications that > >> may > >> > > > >> consumer from topics (unknown to topic owners as those are > infra > >> > > > monitoring > >> > > > >> tools). obviously such consumer-groups' offsets should be > ignored > >> > for > >> > > > >> purposes of clean-up, but coming up with a bullet-proof way to > do > >> > this > >> > > > is > >> > > > >> non-trivial and again ties with implementation complexity and > >> > > > inflexibility > >> > > > >> of a "one size fits all" solution in 1.4 above. > >> > > > >> > >> > > > >> 3. forceful clean-up: we have workflows that use kafka to move > >> > > gigantic > >> > > > >> blobs from offline hadoop processing flows into systems. the > data > >> > > being > >> > > > >> "loaded" into such an online system can be several GBs in side > >> and > >> > > take > >> > > > a > >> > > > >> long time to consume (they are sliced into many small msgs). > >> > sometimes > >> > > > the > >> > > > >> sender wants to abort and start a new blob before the current > >> load > >> > > > process > >> > > > >> has completed - meaning the consumer's offsets are not yet > caught > >> > up. > >> > > > >> > >> > > > >> 4. offsets outside of kafka: yes, you could force applications > to > >> > > store > >> > > > >> their offsets twice, but thats inefficient. its better to > expose > >> a > >> > > raw, > >> > > > >> simple API and let such applications manage their own clean-up > >> logic > >> > > > (this > >> > > > >> again ties into 1.4 and no "one size fits all" solution) > >> > > > >> > >> > > > >> On Tue, Jan 3, 2017 at 11:49 PM, Dong Lin <lindon...@gmail.com > > > >> > > wrote: > >> > > > >> > >> > > > >>> On Tue, Jan 3, 2017 at 11:01 PM, Ewen Cheslack-Postava < > >> > > > >>> e...@confluent.io> > >> > > > >>> wrote: > >> > > > >>> > >> > > > >>> > On Tue, Jan 3, 2017 at 6:14 PM, Dong Lin < > lindon...@gmail.com > >> > > >> > > > wrote: > >> > > > >>> > > >> > > > >>> > > Hey Ewen, > >> > > > >>> > > > >> > > > >>> > > Thanks for the review. As Radai explained, it would be > >> complex > >> > in > >> > > > >>> terms > >> > > > >>> > of > >> > > > >>> > > user configuration if we were to use committed offset to > >> decide > >> > > > data > >> > > > >>> > > deletion. We need a way to specify which groups need to > >> consume > >> > > > data > >> > > > >>> of > >> > > > >>> > > this partition. The broker will also need to consume the > >> entire > >> > > > >>> offsets > >> > > > >>> > > topic in that approach which has some overhead. I don't > >> think > >> > it > >> > > is > >> > > > >>> that > >> > > > >>> > > hard to implement. But it will likely take more time to > >> discuss > >> > > > that > >> > > > >>> > > approach due to the new config and the server side > overhead. > >> > > > >>> > > > >> > > > >>> > > We choose to put this API in AdminClient because the API > is > >> > more > >> > > > >>> like an > >> > > > >>> > > administrative operation (such as listGroups, > deleteTopics) > >> > than > >> > > a > >> > > > >>> > consumer > >> > > > >>> > > operation. It is not necessarily called by consumer only. > >> For > >> > > > >>> example, we > >> > > > >>> > > can implement the "delete data before committed offset" > >> > approach > >> > > by > >> > > > >>> > running > >> > > > >>> > > an external service which calls purgeDataBefore() API > based > >> on > >> > > > >>> committed > >> > > > >>> > > offset of consumer groups. > >> > > > >>> > > > >> > > > >>> > > I am not aware that AdminClient is not a public API. > >> Suppose it > >> > > is > >> > > > >>> not > >> > > > >>> > > public now, I assume we plan to make it public in the > >> future as > >> > > > part > >> > > > >>> of > >> > > > >>> > > KIP-4. Are we not making it public because its interface > is > >> not > >> > > > >>> stable? > >> > > > >>> > If > >> > > > >>> > > so, can we just tag this new API as not stable in the > code? > >> > > > >>> > > > >> > > > >>> > > >> > > > >>> > > >> > > > >>> > The AdminClient planned for KIP-4 is a new Java-based > >> > > implementation. > >> > > > >>> It's > >> > > > >>> > definitely confusing that both will be (could be?) named > >> > > AdminClient, > >> > > > >>> but > >> > > > >>> > we've kept the existing Scala AdminClient out of the public > >> API > >> > and > >> > > > >>> have > >> > > > >>> > not required KIPs for changes to it. > >> > > > >>> > > >> > > > >>> > That said, I agree that if this type of API makes it into > >> Kafka, > >> > > > >>> having a > >> > > > >>> > (new, Java-based) AdminClient method would definitely be a > >> good > >> > > idea. > >> > > > >>> An > >> > > > >>> > alternative path might be to have a Consumer-based > >> implementation > >> > > > since > >> > > > >>> > that seems like a very intuitive, natural way to use the > >> > protocol. > >> > > I > >> > > > >>> think > >> > > > >>> > optimizing for the expected use case would be a good idea. > >> > > > >>> > > >> > > > >>> > -Ewen > >> > > > >>> > > >> > > > >>> > Are you saying that the Scala AdminClient is not a public > API > >> and > >> > > we > >> > > > >>> discourage addition of any new feature to this class? > >> > > > >>> > >> > > > >>> I still prefer to add it to AdminClient (Java version in the > >> future > >> > > and > >> > > > >>> Scala version in the short team) because I feel it belongs to > >> admin > >> > > > >>> operation instead of KafkaConsumer interface. For example, if > in > >> > the > >> > > > >>> future > >> > > > >>> we implement the "delete data before committed offset" > strategy > >> in > >> > an > >> > > > >>> external service, I feel it is a bit awkward if the service > has > >> to > >> > > > >>> instantiate a KafkaConsumer and call > >> KafkaConsumer.purgeDataBefore( > >> > > > ...) > >> > > > >>> to > >> > > > >>> purge data. In other words, our expected use-case doesn't > >> > necessarily > >> > > > >>> bind > >> > > > >>> this API with consumer. > >> > > > >>> > >> > > > >>> I am not strong on this issue. Let's see what other > >> > > > committers/developers > >> > > > >>> think about this. > >> > > > >>> > >> > > > >>> > >> > > > >>> > > >> > > > >>> > > > >> > > > >>> > > Thanks, > >> > > > >>> > > Dong > >> > > > >>> > > > >> > > > >>> > > On Tue, Jan 3, 2017 at 3:56 PM, Ewen Cheslack-Postava < > >> > > > >>> e...@confluent.io > >> > > > >>> > > > >> > > > >>> > > wrote: > >> > > > >>> > > > >> > > > >>> > > > Dong, > >> > > > >>> > > > > >> > > > >>> > > > Looks like that's an internal link, > >> > > > >>> > > > https://cwiki.apache.org/confl > >> uence/display/KAFKA/KIP-107% > >> > > > >>> > > > 3A+Add+purgeDataBefore%28%29+API+in+AdminClient > >> > > > >>> > > > is the right one. > >> > > > >>> > > > > >> > > > >>> > > > I have a question about one of the rejected > alternatives: > >> > > > >>> > > > > >> > > > >>> > > > > Using committed offset instead of an extra API to > >> trigger > >> > > data > >> > > > >>> purge > >> > > > >>> > > > operation. > >> > > > >>> > > > > >> > > > >>> > > > The KIP says this would be more complicated to > implement. > >> Why > >> > > is > >> > > > >>> that? > >> > > > >>> > I > >> > > > >>> > > > think brokers would have to consume the entire offsets > >> topic, > >> > > but > >> > > > >>> the > >> > > > >>> > > data > >> > > > >>> > > > stored in memory doesn't seem to change and applying > this > >> > when > >> > > > >>> updated > >> > > > >>> > > > offsets are seen seems basically the same. It might also > >> be > >> > > > >>> possible to > >> > > > >>> > > > make it work even with multiple consumer groups if that > >> was > >> > > > desired > >> > > > >>> > > > (although that'd require tracking more data in memory) > as > >> a > >> > > > >>> > > generalization > >> > > > >>> > > > without requiring coordination between the consumer > >> groups. > >> > > Given > >> > > > >>> the > >> > > > >>> > > > motivation, I'm assuming this was considered unnecessary > >> > since > >> > > > this > >> > > > >>> > > > specifically targets intermediate stream processing > >> topics. > >> > > > >>> > > > > >> > > > >>> > > > Another question is why expose this via AdminClient > (which > >> > > isn't > >> > > > >>> public > >> > > > >>> > > API > >> > > > >>> > > > afaik)? Why not, for example, expose it on the Consumer, > >> > which > >> > > is > >> > > > >>> > > > presumably where you'd want access to it since the > >> > > functionality > >> > > > >>> > depends > >> > > > >>> > > on > >> > > > >>> > > > the consumer actually having consumed the data? > >> > > > >>> > > > > >> > > > >>> > > > -Ewen > >> > > > >>> > > > > >> > > > >>> > > > On Tue, Jan 3, 2017 at 2:45 PM, Dong Lin < > >> > lindon...@gmail.com> > >> > > > >>> wrote: > >> > > > >>> > > > > >> > > > >>> > > > > Hi all, > >> > > > >>> > > > > > >> > > > >>> > > > > We created KIP-107 to propose addition of > >> purgeDataBefore() > >> > > API > >> > > > >>> in > >> > > > >>> > > > > AdminClient. > >> > > > >>> > > > > > >> > > > >>> > > > > Please find the KIP wiki in the link > >> > > > https://iwww.corp.linkedin. > >> > > > >>> > > > > com/wiki/cf/display/ENGS/Kafka > >> +purgeDataBefore%28%29+API+ > >> > > > >>> > > > design+proposal. > >> > > > >>> > > > > We > >> > > > >>> > > > > would love to hear your comments and suggestions. > >> > > > >>> > > > > > >> > > > >>> > > > > Thanks, > >> > > > >>> > > > > Dong > >> > > > >>> > > > > > >> > > > >>> > > > > >> > > > >>> > > > >> > > > >>> > > >> > > > >>> > >> > > > >> > >> > > > >> > >> > > > > > >> > > > > >> > > > >> > > >> > >> > >> > >> -- > >> -Regards, > >> Mayuresh R. Gharat > >> (862) 250-7125 > >> > > > > > -- -Regards, Mayuresh R. Gharat (862) 250-7125
