Hi Colin, Thanks again for the feedback!
On Mon, Jan 6, 2020 at 12:07 PM Colin McCabe <cmcc...@apache.org> wrote: > Metadata requests don't (always) go to the controller, right? We should > fix the wording in this section. > You're correct, s/controller/broker(s)/. I feel like "Proposed Changes" should come before "Public Interfaces" > here. The new configuration won't make sense to the reader until he or she > has read the "changes" section. Also, it's not clear from the name that > "metadata evict" refers to a span of time. What do you think about " > metadata.eviction.period.ms" as a configuration name? > Sure, makes sense. Updated order and config name. > Where is the "10 seconds" coming from here? The current default for > metadata.max.age.ms is 5 * 60 * 1000 ms, which implies that we want to > refresh every 5 minutes. Definitely not every 10 seconds. > The 10 seconds is another arbitrary value to prevent a large number of RPCs if the target batch size were fixed at 20. For example, if there's 5,000 topics with a 5-minute interval, then instead of issuing an RPC every 1.2 seconds with batch size of 20, it would issue an RPC every 10 seconds with batch size of 167. > Stepping back a little bit, it seems like the big problem you identified > is the O(N^2) behavior of producing to X, then Y, then Z, etc. etc. where > each new produce to a fresh topic triggers a metadata request with all the > preceding topics included. > > Of course we need to send out a metadata request before producing to X, > then Y, then Z, but that request could just specify X, or just specify Y, > etc. etc. In other words, we could decouple decouple the routine metadata > fetch which happens on a 5 minute timer from the need to fetch metadata for > something specific right now. > > I guess my question is, do we really need to allow routine metadata > fetches to "piggyback" on the emergency metadata fetches? It adds a lot of > complexity, and we don't have any benchmarks proving that it's better. > Also, as I understand it, whether we piggyback or not, the number of > metadata fetches is the same, right? > So it's possible to do as you suggest, but I would argue that it'd be more complex with how the code is structured and wouldn't add any extra complexity. The derived metadata class effectively respond to a notification that a metadata RPC is going to be issued, where they return the metadata request structure with topics to refresh, which is decoupled from what generated the event (new topic, stale metadata, periodic refresh alarm). There is also a strict implementation detail that only one metadata request can be outstanding at any time, which lends itself to consolidate complexity in the base metadata class and have the derived use the "listen for next update" model. By maintaining an ordered list of topics by their last metadata refresh time (0 for new topics), it's a matter of pulling from the front of the list to see which topics should be included in the next update. Always include all urgent topics, then include non-urgent (i.e. need to be refreshed soon-ish) up to the target batch size. The number of metadata fetches could be reduced. Assuming a target batch size of 20, a new topic might also refresh 19 other "refresh soon" topics in the same RPC, as opposed to those 19 being handled in a subsequent RPC. Although to counter the above, the batching/piggybacking logic isn't necessarily about reducing the total number of RPCs, but rather to distribute the load more evenly over time. For example, if a large number of topics need to be refreshed at the approximate same time (common for startups cases that hit a large number of topics), the updates are more evenly distributed to avoid a flood. Brian > On Mon, Jan 6, 2020, at 10:26, Lucas Bradstreet wrote: > > +1 (non-binding) > > > > On Thu, Jan 2, 2020 at 11:15 AM Brian Byrne <bby...