Thanks for the feedback Guozhang and Gwen. Gwen, I agree with you on this. I am not sure its something we can/should tackle here. Especially before the release. I can leave the delete flag off of the changes.
What that means for KIP-4, is that a client won't be able to differentiate between a topic that is gone vs marked for deletion. This means a delete and then create action may fail with a topic exists exception...which the user could retry until succeeded. I think that is reasonable, and much safer. After that we can work on creating more tests and improving the delete behavior. On Thu, Apr 7, 2016 at 12:55 PM, Gwen Shapira <g...@confluent.io> wrote: > Given that we are very close to the release, if we are changing the > Metadata cache + topic deletion logic, I'd like a good number of system > tests to appear with the patch. > > On Thu, Apr 7, 2016 at 10:53 AM, Gwen Shapira <g...@confluent.io> wrote: > > > This will change some logic though, right? > > > > IIRC, right now produce/fetch requests to marked-for-deletion topics fail > > because the topics are simple not around. You get a generic "doesn't > exist" > > error. If we keep these topics and add a flag, we'll need to find all the > > places with this implicit logic and correct for it. > > > > And since our tests for topic deletion are clearly inadequate... I'm a > bit > > scared :) > > > > Gwen > > > > On Thu, Apr 7, 2016 at 10:34 AM, Guozhang Wang <wangg...@gmail.com> > wrote: > > > >> Hmm, I think since in the original protocol, metadata response do not > have > >> information for "marked for deleted topics" and hence we want to remove > >> that topic from returning in response by cleaning the metadata cache > once > >> it is marked to deletion. > >> > >> With the new format, I think it is OK to delay the metadata cleaning. > >> > >> Guozhang > >> > >> On Thu, Apr 7, 2016 at 8:35 AM, Grant Henke <ghe...@cloudera.com> > wrote: > >> > >> > I am testing the marked for deletion flag in the metadata and ran into > >> some > >> > challenges. > >> > > >> > It turns out that as soon as a topic is marked for deletion it may be > >> > purged from the metadata cache. This means that Metadata responses > >> > can't/don't return the topic. Though the topic may still exist if its > >> not > >> > ready to be completely deleted or is in the process of being deleted. > >> > > >> > This poses a challenge because a user would have no way to tell if a > >> topic > >> > still exists, and is marked for deletion, other than to try and > >> recreate it > >> > and see a failure. I could change the logic to no longer purge a > message > >> > from the cache until its completely deleted, but I am not sure if that > >> > would impact the clients in some way negatively. Does anyone have > enough > >> > background to say? > >> > > >> > I will dig into this a bit more today, but wanted to throw this out > >> there > >> > for some early feedback. > >> > > >> > Thank you, > >> > Grant > >> > > >> > > >> > On Tue, Apr 5, 2016 at 8:02 PM, Jun Rao <j...@confluent.io> wrote: > >> > > >> > > 5. You will return no error and 4,5,6 as replicas. The response also > >> > > includes a list of live brokers. So the client can figure out 5 is > not > >> > live > >> > > directly w/o relying on the error code. > >> > > > >> > > Thanks, > >> > > > >> > > Jun > >> > > > >> > > On Tue, Apr 5, 2016 at 5:05 PM, Grant Henke <ghe...