Hi, Colin, Thanks for the reply. Just a couple of more comments below.
210. Since we are deprecating zookeeper.connection.timeout.ms, should we add a new config to bound the time for a broker to connect to the controller during starting up? 211. BrokerHeartbeat no longer has the state field in the request/response. However, (a) the controller shutdown section still has "In its periodic heartbeats, the broker asks the controller if it can transition into the SHUTDOWN state. This motivates the controller to move all of the leaders off of that broker. Once they are all moved, the controller responds to the heartbeat with a nextState of SHUTDOWN."; (2) the description of BrokerHeartbeat still references currentState and targetState. Jun On Fri, Dec 11, 2020 at 1:33 PM Colin McCabe <cmcc...@apache.org> wrote: > On Wed, Dec 9, 2020, at 10:10, Jun Rao wrote: > > Hi, Colin, > > > > Thanks for the update. A few more follow up comments. > > > > Hi Jun, > > Thanks again for the review. > > > 100. FailedReplicaRecord: Since this is reported by each broker > > independently, perhaps we could use a more concise representation that > has > > a top level broker field, an array of topics, which has an array of > > partitions. > > > > The issue is that there is a size limit on the each record. Putting all > of the partitions of a log directory into a single record would probably > break that in many cases. Still, we can optimize a bit by having an array > of partition IDs, since nearly all the time, we have more than one from the > same topic. > > > 200. Sounds good. If we remove the broker-side fencing logic, do we plan > to > > still keep FENCED in broker state? Do we plan to expose the new states > > through the existing BrokerState metric and if so, what are the values > for > > the new states? > > > > No, we don't need FENCED any more. I have removed it from the KIP. > > The new states are very similar to the current ones, actually. There are > no new states or removed ones. The main change in the broker state machine > is that the RECOVERING_FROM_UNCLEAN_SHUTDOWN state has been renamed to > RECOVERY. Also, unlike previously, the broker will always pass through > RECOVERY (although it may only stay in this state for a very short amount > of time). > > > 201. This may be fine too. Could we document what happens when the > > broker.id/controller.id in metadata.properties don't match the broker > > config when the broker starts up? > > > > I added some documentation about this. > > > 204. There is still "The highest metadata offset which the broker has not > > reached" referenced under BrokerRegistration. > > > > It should be CurrentMetadataOffset. Fixed. > > > 206. Is that separate step needed given KIP-516? With KIP-516 ( > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-516%3A+Topic+Identifiers#KIP516:TopicIdentifiers-LeaderAndIsr > ), > > we don't need to wait for the topic data to be removed from all brokers > > before removing the topic metadata. The combination of unmatching > > topicId > > or the missing topicId from the metadata is enough for the broker to > > clean > > up deleted topics asynchronously. > > It won't be needed once KIP-516 is adopted, but this hasn't been > implemented yet. > > best, > Colin > > > > > Jun > > > > > > > > > > On Tue, Dec 8, 2020 at 5:27 PM Colin McCabe <cmcc...@apache.org> wrote: > > > > > On Thu, Dec 3, 2020, at 16:37, Jun Rao wrote: > > > > Hi, Colin, > > > > > > > > Thanks for the updated KIP. A few more comments below. > > > > > > > > > > Hi Jun, > > > > > > Thanks again for the reviews. > > > > > > > 80.2 For deprecated configs, we need to include zookeeper.* and > > > > broker.id.generation.enable. > > > > > > > > > > Added. > > > > > > > 83.1 If a broker is down, does the controller keep the previously > > > > registered broker epoch forever? If not, how long does the controller > > > keep > > > > it? What does the controller do when receiving a broker heartbeat > request > > > > with an unfound broker epoch? > > > > > > > > > > Yes, the controller keeps the previous registration forever. > > > > > > Broker heartbeat requests with an incorrect broker epoch will be > rejected > > > with STALE_BROKER_EPOCH. > > > > > > > 100. Have you figured out if we need to add a new record type for > > > reporting > > > > partitions on failed disks? > > > > > > > > > > I added FailedReplicaRecord to reflect the case where a JBOD directory > has > > > failed, leading to failed replicas. > > > > > > > 102. For debugging purposes, sometimes it's useful to read the > metadata > > > > topic using tools like console-consumer. Should we support that and > if > > > so, > > > > how? > > > > > > > > > > For now, we have the ability to read the metadata logs with the > dump-logs > > > tool. I think we will come up with some other tools in the future as > we > > > get experience. > > > > > > > 200. "brokers which are fenced will not appear in MetadataResponses. > The > > > > broker will not respond to these requests-- instead, it will simply > > > > disconnect." If the controller is partitioned off from the brokers, > this > > > > design will cause every broker to stop accepting new client > requests. In > > > > contrast, if ZK is partitioned off, the existing behavior is that the > > > > brokers can continue to work based on the last known metadata. So, I > am > > > not > > > > sure if we should change the existing behavior because of the bigger > > > impact > > > > in the new one. Another option is to keep the existing behavior and > > > expose > > > > a metric for fenced brokers so that the operator could be alerted. > > > > > > > > > > I'm skeptical about how well running without ZK currently works. > However, > > > I will move the broker-side fencing into a follow-up KIP. This KIP is > > > already pretty large and there is no hard dependency on this. There > may > > > also be other ways of accomplishing the positive effects of what > > > broker-side fencing, so more discussion is needed. > > > > > > > 201. I read Ron's comment, but I am still not sure the benefit of > keeping > > > > broker.id and controller.id in meta.properties. It seems that we are > > > just > > > > duplicating the same info in two places and have the additional > burden of > > > > making sure the values in the two places are consistent. > > > > > > > > > > I think the reasoning is that having broker.id protects us against > > > accidentally bringing up a broker with a disk from a different > broker. I > > > don't feel strongly about this but it seemed simpler to keep it. > > > > > > > 202. controller.connect.security.protocol: Is this needed since > > > > controller.listener.names and listener.security.protocol.map imply > the > > > > security protocol already? > > > > > > > > > > You're right, this isn't needed. I'll remove it. > > > > > > > 203. registration.heartbeat.interval.ms: It defaults to 2k. ZK uses > 1/3 > > > of > > > > the session timeout for heartbeat. So, given the default 18k for > > > > registration.lease.timeout.ms, should we default > > > > registration.heartbeat.interval.ms to 6k? > > > > > > > > > > 6 seconds seems like a pretty long time between heartbeats. It might > be > > > useful to know when a broker is missing heartbeats, with less time than > > > that. I provisionally set it to 3 seconds (we can always change > later...) > > > > > > I also changed the name of these configurations to " > > > broker.heartbeat.interval.ms" and "broker.registration.timeout.ms" to > try > > > to clarify them a bit. > > > > > > > 204. "The highest metadata offset which the broker has not reached." > It > > > > seems this should be "has reached". > > > > > > > > > > I changed this to "one more than the highest metadata offset which the > > > broker has reached." > > > > > > > 205. UnfenceBrokerRecord and UnregisterBrokerRecord: To me, they > seem to > > > be > > > > the same. Do we need both? > > > > > > > > > > Unregistration means that the broker has been removed from the cluster. > > > That is different than unfencing, which marks the broker as active. > > > > > > > 206. TopicRecord: The Deleting field is used to indicate that the > topic > > > is > > > > being deleted. I am wondering if this is really needed since > RemoveTopic > > > > already indicates the same thing. > > > > > > > > > > RemoveTopic is the last step, that scrubs all metadata about the topic. > > > In order to get to that last step, the topic data needs to removed > from all > > > brokers (after each broker notices that the topic is being deleted). > > > > > > best, > > > Colin > > > > > > > Jun > > > > > > > > On Wed, Dec 2, 2020 at 2:50 PM Colin McCabe <cmcc...@apache.org> > wrote: > > > > > > > > > On Wed, Dec 2, 2020, at 14:07, Ron Dagostino wrote: > > > > > > Hi Colin. Thanks for the updates. It's now clear to me that > brokers > > > > > > keep their broker epoch for the life of their JVM -- they > register > > > > > > once, get their broker epoch in the response, and then never > > > > > > re-register again. Brokers may get fenced, but they keep the > same > > > > > > broker epoch for the life of their JVM. The incarnation ID is > also > > > > > > kept for the life of the JVM but is generated by the broker > itself > > > > > > upon startup, and the combination of the two allows the > Controller to > > > > > > act idempotently if any previously-sent registration response > gets > > > > > > lost. Makes sense. > > > > > > > > > > > > > > > > Thanks, Ron. That's a good summary. > > > > > > > > > > > One thing I