@confluent.io> wrote: > > > > > Hello all, > > > > > > After further discussion and improvements, I'd like to reinstate the > voting > > > process. > > > > > > The updated KIP: > https://cwiki.apache.org/confluence/display/KAFKA/KIP-526 > > > %3A+Reduce+Producer+Metadata+Lookups+for+Large+Number+of+Topics > > > < > https://cwiki.apache.org/confluence/display/KAFKA/KIP-526%3A+Reduce+Producer+Metadata+Lookups+for+Large+Number+of+Topics > > > > > > > > The continued discussion: > > > > > > > https://lists.apache.org/thread.html/b2f8f830ef04587144cf0840c7d4811bbf0a14f3c459723dbc5acf9e@%3Cdev.kafka.apache.org%3E > > > > > > I'd be happy to address any further comments/feedback. > > > > > > Thanks, > > > Brian > > > > > > On Mon, Dec 9, 2019 at 11:02 PM Guozhang Wang <wangg...@gmail.com> > wrote: > > > > > > > With the concluded summary on the other discussion thread, I'm +1 on > the > > > > proposal. > > > > > > > > Thanks Brian! > > > > > > > > On Tue, Nov 19, 2019 at 8:00 PM deng ziming < > dengziming1...@gmail.com> > > > > wrote: > > > > > > > > > > > > > > > > For new (uncached) topics, one problem here is that we don't know > > > which > > > > > > partition to map a record to in the event that it has a key or > custom > > > > > > partitioner, so the RecordAccumulator wouldn't know which > > > batch/broker > > > > it > > > > > > belongs. We'd need an intermediate record queue that subsequently > > > moved > > > > > the > > > > > > records into RecordAccumulators once metadata resolution was > > > complete. > > > > > For > > > > > > known topics, we don't currently block at all in waitOnMetadata. > > > > > > > > > > > > > > > > You are right, I forget this fact, and the intermediate record > queue > > > will > > > > > help, but I have some questions > > > > > > > > > > if we add an intermediate record queue in KafkaProducer, when > should we > > > > > move the records into RecordAccumulators? > > > > > only NetworkClient is aware of the MetadataResponse, here is the > > > > > hierarchical structure of the related classes: > > > > > KafkaProducer > > > > > Accumulator > > > > > Sender > > > > > NetworkClient > > > > > metadataUpdater.handleCompletedMetadataResponse > > > > > > > > > > so > > > > > 1. we should also add a metadataUpdater to KafkaProducer? > > > > > 2. if the topic really does not exists? the intermediate record > queue > > > > will > > > > > become too large? > > > > > 3. and should we `block` when the intermediate record queue is too > > > large? > > > > > and this will again bring the blocking problem? > > > > > > > > > > > > > > > > > > > > On Wed, Nov 20, 2019 at 12:40 AM Brian Byrne <bby...@confluent.io> > > > > wrote: > > > > > > > > > > > Hi Deng, > > > > > > > > > > > > Thanks for the feedback. > > > > > > > > > > > > On Mon, Nov 18, 2019 at 6:56 PM deng ziming < > > > dengziming1...@gmail.com> > > > > > > wrote: > > > > > > > > > > > > > hi, I reviewed the current code, the ProduceMetadata maintains > an > > > > > expiry > > > > > > > threshold for every topic, every time when we write to a topic > we > > > > will > > > > > > set > > > > > > > the expiry time to -1 to indicate it should be updated, this > does > > > > work > > > > > to > > > > > > > reduce the size of the topic working set, but the producer will > > > > > continue > > > > > > > fetching metadata for these topics in every metadata request > for > > > the > > > > > full > > > > > > > expiry duration. > > > > > > > > > > > > > > > > > > > Indeed, you are correct, I terribly misread the code here. > > > Fortunately > > > > > this > > > > > > was only a minor optimization in the KIP that's no longer > necessary. > > > > > > > > > > > > > > > > > > and we can improve the situation by 2 means: > > > > > > > 1. we maintain a refresh threshold for every topic which > is for > > > > > > example > > > > > > > 0.8 * expiry_threshold, and when we send `MetadataRequest` to > > > brokers > > > > > we > > > > > > > just request unknownLeaderTopics + unknownPartitionTopics + > topics > > > > > > > reach refresh threshold. > > > > > > > > > > > > > > > > > > > Right, this is similar to what I suggested, with a larger window > on > > > the > > > > > > "staleness" that permits for batching to an appropriate size > (except > > > if > > > > > > there's any unknown topics, you'd want to issue the request > > > > immediately). > > > > > > > > > > > > > > > > > > > > > > > > > 2. we don't invoke KafkaProducer#waitOnMetadata when we > call > > > > > > > KafkaProducer#send because of we just send data to > > > RecordAccumulator, > > > > > and > > > > > > > before we send data to brokers we will invoke > > > > > RecordAccumulator#ready(), > > > > > > so > > > > > > > we can only invoke waitOnMetadata to block when (number topics > > > > > > > reach refresh threshold)>(number of all known topics)*0.2. > > > > > > > > > > > > > > > > > > > For new (uncached) topics, one problem here is that we don't know > > > which > > > > > > partition to map a record to in the event that it has a key or > custom > > > > > > partitioner, so the RecordAccumulator wouldn't know which > > > batch/broker > > > > it > > > > > > belongs. We'd need an intermediate record queue that subsequently > > > moved > > > > > the > > > > > > records into RecordAccumulators once metadata resolution was > > > complete. > > > > > For > > > > > > known topics, we don't currently block at all in waitOnMetadata. > > > > > > > > > > > > The last major point of minimizing producer startup metadata > RPCs may > > > > > still > > > > > > need to be improved, but this would be a large improvement on the > > > > current > > > > > > situation. > > > > > > > > > > > > Thanks, > > > > > > Brian > > > > > > > > > > > > > > > > > > > > > > > > > I think the above 2 ways are enough to solve the current > problem. > > > > > > > > > > > > > > On Tue, Nov 19, 2019 at 3:20 AM Colin McCabe < > cmcc...@apache.org> > > > > > wrote: > > > > > > > > > > > > > > > On Mon, Nov 18, 2019, at 10:05, Brian Byrne wrote: > > > > > > > > > On Fri, Nov 15, 2019 at 5:08 PM Colin McCabe < > > > cmcc...@apache.org > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > Two seconds doesn't seem like a reasonable amount of > time to > > > > > leave > > > > > > > for > > > > > > > > the > > > > > > > > > > metadata fetch. Fetching halfway through the expiration > > > period > > > > > > seems > > > > > > > > more > > > > > > > > > > reasonable. It also doesn't require us to create a new > > > > > > configuration > > > > > > > > key, > > > > > > > > > > which is nice. > > > > > > > > > > > > > > > > > > > > Another option is to just do the metadata fetch every > > > > > > > > metadata.max.age.ms, > > > > > > > > > > but not expire the topic until we can't fetch the > metadata > > > for > > > > 2 > > > > > * > > > > > > > > > > metadata.max.age.ms. > > > > > > > > > > > > > > > > > > > > > > > > > > > > I'd expect two seconds to be reasonable in the common case. > > > Keep > > > > in > > > > > > > mind > > > > > > > > > that this doesn't affect correctness, and a control > operation > > > > > > returning > > > > > > > > > cached metadata should be on the order of milliseconds. > > > > > > > > > > > > > > > > > > > > > > > > > Hi Brian, > > > > > > > > > > > > > > > > Thanks again for the KIP. > > > > > > > > > > > > > > > > I think the issue here is not the common case, but the > uncommon > > > > case > > > > > > > where > > > > > > > > the metadata fetch takes longer than expected. In that > case, we > > > > > don't > > > > > > > want > > > > > > > > to be in the position of having our metadata expire because > we > > > > waited > > > > > > too > > > > > > > > long to renew it. > > > > > > > > > > > > > > > > This is one reason why I think that the metadata expiration > time > > > > > should > > > > > > > be > > > > > > > > longer than the metadata refresh time. In fact, it might be > > > worth > > > > > > having > > > > > > > > two separate configuration keys for these two values. I > could > > > > > imagine > > > > > > a > > > > > > > > user who is having trouble with metadata expiration wanting > to > > > > > increase > > > > > > > the > > > > > > > > metadata expiration time, but without increasing the metadata > > > > refresh > > > > > > > > period. In a sense, the metadata expiration time is like > the ZK > > > > > > session > > > > > > > > expiration time. You might want to turn it up if the > cluster is > > > > > > > > experiencing load