@cloudera.com> > >> wrote: > >> > > > >> > > > Hi Jun, > >> > > > > >> > > > See my responses below: > >> > > > > >> > > > 2. The issues that I was thinking are the following. (a) Say the > >> > > controller > >> > > > > has topic deletion disabled and a topic deletion request is > >> submitted > >> > > to > >> > > > > ZK. In this case, the controller will ignore this request. > >> However, > >> > the > >> > > > > broker may pick up the topic deletion marker in a transient > >> window. > >> > (b) > >> > > > > Suppose that a topic is deleted and then recreated immediately. > >> It is > >> > > > > possible for a broker to see the newly created topic and then > the > >> > > > previous > >> > > > > topic deletion marker in a transient window. Thinking about > this a > >> > bit > >> > > > > more. Both seem to be transient. So, it may not be a big > concern. > >> > So, I > >> > > > am > >> > > > > ok with this as long as the interim solution is not too > >> complicated. > >> > > > > Another thing to think through. If a topic is marked for > >> deletion, do > >> > > we > >> > > > > still return the partition level metadata? > >> > > > > >> > > > > >> > > > I am not changing anything about the metadata content, only > adding a > >> > > > boolean based on the marked for deletion flag in zookeeper. This > is > >> > > > maintaining the same method that the topics script does today. I > do > >> > think > >> > > > delete improvements should be considered/reviewed. The goal here > is > >> to > >> > > > allow the broker to report the value that its sees, which is the > >> value > >> > in > >> > > > zookeeper. > >> > > > > >> > > > 5. The issue is the following. If you have a partition with 3 > >> replicas > >> > > > > 4,5,6, leader is on replica 4 and replica 5 is down. Currently, > >> the > >> > > > broker > >> > > > > will send a REPLICA_NOT_AVAILABLE error code and only replicas > >> 4,6 in > >> > > the > >> > > > > assigned replicas. It's more intuitive to send no error code and > >> > 4,5,6 > >> > > in > >> > > > > the assigned replicas in this case. > >> > > > > >> > > > > >> > > > Should the list with no error code just be 4,6 since 5 is not > >> > available? > >> > > > > >> > > > > >> > > > On Mon, Apr 4, 2016 at 1:34 PM, Jun Rao <j...@confluent.io> wrote: > >> > > > > >> > > > > Grant, > >> > > > > > >> > > > > 2. The issues that I was thinking are the following. (a) Say the > >> > > > controller > >> > > > > has topic deletion disabled and a topic deletion request is > >> submitted > >> > > to > >> > > > > ZK. In this case, the controller will ignore this request. > >> However, > >> > the > >> > > > > broker may pick up the topic deletion marker in a transient > >> window. > >> > (b) > >> > > > > Suppose that a topic is deleted and then recreated immediately. > >> It is > >> > > > > possible for a broker to see the newly created topic and then > the > >> > > > previous > >> > > > > topic deletion marker in a transient window. Thinking about > this a > >> > bit > >> > > > > more. Both seem to be transient. So, it may not be a big > concern. > >> > So, I > >> > > > am > >> > > > > ok with this as long as the interim solution is not too > >> complicated. > >> > > > > Another thing to think through. If a topic is marked for > >> deletion, do > >> > > we > >> > > > > still return the partition level metadata? > >> > > > > > >> > > > > 3. Your explanation on controller id seems reasonable to me. > >> > > > > > >> > > > > 5. The issue is the following. If you have a partition with 3 > >> > replicas > >> > > > > 4,5,6, leader is on replica 4 and replica 5 is down. Currently, > >> the > >> > > > broker > >> > > > > will send a REPLICA_NOT_AVAILABLE error code and only replicas > >> 4,6 in > >> > > the > >> > > > > assigned replicas. It's more intuitive to send no error code and > >> > 4,5,6 > >> > > in > >> > > > > the assigned replicas in this case. > >> > > > > > >> > > > > Thanks, > >> > > > > > >> > > > > Jun > >> > > > > > >> > > > > On Mon, Apr 4, 2016 at 8:33 AM, Grant Henke < > ghe...