wonder about is if it might be helpful for the > broker to > > > > > > send the Cluster ID as determined from its meta.properties file > in > > > its > > > > > > registration request. Does it even make sense for the broker to > > > > > > successfully register and enter the Fenced state if it has the > wrong > > > > > > Cluster ID? > > > > > > > > > > Yeah, that's a good idea. Let's have the broker pass its cluster > ID in > > > > > the registration RPC, and then registration can fail if the broker > is > > > > > configured for the wrong cluster. > > > > > > > > > > > The nextMetadatOffset value that the broker communicates > > > > > > in its registration request only has meaning within the correct > > > > > > cluster, so it feels to me that the Controller should have some > way > > > to > > > > > > perform this sanity check. There is currently (pre-KIP 500) a > check > > > > > > in the broker to make sure its configured cluster ID matches the > one > > > > > > stored in ZooKeeper, and we will have to perform this validation > > > > > > somewhere in the KIP-500 world. If the Controller doesn't do it > > > > > > within the registration request then the broker will have to > make a > > > > > > metadata request to the Controller, retrieve the Cluster ID, and > > > > > > perform the check itself. It feels to me that it might be > better for > > > > > > the Controller to just do it, and then the broker doesn't have to > > > > > > worry about it anymore once it successfully registers. > > > > > > > > > > > > I also have a question about the broker.id value and > > > meta.properties. > > > > > > The KIP now says "In version 0 of meta.properties, there is a > > > > > > broker.id field. Version 1 does not have this field. It is no > > > longer > > > > > > needed because we no longer support dynamic broker id > assignment." > > > > > > But then there is an example version 1 meta.properties file that > > > shows > > > > > > the broker.id value. I actually wonder if maybe the broker.id > value > > > > > > would be good to keep in the version 1 meta.properties file > because > > > it > > > > > > currently (pre-KIP 500, version 0) acts as a sanity check to make > > > sure > > > > > > the broker is using the correct log directory. Similarly with > the > > > > > > controller.id value on controllers -- it would allow the same > type > > > of > > > > > > sanity check for quorum controllers. > > > > > > > > > > > > > > > > That's a good point. I will add broker.id back, and also add > > > > > controller.id as a possibility. > > > > > > > > > > cheers, > > > > > Colin > > > > > > > > > > > > > > > > > On Mon, Nov 30, 2020 at 7:41 PM Colin McCabe <cmcc...@apache.org > > > > > wrote: > > > > > > > > > > > > > > On Fri, Oct 23, 2020, at 16:10, Jun Rao wrote: > > > > > > > > Hi, Colin, > > > > > > > > > > > > > > > > Thanks for the reply. A few more comments. > > > > > > > > > > > > > > Hi Jun, > > > > > > > > > > > > > > Thanks again for the reply. Sorry for the long hiatus. I was > on > > > > > vacation for a while. > > > > > > > > > > > > > > > > > > > > > > > 55. There is still text that favors new broker registration. > > > "When a > > > > > broker > > > > > > > > first starts up, when it is in the INITIAL state, it will > always > > > > > "win" > > > > > > > > broker ID conflicts. However, once it is granted a lease, it > > > > > transitions > > > > > > > > out of the INITIAL state. Thereafter, it may lose subsequent > > > > > conflicts if > > > > > > > > its broker epoch is stale. (See KIP-380 for some background > on > > > > > broker > > > > > > > > epoch.) The reason for favoring new processes is to > accommodate > > > the > > > > > common > > > > > > > > case where a process is killed with kill -9 and then > restarted. > > > We > > > > > want it > > > > > > > > to be able to reclaim its old ID quickly in this case." > > > > > > > > > > > > > > > > > > > > > > Thanks for the reminder. I have clarified the language here. > > > > > Hopefully now it is clear that we don't allow quick re-use of > broker > > > IDs. > > > > > > > > > > > > > > > 80.1 Sounds good. Could you document that listeners is a > required > > > > > config > > > > > > > > now? It would also be useful to annotate other required > configs. > > > For > > > > > > > > example, controller.connect should be required. > > > > > > > > > > > > > > > > > > > > > > I added a note specifying that these are required. > > > > > > > > > > > > > > > 80.2 Could you list all deprecated existing configs? Another > one > > > is > > > > > > > > control.plane.listener.name since the controller no longer > sends > > > > > > > > LeaderAndIsr, UpdateMetadata and StopReplica requests. > > > > > > > > > > > > > > > > > > > > > > I added a section specifying some deprecated