spikes. > > > > > > > > > > > > > > > > > > > > > > > > > > But to the general > > > > > > > > > point, defining the algorithm would mean enforcing it to > fair > > > > > > accuracy, > > > > > > > > > whereas if the suggestion is that it'll be performed at a > > > > > reasonable > > > > > > > > time, > > > > > > > > > it allows for batching and other optimizations. Perhaps I > > > > shouldn't > > > > > > be > > > > > > > > > regarding what's defined in a KIP to be contractual in > these > > > > cases, > > > > > > but > > > > > > > > you > > > > > > > > > could consider a first implementation to collect topics > whose > > > > > > metadata > > > > > > > > has > > > > > > > > > exceeded (metadata.max.age.ms / 2), and sending the batch > > > once a > > > > > > > > > constituent topic's metadata is near the expiry, or a > > > sufficient > > > > > > number > > > > > > > > of > > > > > > > > > topics have been collected (10? 100? 1000?). > > > > > > > > > > > > > > > > > > > > > > > > > I'm concerned that if we change the metadata caching strategy > > > > without > > > > > > > > discussing it first, it may improve certain workloads but > make > > > > others > > > > > > > > worse. We need to be concrete about what the proposed > strategy > > > is > > > > so > > > > > > > that > > > > > > > > we can really evaluate it. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > We should be specific about what happens if the first few > > > > > metadata > > > > > > > > fetches > > > > > > > > > > fail. Do we use exponential backoff to decide when to > > > resend? > > > > > It > > > > > > > > seems > > > > > > > > > > like we really should, for all the usual reasons (reduce > the > > > > load > > > > > > on > > > > > > > > > > brokers, ride out temporary service disruptions, etc.) > Maybe > > > > we > > > > > > > could > > > > > > > > have > > > > > > > > > > an exponential retry backoff for each broker (in other > words, > > > > we > > > > > > > > should try > > > > > > > > > > to contact a different broker before applying the > backoff.) > > > I > > > > > > think > > > > > > > > this > > > > > > > > > > already sort of happens with the disconnect timeout, but > we > > > > might > > > > > > > need > > > > > > > > a > > > > > > > > > > more general solution. > > > > > > > > > > > > > > > > > > > > > > > > > > > > I don't plan to change this behavior. Currently it retries > > > after > > > > a > > > > > > > fixed > > > > > > > > > value of 'retry.backoff.ms' (defaults to 100 ms). It's > > > possible > > > > > that > > > > > > > > > different brokers are attempted, but I haven't dug into it. > > > > > > > > > > > > > > > > > > > > > > > > > I think it's critical to understand what the current > behavior is > > > > > before > > > > > > > we > > > > > > > > try to change it. The difference between retrying the same > > > broker > > > > > and > > > > > > > > trying a different one has a large impact it has on cluster > load > > > > and > > > > > > > > latency. For what it's worth, I believe the behavior is the > > > second > > > > > > one, > > > > > > > > but it has been a while since I checked. Let's figure this > out. > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks for the clarification. Fully asynchronous is the > way > > > to > > > > > > go, I > > > > > > > > > > agree. I'm having trouble understanding how timeouts are > > > > handled > > > > > > in > > > > > > > > the > > > > > > > > > > KIP. It seems like if we can't fetch the metadata > within the > > > > > > > > designated > > > > > > > > > > metadata timeout, the future / callback should receive a > > > > > > > > TimeoutException > > > > > > > > > > right? We do not want the send call to be deferred > forever > > > if > > > > > > > metadata > > > > > > > > > > can't be fetched. Eventually it should fail if it can't > be > > > > > > > performed. > > > > > > > > > > > > > > > > > > > > I do think this is something that will have to be > mentioned > > > in > > > > > the > > > > > > > > > > compatibility section. There is some code out there > that is > > > > > > probably > > > > > > > > > > prepared to handle a timeout exception from the send > > > function, > > > > > > which > > > > > > > > may > > > > > > > > > > need to be updated to check for a timeout from the > future or > > > > > > > callback. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Correct, a timeout exception would be delivered in the > future. > > > > > Sure, > > > > > > I > > > > > > > > can > > > > > > > > > add that note to the KIP. > > > > > > > > > > > > > > > > > > > > > > > > > Thanks. > > > > > > > > > > > > > > > > best, > > > > > > > > Colin > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > It seems like this is an existing problem. You may fire > off > > > a > > > > > lot > > > > > > of > > > > > > > > send > > > > > > > > > > calls that get blocked because the broker that is the > leader > > > > for > > > > > a > > > > > > > > certain > > > > > > > > > > partition is not responding. I'm not sure that we need > to do > > > > > > > anything > > > > > > > > > > special here. On the other hand, we could make the case > for > > > a > > > > > > > generic > > > > > > > > "max > > > > > > > > > > number of outstanding sends" configuration to prevent > > > surprise > > > > > OOMs > > > > > > > in > > > > > > > > the > > > > > > > > > > existing cases, plus the new one we're adding. But this > > > feels > > > > > > like a > > > > > > > > bit > > > > > > > > > > of a scope expansion. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Right, this is an existing problem, however the > asynchronous > > > send > > > > > > could > > > > > > > > > cause unexpected behavior. For example, if a client pinned > > > > > > > > > topics/partitions to individual send threads, then memory > > > > couldn't > > > > > be > > > > > > > > > exhausted by a single topic since a blocking send would > prevent > > > > > > further > > > > > > > > > records from being buffered on that topic. The compromise > could > > > > be > > > > > > that > > > > > > > > we > > > > > > > > > only ever permit one outstanding record batch for a topic, > > > which > > > > > > would > > > > > > > > keep > > > > > > > > > the code simple and wouldn't permit a single topic to > consume > > > all > > > > > > > > available > > > > > > > > > memory. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > They may be connected, but I'm not sure they should be > the > > > > same. > > > > > > > > Perhaps > > > > > > > > > > expiry should be 4x the typical fetch rate, for example. > > > > > > > > > > > > > > > > > > > > > > > > > > > > That's true. You could also make the case for a faster > expiry > > > > than > > > > > > > > refresh > > > > > > > > > as well. Makes sense to separate this out. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hmm.... are you sure this is an N^2 problem? If you > have T1 > > > > and > > > > > > T2, > > > > > > > > you > > > > > > > > > > fetch metadata for T1 and T2, right? I guess you could > argue > > > > > that > > > > > > we > > > > > > > > often > > > > > > > > > > fetch metadata for partitions we don't care about, but > that > > > > > doesn't > > > > > > > > make it > > > > > > > > > > O(N^2). Maybe there's something about the implementation > > > that > > > > > I'm > > > > > > > > missing. > > > > > > > > > > > > > > > > > > > > > > > > > > > > My apologies, I left out the context. One issue the KIP is > > > trying > > > > > to > > > > > > > > > resolve is the metadata storm that's caused by producers > > > starting > > > > > up. > > > > > > > In > > > > > > > > > the worst case, where the send call is only performed from > a > > > > single > > > > > > > > thread > > > > > > > > > (i.e. no possible batching), fetching metadata for 1K > topics > > > will > > > > > > > > generate > > > > > > > > > 1K RPCs, with payload 1+2+...