@cloudera.com> > >> > > wrote: > >> > > > > > >> > > > > > Hi Jun, > >> > > > > > > >> > > > > > Please See my responses below: > >> > > > > > > >> > > > > > Hmm, I am not sure about the listener approach. It ignores > >> configs > >> > > like > >> > > > > > > enable.topic.deletion and also opens the door for potential > >> > > ordering > >> > > > > > issues > >> > > > > > > since now there are two separate paths for propagating the > >> > metadata > >> > > > to > >> > > > > > the > >> > > > > > > brokers. > >> > > > > > > >> > > > > > > >> > > > > > This mechanism is very similar to how deletes are tracked on > the > >> > > > > controller > >> > > > > > itself. It is also the same way ACLs are tracked on brokers in > >> the > >> > > > > default > >> > > > > > implementation. I am not sure I understand what ordering issue > >> > there > >> > > > > could > >> > > > > > be. This is used to report what topics are marked for > deletion, > >> > which > >> > > > > today > >> > > > > > has no dependency on enable.topic.deletion. I agree that the > >> delete > >> > > > > > mechanism in Kafka has a lot of room for improvement, but the > >> goal > >> > in > >> > > > > this > >> > > > > > change is just to enable reporting it to the user, not to > >> > fix/improve > >> > > > > > existing issues. If you have an alternate approach that does > not > >> > > > require > >> > > > > > major changes to the controller code, I would be open to > >> > investigate > >> > > > it. > >> > > > > > > >> > > > > > Could we just leave out markedForDeletion for now? In the > common > >> > > > > > > case, if a topic is deleted, it will only be in > >> markedForDeletion > >> > > > state > >> > > > > > for > >> > > > > > > a few milli seconds anyway. > >> > > > > > > >> > > > > > > >> > > > > > I don't think we should leave it out. The point of these > >> changes is > >> > > to > >> > > > > > prevent a user from needing to talk directly to zookeeper. We > >> need > >> > a > >> > > > way > >> > > > > > for a user to see if a topic has been marked for deletion. > Given > >> > the > >> > > > > issues > >> > > > > > with the current delete implementation, its fairly common for > a > >> > topic > >> > > > to > >> > > > > > remain marked as deleted for quite some time. > >> > > > > > > >> > > > > > Yes, for those usage, it just seems it's a bit weird for the > >> client > >> > > to > >> > > > > > > issue a MetadataRequest to get the controller info since it > >> > doesn't > >> > > > > need > >> > > > > > > any topic metadata. > >> > > > > > > >> > > > > > > >> > > > > > Why does this seam weird? The MetadataRequest is the request > >> used > >> > to > >> > > > > > discover the cluster and metadata about that cluster > regardless > >> of > >> > > the > >> > > > > > topics you are interested in, if any. In fact, a big > motivation > >> for > >> > > the > >> > > > > > change to allow requesting "no topics" is because the existing > >> > > producer > >> > > > > and > >> > > > > > consumer often want to learn about the cluster without asking > >> for > >> > > topic > >> > > > > > metadata and today that means that they request all topics. > >> > > > > > > >> > > > > > 5. The issue is that for a client, when handling a metadata > >> > response, > >> > > > the > >> > > > > > > natural logic is if there is any error in the response, go > to > >> the > >> > > > error > >> > > > > > > handling path (e.g., back off and refresh metadata). > >> Otherwise, > >> > get > >> > > > the > >> > > > > > > leader info and initiate a request to the leader if leader > is > >> > > > > available. > >> > > > > > If > >> > > > > > > you look at the current logic in > >> > > > MetadataCache.getPartitionMetadata(), > >> > > > > if > >> > > > > > > an assigned replica is not alive, we will send a > >> > > > REPLICA_NOT_AVAILABLE > >> > > > > > > error code in the response. If the client follows the above > >> > logic, > >> > > it > >> > > > > > will > >> > > > > > > keep doing the error handling even though there is nothing > >> wrong > >> > > with > >> > > > > the > >> > > > > > > leader. A better behavior is to simply return the list of > >> replica > >> > > ids > >> > > > > > with > >> > > > > > > no error code in this case. > >> > > > > > > >> > > > > > > >> > > > > > To be sure I understand this correctly. Instead of returning > the > >> > > > complete > >> > > > > > list of replicas, including the ones that errored as > >> unavailable. > >> > You > >> > > > are > >> > > > > > suggesting to drop the unavailable ones and return just the > >> > replicas > >> > > > with > >> > > > > > no-errors and return no error code on the partition. Is that > >> > correct? > >> > > > > > > >> > > > > > Under what scenario does the MetadataCache have a replica that > >> is > >> > not > >> > > > > > available? > >> > > > > > > >> > > > > > Thanks, > >> > > > > > Grant > >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > On Mon, Apr 4, 2016 at 12:25 AM, Jun Rao <j...@confluent.io> > >> wrote: > >> > > > > > > >> > > > > > > Grant, > >> > > > > > > > >> > > > > > > 2. Hmm, I am not sure about the listener approach. It > ignores > >> > > configs > >> > > > > > like > >> > > > > > > enable.topic.deletion and also opens the door for potential > >> > > ordering > >> > > > > > issues > >> > > > > > > since now there are two separate paths for propagating the > >> > metadata > >> > > > to > >> > > > > > the > >> > > > > > > brokers. Could we just leave out markedForDeletion for now? > In > >> > the > >> > > > > common > >> > > > > > > case, if a topic is deleted, it will only be in > >> markedForDeletion > >> > > > state > >> > > > > > for > >> > > > > > > a few milli seconds anyway. > >> > > > > > > > >> > > > > > > 3. Yes, for those usage, it just seems it's a bit weird for > >> the > >> > > > client > >> > > > > to > >> > > > > > > issue a MetadataRequest to get the controller info since it > >> > doesn't > >> > > > > need > >> > > > > > > any topic metadata. > >> > > > > > > > >> > > > > > > 5. The issue is that for a client, when handling a metadata > >> > > response, > >> > > > > the > >> > > > > > > natural logic is if there is any error in the response, go > to > >> the > >> > > > error > >> > > > > > > handling path (e.g., back off and refresh metadata). > >> Otherwise, > >> > get > >> > > > the > >> > > > > > > leader info and initiate a request to the leader if leader > is > >> > > > > available. > >> > > > > > If > >> > > > > > > you look at the current logic in > >> > > > MetadataCache.getPartitionMetadata(), > >> > > > > if > >> > > > > > > an assigned replica is not alive, we will send a > >> > > > REPLICA_NOT_AVAILABLE > >> > > > > > > error code in the response. If the client follows the above > >> > logic, > >> > > it > >> > > > > > will > >> > > > > > > keep doing the error handling even though there is nothing > >> wrong > >> > > with > >> > > > > the > >> > > > > > > leader. A better behavior is to simply return the list of > >> replica > >> > > ids > >> > > > > > with > >> > > > > > > no error code in this case. > >> > > > > > > > >> > > > > > > Thanks, > >> > > > > > > > >> > > > > > > Jun > >> > > > > > > > >> > > > > > > > >> > > > > > > > >> > > > > > > On Sun, Apr 3, 2016 at 6:29 PM, Grant Henke < > >> ghe...@cloudera.com > >> > > > >> > > > > wrote: > >> > > > > > > > >> > > > > > > > Responding to a few of the other comments: > >> > > > > > > > > >> > > > > > > > it seems that you propagated > >> > > > > > > > > the topic deletion marker by having the replicaManager > >> read > >> > > from > >> > > > ZK > >> > > > > > > > > directly. It seems that it would be simpler/consistent > if > >> the > >> > > > > > > controller > >> > > > > > > > > propagates that information directly through > >> > UpdateMetaRequest. > >> > > > > > > > > >> > > > > > > > > >> > > > > > > > I was told that I should not try and modify controller > logic > >> > with > >> > > > > KIP-4 > >> > > > > > > > changes. It was indicated that a larger controller rewrite > >> and > >> > > > > testing > >> > > > > > > was > >> > > > > > > > planned and those changes should be considered then. Since > >> > > marking > >> > > > a > >> > > > > > > topic > >> > > > > > > > for deletion doesn't flow through the controller and > >> therefore > >> > > the > >> > > > > > > > UpdateMetadataRequest, > >> > > > > > > > it would take quite a bit of change. We would need to > >> trigger a > >> > > new > >> > > > > > > > UpdateMetadataRequest > >> > > > > > > > every time a new topic is marked for deletion. > >> > > > > > > > > >> > > > > > > > Instead I added a listener to maintain a cache of the > topic > >> > > > deletion > >> > > > > > > znodes > >> > > > > > > > in the ReplicaManager where the existing > >> UpdateMetadataRequests > >> > > are > >> > > > > > > > handled. This would make it easy to swap out later once > the > >> > data > >> > > > is a > >> > > > > > > part > >> > > > > > > > of that request and have minimal impact in the mean time. > >> > > > > > > > > >> > > > > > > > > >> > > > > > > > > Could you add a description on how controller id will be > >> used > >> > > in > >> > > > > the > >> > > > > > > > > client? > >> > > > > > > > > >> > > > > > > > > >> > > > > > > > I will add it to the wiki. Today metrics are the only way > to > >> > > access > >> > > > > > this > >> > > > > > > > piece of data. It is useful information about the cluster > >> for > >> > > many > >> > > > > > > reasons. > >> > > > > > > > Having programatic access to identify the controller is > >> helpful > >> > > for > >> > > > > > > > automation. For example, It can be used during rolling > >> restart > >> > > > logic > >> > > > > to > >> > > > > > > > shutdown the controller last to prevent multiple fail > overs. > >> > > Beyond > >> > > > > > > > automation, it can be leveraged in KIP-4 to route admin > >> > requests > >> > > to > >> > > > > the > >> > > > > > > > controller broker. > >> > > > > > > > > >> > > > > > > > We had a weird semantic in version 0 of MetadataRequest. > If > >> a > >> > > > replica > >> > > > > > is > >> > > > > > > > > not live, but the leader is live, we return an > >> > > > > > > > > error ReplicaNotAvailableException in the partition > >> metadata. > >> > > > This > >> > > > > > > makes > >> > > > > > > > it > >> > > > > > > > > a bit confusing for the client to parse since it has to > >> first > >> > > > check > >> > > > > > > > whether > >> > > > > > > > > leader is available or not before error code checking. > We > >> > were > >> > > > > > thinking > >> > > > > > > > of > >> > > > > > > > > changing that behavior the next time we bump up the > >> version > >> > of > >> > > > > > > > > MetadataRequest. > >> > > > > > > > > Now that time has come, could you include that in the > >> > proposal? > >> > > > > > > > > >> > > > > > > > > >> > > > > > > > I am not sure I completely follow the issue and requested > >> > change. > >> > > > > Could > >> > > > > > > you > >> > > > > > > > point me to the discussion? > >> > > > > > > > > >> > > > > > > > Thank you, > >> > > > > > > > Grant > >> > > > > > > > > >> > > > > > > > On Sun, Apr 3, 2016 at 8:09 PM, Grant Henke < > >> > ghe...@cloudera.com > >> > > > > >> > > > > > wrote: > >> > > > > > > > > >> > > > > > > > > Hi Jun and Ismael, > >> > > > > > > > > > >> > > > > > > > > Initially I had 2 booleans used to indicate if a topic > was > >> > > > internal > >> > > > > > and > >> > > > > > > > if > >> > > > > > > > > a topic was marked for deletion. To save space on large > >> > > > > deployments, > >> > > > > > > > Ismael > >> > > > > > > > > suggested I break out the internal topics and deleted > >> topics > >> > > into > >> > > > > > their > >> > > > > > > > own > >> > > > > > > > > lists. The idea was that instead of 2 bytes added per > >> topic, > >> > in > >> > > > the > >> > > > > > > > general > >> > > > > > > > > case the lists would be empty. Even in those lists I > still > >> > only > >> > > > > > return > >> > > > > > > > > topics that were requested. In fact on the client side > >> they > >> > are > >> > > > > just > >> > > > > > > > > utilized to translate back to booleans. I do prefer the > >> > > booleans > >> > > > > from > >> > > > > > > an > >> > > > > > > > > expressiveness standpoint but was not strongly > >> opinionated on > >> > > the > >> > > > > > > > > structure. > >> > > > > > > > > > >> > > > > > > > > Thank you, > >> > > > > > > > > Grant > >> > > > > > > > > > >> > > > > > > > > On Sun, Apr 3, 2016 at 8:00 PM, Ismael Juma < > >> > ism...