configs. > > > > > > > > > > > > > > > 83.1 It seems that the broker can transition from FENCED to > > > RUNNING > > > > > without > > > > > > > > registering for a new broker epoch. I am not sure how this > works. > > > > > Once the > > > > > > > > controller fences a broker, there is no need for the > controller > > > to > > > > > keep the > > > > > > > > boker epoch around. So, if the fenced broker's heartbeat > request > > > > > with the > > > > > > > > existing broker epoch will be rejected, leading the broker > back > > > to > > > > > the > > > > > > > > FENCED state again. > > > > > > > > > > > > > > > > > > > > > > The broker epoch refers to the broker registration. So we DO > keep > > > the > > > > > broker epoch around even while the broker is fenced. > > > > > > > > > > > > > > The broker epoch changes only when there is a new broker > > > > > registration. Fencing or unfencing the broker doesn't change the > > > broker > > > > > epoch. > > > > > > > > > > > > > > > 83.5 Good point on KIP-590. Then should we expose the > controller > > > for > > > > > > > > debugging purposes? If not, we should deprecate the > controllerID > > > > > field in > > > > > > > > MetadataResponse? > > > > > > > > > > > > > > > > > > > > > > I think it's OK to expose it for now, with the proviso that it > > > won't > > > > > be reachable by clients. > > > > > > > > > > > > > > > 90. We rejected the shared ID with just one reason "This is > not a > > > > > good idea > > > > > > > > because NetworkClient assumes a single ID space. So if > there is > > > > > both a > > > > > > > > controller 1 and a broker 1, we don't have a way of picking > the > > > > > "right" > > > > > > > > one." This doesn't seem to be a strong reason. For example, > we > > > could > > > > > > > > address the NetworkClient issue with the node type as you > pointed > > > > > out or > > > > > > > > using the negative value of a broker ID as the controller ID. > > > > > > > > > > > > > > > > > > > > > > It would require a lot of code changes to support multiple > types of > > > > > node IDs. It's not clear to me that the end result would be > better -- > > > I > > > > > tend to think it would be worse, since it would be more complex. > In a > > > > > similar vein, using negative numbers seems dangerous, since we use > > > > > negatives or -1 as "special values" in many places. For example, > -1 > > > often > > > > > represents "no such node." > > > > > > > > > > > > > > One important thing to keep in mind is that we want to be able > to > > > > > transition from a broker and a controller being co-located to them > no > > > > > longer being co-located. This is much easier to do when they have > > > separate > > > > > IDs. > > > > > > > > > > > > > > > 100. In KIP-589 > > > > > > > > < > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-589+Add+API+to+update+Replica+state+in+Controller > > > > > >, > > > > > > > > the broker reports all offline replicas due to a disk > failure to > > > the > > > > > > > > controller. It seems this information needs to be persisted > to > > > the > > > > > > > > metadata > > > > > > > > log. Do we have a corresponding record for that? > > > > > > > > > > > > > > > > > > > > > > Hmm, I have to look into this a little bit more. We may need > a new > > > > > record type. > > > > > > > > > > > > > > > 101. Currently, StopReplica request has 2 modes, without > deletion > > > > > and with > > > > > > > > deletion. The former is used for controlled shutdown and > handling > > > > > disk > > > > > > > > failure, and causes the follower to stop. The latter is for > topic > > > > > deletion > > > > > > > > and partition reassignment, and causes the replica to be > deleted. > > > > > Since we > > > > > > > > are deprecating StopReplica, could we document what triggers > the > > > > > stopping > > > > > > > > of a follower and the deleting of a replica now? > > > > > > > > > > > > > > > > > > > > > > RemoveTopic triggers deletion. In general the functionality of > > > > > StopReplica is subsumed by the metadata records. > > > > > > > > > > > > > > > 102. Should we include the metadata topic in the > > > MetadataResponse? > > > > > If so, > > > > > > > > when it will be included and what will the metadata response > look > > > > > like? > > > > > > > > > > > > > > > > > > > > > > No, it won't be included in the metadata response sent back > from > > > the > > > > > brokers. > > > > > > > > > > > > > > > 103. "The active controller assigns the broker a new broker > > > epoch, > > > > > based on > > > > > > > > the latest committed offset in the log." This seems > inaccurate > > > since > > > > > the > > > > > > > > latest committed offset doesn't always advance on every log > > > append. > > > > > > > > > > > > > > > > > > > > > > Given