+1K topics' metadata. Being > smart > > > > > about > > > > > > > the > > > > > > > > > topics being refreshed would still generate 1K RPCs for 1 > topic > > > > > each, > > > > > > > and > > > > > > > > > asynchronous behavior would permit batching (note > steady-state > > > > > > > refreshing > > > > > > > > > doesn't require the asynchronous behavior to batch). > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > In general, we need to take advantage of batching to do > this > > > > well > > > > > > > (one > > > > > > > > > > reason why I think we should steer clear of > ultra-granular > > > > > timeout > > > > > > > > > > tracking). It's best to do 1 RPC asking for 10 topics, > not > > > 10 > > > > > RPCs > > > > > > > > asking > > > > > > > > > > for a single topic each, even if that means some of the > topic > > > > > > > timeouts > > > > > > > > are > > > > > > > > > > not *exactly* aligned with the configured value. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Absolutely, agreed. > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > Brian > > > > > > > > > > > > > > > > > > > > > > > > > > > > best, > > > > > > > > > > Colin > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > Brian > > > > > > > > > > > > > > > > > > > > > > On Mon, Nov 11, 2019 at 11:47 AM Colin McCabe < > > > > > > cmcc...@apache.org> > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > Hi Brian, > > > > > > > > > > > > > > > > > > > > > > > > Thanks for the KIP. > > > > > > > > > > > > > > > > > > > > > > > > Starting the metadata fetch before we need the > result is > > > > > > > > definitely a > > > > > > > > > > > > great idea. This way, the metadata fetch can be > done in > > > > > > parallel > > > > > > > > with > > > > > > > > > > all > > > > > > > > > > > > the other stuff e producer is doing, rather than > forcing > > > > the > > > > > > > > producer > > > > > > > > > > to > > > > > > > > > > > > periodically come to a halt periodically while > metadata > > > is > > > > > > > fetched. > > > > > > > > > > > > > > > > > > > > > > > > Maybe I missed it, but there seemed to be some > details > > > > > missing > > > > > > > > here. > > > > > > > > > > When > > > > > > > > > > > > do we start the metadata fetch? For example, if > topic > > > > > metadata > > > > > > > > expires > > > > > > > > > > > > every 5 minutes, perhaps we should wait 4 minutes, > then > > > > > > starting > > > > > > > > > > fetching > > > > > > > > > > > > the new metadata, which we would expect to arrive by > the > > > 5 > > > > > > minute > > > > > > > > > > > > deadline. Or perhaps we should start the fetch even > > > > earlier, > > > > > > > > around > > > > > > > > > > the > > > > > > > > > > > > 2.5 minute mark. In any case, there should be some > > > > > discussion > > > > > > > > about > > > > > > > > > > what > > > > > > > > > > > > the actual policy is. Given that > metadata.max.age.ms is > > > > > > > > configurable, > > > > > > > > > > > > maybe that policy needs to be expressed in terms of > a > > > > > > percentage > > > > > > > > of > > > > > > > > > > the > > > > > > > > > > > > refresh period rather than in terms of an absolute > delay. > > > > > > > > > > > > > > > > > > > > > > > > The KIP correctly points out that the current > metadata > > > > > fetching > > > > > > > > policy > > > > > > > > > > > > causes us to "[block] in a function that's > advertised as > > > > > > > > asynchronous." > > > > > > > > > > > > However, the KIP doesn't seem to spell out whether we > > > will > > > > > > > > continue to > > > > > > > > > > > > block if metadata can't be found, or if this will be > > > > > abolished. > > > > > > > > > > Clearly, > > > > > > > > > > > > starting the metadata fetch early will reduce > blocking in > > > > the > > > > > > > > common > > > > > > > > > > case, > > > > > > > > > > > > but will there still be blocking in the uncommon case > > > where > > > > > the > > > > > > > > early > > > > > > > > > > fetch > > > > > > > > > > > > doesn't succeed in time? > > > > > > > > > > > > > > > > > > > > > > > > > To address (2), the producer currently maintains > an > > > > expiry > > > > > > > > threshold > > > > > > > > > > > > for > > > > > > > > > > > > > every topic, which is used to remove a topic from > the > > > > > > working > > > > > > > > set > > > > > > > > > > at a > > > > > > > > > > > > > future time (currently hard-coded to 5 minutes, > this > > > > > should > > > > > > be > > > > > > > > > > modified > > > > > > > > > > > > to > > > > > > > > > > > > > use metadata.max.age.ms). While this does work to > > > > reduce > > > > > > the > > > > > > > > size > > > > > > > > > > of > > > > > > > > > > > > the > > > > > > > > > > > > > topic working set, the producer will continue > fetching > > > > > > > metadata > > > > > > > > for > > > > > > > > > > > > these > > > > > > > > > > > > > topics in every metadata request for the full > expiry > > > > > > duration. > > > > > > > > This > > > > > > > > > > > > logic > > > > > > > > > > > > > can be made more intelligent by managing the > expiry > > > from > > > > > > when > > > > > > > > the > > > > > > > > > > topic > > > > > > > > > > > > > was last used, enabling the expiry duration to be > > > > reduced > > > > > to > > > > > > > > improve > > > > > > > > > > > > cases > > > > > > > > > > > > > where a large number of topics are touched > > > > intermittently. > > > > > > > > > > > > > > > > > > > > > > > > Can you clarify this part a bit? It seems like we > have a > > > > > > > metadata > > > > > > > > > > > > expiration policy now for topics, and we will have > one > > > > after > > > > > > this > > > > > > > > KIP, > > > > > > > > > > but > > > > > > > > > > > > they will be somewhat different. But it's not clear > to > > > me > > > > > what > > > > > > > the > > > > > > > > > > > > differences are. > > > > > > > > > > > > > > > > > > > > > > > > In general, if load is a problem, we should probably > > > > consider > > > > > > > > adding > > > > > > > > > > some > > > > > > > > > > > > kind of jitter on the client side. There are > definitely > > > > > cases > > > > > > > > where > > > > > > > > > > people > > > > > > > > > > > > start up a lot of clients at the same time in > parallel > > > and > > > > > > there > > > > > > > > is a > > > > > > > > > > > > thundering herd problem with metadata updates. > Adding > > > > jitter > > > > > > > would > > > > > > > > > > spread > > > > > > > > > > > > the load across time rather than creating a spike > every 5 > > > > > > minutes > > > > > > > > in > > > > > > > > > > this > > > > > > > > > > > > case. > > > > > > > > > > > > > > > > > > > > > > > > best, > > > > > > > > > > > > Colin > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Nov 8, 2019, at 08:59, Ismael Juma wrote: > > > > > > > > > > > > > I think this KIP affects when we block which is > > > actually > > > > > user > > > > > > > > visible > > > > > > > > > > > > > behavior. Right? > > > > > > > > > > > > > > > > > > > > > > > > > > Ismael > > > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Nov 8, 2019, 8:50 AM Brian Byrne < > > > > > > bby...@confluent.io> > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > Hi Guozhang, > > > > > > > > > > > > > > > > > > > > > > > > > > > > Regarding metadata expiry, no access times other > than > > > > the > > > > > > > > initial > > > > > > > > > > > > lookup[1] > > > > > > > > > > > > > > are used for determining when to expire producer > > > > > metadata. > > > > > > > > > > Therefore, > > > > > > > > > > > > > > frequently used topics' metadata will be aged > out and > > > > > > > > subsequently > > > > > > > > > > > > > > refreshed (in a blocking manner) every five > minutes, > > > > and > > > > > > > > > > infrequently > > > > > > > > > > > > used > > > > > > > > > > > > > > topics will be retained for a minimum of five > minutes > > > > and > > > > > > > > currently > > > > > > > > > > > > > > refetched on every metadata update during that > time > > > > > period. > > > > > > > The > > > > > > > > > > > > sentence is > > > > > > > > > > > > > > suggesting that we could reduce the expiry time > to > > > > > improve > > > > > > > the > > > > > > > > > > latter > > > > > > > > > > > > > > without affecting (rather slightly improving) the > > > > former. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Keep in mind that in most all cases, I wouldn't > > > > > anticipate > > > > > > > > much of > > > > > > > > > > a > > > > > > > > > > > > > > difference with producer behavior, and the extra > > > logic > > > > > can > > > > > > be > > > > > > > > > > > > implemented > > > > > > > > > > > > > > to have insignificant cost. It's the > large/dynamic > > > > topic > > > > > > > corner > > > > > > > > > > cases > > > > > > > > > > > > that > > > > > > > > > > > > > > we're trying to improve. > > > > > > > > > > > > > > > > > > > > > > > > > > > > It'd be convenient if the KIP is no longer > necessary. > > > > > > You're > > > > > > > > right > > > > > > > > > > in > > > > > > > > > > > > that > > > > > > > > > > > > > > there's no public API changes and the behavioral > > > > changes > > > > > > are > > > > > > > > > > entirely > > > > > > > > > > > > > > internal. I'd be happy to continue the discussion > > > > around > > > > > > the > > > > > > > > KIP, > > > > > > > > > > but > > > > > > > > > > > > > > unless otherwise objected, it can be retired. > > > > > > > > > > > > > > > > > > > > > > > > > > > > [1] Not entirely accurate, it's actually the > first > > > time > > > > > > when > > > > > > > > the > > > > > > > > > > client > > > > > > > > > > > > > > calculates whether to retain the topic in its > > > metadata. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > Brian > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Thu, Nov 7, 2019 at 4:48 PM Guozhang Wang < > > > > > > > > wangg...@gmail.com> > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hello Brian, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Could you elaborate a bit more on this > sentence: > > > > "This > > > > > > > logic > > > > > > > > can > > > > > > > > > > be > > > > > > > > > > > > made > > > > > > > > > > > > > > > more intelligent by managing the expiry from > when > > > the > > > > > > topic > > > > > > > > was > > > > > > > > > > last > > > > > > > > > > > > > > used, > > > > > > > > > > > > > > > enabling the expiry duration to be reduced to > > > improve > > > > > > cases > > > > > > > > > > where a > > > > > > > > > > > > large > > > > > > > > > > > > > > > number of topics are touched intermittently." > Not > > > > sure > > > > > I > > > > > > > > fully > > > > > > > > > > > > understand > > > > > > > > > > > > > > > the proposal. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Also since now this KIP did not make any > public API > > > > > > changes > > > > > > > > and > > > > > > > > > > the > > > > > > > > > > > > > > > behavioral changes are not considered a public > API > > > > > > contract > > > > > > > > (i.e. > > > > > > > > > > > > how we > > > > > > > > > > > > > > > maintain the topic metadata in producer cache > is > > > > never > > > > > > > > committed > > > > > > > > > > to > > > > > > > > > > > > > > users), > > > > > > > > > > > > > > > I wonder if we still need a KIP for the > proposed > > > > change > > > > > > any > > > > > > > > more? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Guozhang > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Thu, Nov 7, 2019 at 12:43 PM Brian Byrne < > > > > > > > > bby...@confluent.io > > > > > > > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hello all, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I'd like to propose a vote for a producer > change > > > to > > > > > > > improve > > > > > > > > > > > > producer > > > > > > > > > > > > > > > > behavior when dealing with a large number of > > > > topics, > > > > > in > > > > > > > > part by > > > > > > > > > > > > > > reducing > > > > > > > > > > > > > > > > the amount of metadata fetching performed. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The full KIP is provided here: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-526%3A+Reduce+Producer+Metadata+Lookups+for+Large+Number+of+Topics > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > And the discussion thread: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://lists.apache.org/thread.html/b2f8f830ef04587144cf0840c7d4811bbf0a14f3c459723dbc5acf9e@%3Cdev.kafka.apache.org%3E > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > Brian > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > > > > > > > -- Guozhang > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > -- Guozhang > > > > > > > > > >
