I agree that setting the default auto.offset.reset to earliest makes sense (This was actually a default choice Flume made for its Kafka channel to avoid missing the first messages). However I think, at a minimum, we should also document a recommendation to consider changing the value to none after mirror maker has run to commit its initial offsets.
Setting the value to none ensures you don't replicated the entire topic from scratch in the case offsets are lost or purged due to prolonged downtime or other unforeseen circumstances. Having and auto.offset.reset of none also allows you to ensure you don't miss data. Missing data can occur when auto.offset.reset is set to latest and the offset state was lost before mirrormaker was caught up or data was produced while it was down. I would also suggest considering increasing the default offsets.retention.minutes from 1 day (1440) to 7 days (10080)...or something similar. I have seen a handful of scenarios where an outage lasts longer than a day, the offsets get purged causing the auto.offset.reset to kick in and in the case of earliest, re-replicating billions of messages. On Tue, Jan 17, 2017 at 8:09 PM, Jeff Widman <j...@netskope.com> wrote: > [Moving discussion from users list to dev list] > > I agree with Ewen that it's more sensible for mirrormaker to default to > replicating topics from the earliest offset available, rather than just > replicating from the current offset onward. > > I filed a JIRA ticket https://issues.apache.org/jira/browse/KAFKA-4668 > As well as a PR: https://github.com/apache/kafka/pull/2394 > > Does this need a KIP? > > The main side effect of this change is if you start mirroring a new topic > you can hammer your network until it catches up or until you realize what's > happening and throttle the mirrormaker client. > > Cheers, > Jeff > > > On Thu, Jan 5, 2017 at 7:55 PM, Ewen Cheslack-Postava <e...@confluent.io> > wrote: > > > The basic issue here is just that the auto.offset.reset defaults to > latest, > > right? That's not a very good setting for a mirroring tool and this seems > > like something we might just want to change the default for. It's > debatable > > whether it would even need a KIP. > > > > We have other settings in MM where we override them if they aren't set > > explicitly but we don't want the normal defaults. Most are producer > > properties to avoid duplicates (the acks, retries, max.block.ms, and > > max.in.flight.requests.per.connection settings), but there are a couple > of > > consumer ones too (auto.commit.enable and consumer.timeout.ms). > > > > This is probably something like a 1-line MM patch if someone wants to > > tackle it -- the question of whether it needs a KIP or not is, > > unfortunately, the more complicated question :( > > > > -Ewen > > > > On Thu, Jan 5, 2017 at 1:10 PM, James Cheng <wushuja...@gmail.com> > wrote: > > > > > > > > > On Jan 5, 2017, at 12:57 PM, Jeff Widman <j...@netskope.com> wrote: > > > > > > > > Thanks James and Hans. > > > > > > > > Will this also happen when we expand the number of partitions in a > > topic? > > > > > > > > That also will trigger a rebalance, the consumer won't subscribe to > the > > > > partition until the rebalance finishes, etc. > > > > > > > > So it'd seem that any messages published to the new partition in > > between > > > > the partition creation and the rebalance finishing won't be consumed > by > > > any > > > > consumers that have offset=latest > > > > > > > > > > It hadn't occured to me until you mentioned it, but yes, I think it'd > > also > > > happen in those cases. > > > > > > In the kafka consumer javadocs, they provide a list of things that > would > > > cause a rebalance: > > > http://kafka.apache.org/0101/javadoc/org/apache/kafka/ > clients/consumer/ > > > KafkaConsumer.html#subscribe(java.util.Collection,%20org. > > > apache.kafka.clients.consumer.ConsumerRebalanceListener) < > > > http://kafka.apache.org/0101/javadoc/org/apache/kafka/ > clients/consumer/ > > > KafkaConsumer.html#subscribe(java.util.Collection, > > > org.apache.kafka.clients.consumer.ConsumerRebalanceListener)> > > > > > > "As