that the new broker epoch won't be visible until the > commit > > > has > > > > > happened, I have changed this to "the next available offset in the > log" > > > > > > > > > > > > > > > 104. REGISTERING(1) : It says "Otherwise, the broker moves > into > > > the > > > > > FENCED > > > > > > > > state.". It seems this should be RUNNING? > > > > > > > > > > > > > > > > 105. RUNNING: Should we require the broker to catch up to the > > > > > metadata log > > > > > > > > to get into this state? > > > > > > > > > > > > > > For 104 and 105, these sections have been reworked. > > > > > > > > > > > > > > best, > > > > > > > Colin > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > Jun > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Oct 23, 2020 at 1:20 PM Colin McCabe < > cmcc...@apache.org > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > On Wed, Oct 21, 2020, at 05:51, Tom Bentley wrote: > > > > > > > > > > Hi Colin, > > > > > > > > > > > > > > > > > > > > On Mon, Oct 19, 2020, at 08:59, Ron Dagostino wrote: > > > > > > > > > > > > Hi Colin. Thanks for the hard work on this KIP. > > > > > > > > > > > > > > > > > > > > > > > > I have some questions about what happens to a broker > > > when it > > > > > becomes > > > > > > > > > > > > fenced (e.g. because it can't send a heartbeat > request to > > > > > keep its > > > > > > > > > > > > lease). The KIP says "When a broker is fenced, it > cannot > > > > > process any > > > > > > > > > > > > client requests. This prevents brokers which are not > > > > > receiving > > > > > > > > > > > > metadata updates or that are not receiving and > processing > > > > > them fast > > > > > > > > > > > > enough from causing issues to clients." And in the > > > > > description of the > > > > > > > > > > > > FENCED(4) state it likewise says "While in this > state, > > > the > > > > > broker > > > > > > > > > does > > > > > > > > > > > > not respond to client requests." It makes sense > that a > > > > > fenced broker > > > > > > > > > > > > should not accept producer requests -- I assume any > such > > > > > requests > > > > > > > > > > > > would result in NotLeaderOrFollowerException. But > what > > > > > about KIP-392 > > > > > > > > > > > > (fetch from follower) consumer requests? It is > > > conceivable > > > > > that > > > > > > > > > these > > > > > > > > > > > > could continue. Related to that, would a fenced > broker > > > > > continue to > > > > > > > > > > > > fetch data for partitions where it thinks it is a > > > follower? > > > > > Even if > > > > > > > > > > > > it rejects consumer requests it might still continue > to > > > > > fetch as a > > > > > > > > > > > > follower. Might it be helpful to clarify both > decisions > > > > > here? > > > > > > > > > > > > > > > > > > > > > > Hi Ron, > > > > > > > > > > > > > > > > > > > > > > Good question. I think a fenced broker should > continue to > > > > > fetch on > > > > > > > > > > > partitions it was already fetching before it was > fenced, > > > > > unless it > > > > > > > > > hits a > > > > > > > > > > > problem. At that point it won't be able to continue, > > > since it > > > > > doesn't > > > > > > > > > have > > > > > > > > > > > the new metadata. For example, it won't know about > > > leadership > > > > > changes > > > > > > > > > in > > > > > > > > > > > the partitions it's fetching. The rationale for > > > continuing to > > > > > fetch > > > > > > > > > is to > > > > > > > > > > > try to avoid disruptions as much as possible. > > > > > > > > > > > > > > > > > > > > > > I don't think fenced brokers should accept client > requests. > > > > > The issue > > > > > > > > > is > > > > > > > > > > > that the fenced broker may or may not have any data it > is > > > > > supposed to > > > > > > > > > > > have. It may or may not have applied any configuration > > > > > changes, etc. > > > > > > > > > that > > > > > > > > > > > it is supposed to have applied. So it could get pretty > > > > > confusing, and > > > > > > > > > also > > > > > > > > > > > potentially waste the client's time. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > When fenced, how would the broker reply to a client > which did > > > > > make a > > > > > > > > > > request? > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hi Tom, > > > > > > > > > > > > > > > > > > The broker will respond with a retryable error in that > case. > > > Once > > > > > the > > > > > > > > > client has re-fetched its metadata, it will no longer see > the > > > > > fenced broker > > > > > > > > > as part of the cluster. I added a note to the KIP. > > > > > > > > > > > > > > > > > > best, > > > > > > > > > Colin > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > > Tom > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