@juma.me.uk > >> > > > > >> > > > > > wrote: > >> > > > > > > > > > >> > > > > > > > >> Hi Jun, > >> > > > > > > > >> > >> > > > > > > > >> A couple of comments inline. > >> > > > > > > > >> > >> > > > > > > > >> On Sun, Apr 3, 2016 at 5:55 PM, Jun Rao < > >> j...@confluent.io> > >> > > > wrote: > >> > > > > > > > >> > >> > > > > > > > >> > 1. It seems a bit weird to return just a list of > >> internal > >> > > > topics > >> > > > > > w/o > >> > > > > > > > the > >> > > > > > > > >> > corresponding metadata. It also seems a bit weird to > >> > return > >> > > > the > >> > > > > > > > internal > >> > > > > > > > >> > topics even if the client doesn't ask for it. > >> > > > > > > > >> > >> > > > > > > > >> > >> > > > > > > > >> Good point. > >> > > > > > > > >> > >> > > > > > > > >> > >> > > > > > > > >> > Would it be better to just > >> > > > > > > > >> > add a flag in topic_metadata to indicate whether it's > >> an > >> > > > > internal > >> > > > > > > > topic > >> > > > > > > > >> or > >> > > > > > > > >> > not, and only include the internal topics when thy > are > >> > asked > >> > > > (or > >> > > > > > all > >> > > > > > > > >> topics > >> > > > > > > > >> > are requested) for? > >> > > > > > > > >> > > >> > > > > > > > >> > >> > > > > > > > >> The disadvantage of this is that we are adding one byte > >> per > >> > > > topic > >> > > > > > even > >> > > > > > > > >> though we have a very small number of internal topics > >> > > > (currently a > >> > > > > > > > single > >> > > > > > > > >> internal topic). It seems a bit wasteful and > >> particularly so > >> > > > when > >> > > > > > > using > >> > > > > > > > >> regex subscriptions (since we have to retrieve all > >> topics in > >> > > > that > >> > > > > > > case). > >> > > > > > > > >> > >> > > > > > > > >> 2. A similar comment on topics_marked_for_deletion. > >> Would it > >> > > be > >> > > > > > better > >> > > > > > > > to > >> > > > > > > > >> > only return them when asked for and just return a new > >> > > > > TopicDeleted > >> > > > > > > > error > >> > > > > > > > >> > code in topic_metadata? > >> > > > > > > > >> > >> > > > > > > > >> > >> > > > > > > > >> I agree that this seems better. > >> > > > > > > > >> > >> > > > > > > > >> Ismael > >> > > > > > > > >> > >> > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > -- > >> > > > > > > > > Grant Henke > >> > > > > > > > > Software Engineer | Cloudera > >> > > > > > > > > gr...@cloudera.com | twitter.com/gchenke | > >> > > > > > linkedin.com/in/granthenke > >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > > >> > > > > > > > > >> > > > > > > > -- > >> > > > > > > > Grant Henke > >> > > > > > > > Software Engineer | Cloudera > >> > > > > > > > gr...@cloudera.com | twitter.com/gchenke | > >> > > > > linkedin.com/in/granthenke > >> > > > > > > > > >> > > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > -- > >> > > > > > Grant Henke > >> > > > > > Software Engineer | Cloudera > >> > > > > > gr...@cloudera.com | twitter.com/gchenke | > >> > > linkedin.com/in/granthenke > >> > > > > > > >> > > > > > >> > > > > >> > > > > >> > > > > >> > > > -- > >> > > > Grant Henke > >> > > > Software Engineer | Cloudera > >> > > > gr...@cloudera.com | twitter.com/gchenke | > >> linkedin.com/in/granthenke > >> > > > > >> > > > >> > > >> > > >> > > >> > -- > >> > Grant Henke > >> > Software Engineer | Cloudera > >> > gr...@cloudera.com | twitter.com/gchenke | linkedin.com/in/granthenke > >> > > >> > >> > >> > >> -- > >> -- Guozhang > >> > > > > > -- Grant Henke Software Engineer | Cloudera gr...@cloudera.com | twitter.com/gchenke | linkedin.com/in/granthenke