part of group management, the consumer will keep track of the list > of > > > consumers that belong to a particular group and will trigger a > rebalance > > > operation if one of the following events trigger - > > > > > > Number of partitions change for any of the subscribed list of topics > > > Topic is created or deleted > > > An existing member of the consumer group dies > > > A new member is added to an existing consumer group via the join API > > > " > > > > > > I'm guessing that this would affect any of those scenarios. > > > > > > -James > > > > > > > > > > > > > > > > > > > > > > On Thu, Jan 5, 2017 at 12:40 AM, James Cheng <wushuja...@gmail.com> > > > wrote: > > > > > > > >> Jeff, > > > >> > > > >> Your analysis is correct. I would say that it is known but > unintuitive > > > >> behavior. > > > >> > > > >> As an example of a problem caused by this behavior, it's possible > for > > > >> mirrormaker to miss messages on newly created topics, even thought > it > > > was > > > >> subscribed to them before topics were creted. > > > >> > > > >> See the following JIRAs: > > > >> https://issues.apache.org/jira/browse/KAFKA-3848 < > > > >> https://issues.apache.org/jira/browse/KAFKA-3848> > > > >> https://issues.apache.org/jira/browse/KAFKA-3370 < > > > >> https://issues.apache.org/jira/browse/KAFKA-3370> > > > >> > > > >> -James > > > >> > > > >>> On Jan 4, 2017, at 4:37 PM, h...@confluent.io wrote: > > > >>> > > > >>> This sounds exactly as I would expect things to behave. If you > > consume > > > >> from the beginning I would think you would get all the messages but > > not > > > if > > > >> you consume from the latest offset. You can separately tune the > > metadata > > > >> refresh interval if you want to miss fewer messages but that still > > won't > > > >> get you all messages from the beginning if you don't explicitly > > consume > > > >> from the beginning. > > > >>> > > > >>> Sent from my iPhone > > > >>> > > > >>>> On Jan 4, 2017, at 6:53 PM, Jeff Widman <j...@netskope.com> > wrote: > > > >>>> > > > >>>> I'm seeing consumers miss messages when they subscribe before the > > > topic > > > >> is > > > >>>> actually created. > > > >>>> > > > >>>> Scenario: > > > >>>> 1) kafka 0.10.1.1 cluster with allow-topic no topics, but supports > > > topic > > > >>>> auto-creation as soon as a message is published to the topic > > > >>>> 2) consumer subscribes using topic string or a regex pattern. > > > Currently > > > >> no > > > >>>> topics match. Consumer offset is "latest" > > > >>>> 3) producer publishes to a topic that matches the string or regex > > > >> pattern. > > > >>>> 4) broker immediately creates a topic, writes the message, and > also > > > >>>> notifies the consumer group that a rebalance needs to happen to > > assign > > > >> the > > > >>>> topic_partition to one of the consumers.. > > > >>>> 5) rebalance is fairly quick, maybe a second or so > > > >>>> 6) a consumer is assigned to the newly-created topic_partition > > > >>>> > > > >>>> At this point, we've got a consumer steadily polling the recently > > > >> created > > > >>>> topic_partition. However, the consumer.poll() never returns any > > > messages > > > >>>> published between topic creation and when the consumer was > assigned > > to > > > >> the > > > >>>> topic_partition. I'm guessing this may be because when the > consumer > > is > > > >>>> assigned to the topic_partition it doesn't find any, so it uses > the > > > >> latest > > > >>>> offset, which happens to be after the messages that were published > > to > > > >>>> create the topic. > > > >>>> > > > >>>> This is surprising because the consumer technically was subscribed > > to > > > >> the > > > >>>> topic before the messages were produced, so you'd think the > consumer > > > >> would > > > >>>> receive these messages. > > > >>>> > > > >>>> Is this known behavior? A bug in Kafka broker? Or a bug in my > client > > > >>>> library? > > > >> > > > >> > > > > > > > > > -- Grant Henke Software Engineer | Cloudera gr...@cloudera.com | twitter.com/gchenke | linkedin.com/in/granthenke
