Hey everybody,
We have further iterated on the KIP in the accompanying discussion thread
and I'd like to propose we resume the vote.
Some notable changes:
- we will store reassignment information in the `/brokers/topics/[topic]`
- we will internally use two collections to represent a reassignment -
"addingReplicas" and "removingReplicas". LeaderAndIsr has been updated
accordingly
- the Alter API will still use the "targetReplicas" collection, but the
List API will now return three separate collections - the full replica set,
the replicas we are adding as part of this reassignment ("addingReplicas")
and the replicas we are removing ("removingReplicas")
- cancellation of a reassignment now means a proper rollback of the
assignment to its original state prior to the API call
As always, you can re-read the KIP here
https://cwiki.apache.org/confluence/display/KAFKA/KIP-455%3A+Create+an+Administrative+API+for+Replica+Reassignment
Best,
Stanislav
On Wed, May 22, 2019 at 6:12 PM Colin McCabe <cmcc...@apache.org> wrote:
> Hi George,
>
> Thanks for taking a look. I am working on getting a PR done as a
> proof-of-concept. I'll post it soon. Then we'll finish up the vote.
>
> best,
> Colin
>
> On Tue, May 21, 2019, at 17:33, George Li wrote:
> > Hi Colin,
> >
> > Great! Looking forward to these features. +1 (non-binding)
> >
> > What is the estimated timeline to have this implemented? If any help
> > is needed in the implementation of cancelling reassignments, I can
> > help if there is spare cycle.
> >
> >
> > Thanks,
> > George
> >
> >
> >
> > On Thursday, May 16, 2019, 9:48:56 AM PDT, Colin McCabe
> > <cmcc...@apache.org> wrote:
> >
> > Hi George,
> >
> > Yes, KIP-455 allows the reassignment of individual partitions to be
> > cancelled. I think it's very important for these operations to be at
> > the partition level.
> >
> > best,
> > Colin
> >
> > On Tue, May 14, 2019, at 16:34, George Li wrote:
> > > Hi Colin,
> > >
> > > Thanks for the updated KIP. It has very good improvements of Kafka
> > > reassignment operations.
> > >
> > > One question, looks like the KIP includes the Cancellation of
> > > individual pending reassignments as well when the
> > > AlterPartitionReasisgnmentRequest has empty replicas for the
> > > topic/partition. Will you also be implementing the the partition
> > > cancellation/rollback in the PR ? If yes, it will make KIP-236 (it
> > > has PR already) trivial, since the cancel all pending reassignments,
> > > one just needs to do a ListPartitionRessignmentRequest, then submit
> > > empty replicas for all those topic/partitions in
> > > one AlterPartitionReasisgnmentRequest.
> > >
> > >
> > > Thanks,
> > > George
> > >
> > > On Friday, May 10, 2019, 8:44:31 PM PDT, Colin McCabe
> > > <cmcc...@apache.org> wrote:
> > >
> > > On Fri, May 10, 2019, at 17:34, Colin McCabe wrote:
> > > > On Fri, May 10, 2019, at 16:43, Jason Gustafson wrote:
> > > > > Hi Colin,
> > > > >
> > > > > I think storing reassignment state at the partition level is the
> right move
> > > > > and I also agree that replicas should understand that there is a
> > > > > reassignment in progress. This makes KIP-352 a trivial follow-up
> for
> > > > > example. The only doubt I have is whether the leader and isr znode
> is the
> > > > > right place to store the target reassignment. It is a bit odd to
> keep the
> > > > > target assignment in a separate place from the current assignment,
> right? I
> > > > > assume the thinking is probably that although the current
> assignment should
> > > > > probably be in the leader and isr znode as well, it is hard to
> move the
> > > > > state in a compatible way. Is that right? But if we have no plan
> to remove
> > > > > the assignment znode, do you see a downside to storing the target
> > > > > assignment there as well?
> > > > >
> > > >
> > > > Hi Jason,
> > > >
> > > > That's a good point -- it's probably better to keep the target
> > > > assignment in the same znode as the current assignment, for
> > > > consistency. I'll change the KIP.
> > >
> > > Hi Jason,
> > >
> > > Thanks again for the review.
> > >
> > > I took another look at this, and I think we should stick with the
> > > initial proposal of putting the reassignment state into
> > > /brokers/topics/[topic]/partitions/[partitionId]/state. The reason is
> > > because we'll want to bump the leader epoch for the partition when
> > > changing the reassignment state, and the leader epoch resides in that
> > > znode anyway. I agree there is some inconsistency here, but so be it:
> > > if we were to greenfield these zookeeper data structures, we might do
> > > it differently, but the proposed scheme will work fine and be
> > > extensible for the future.
> > >
> > > >
> > > > > A few additional questions:
> > > > >
> > > > > 1. Should `alterPartitionReassignments` be
> `alterPartitionAssignments`?
> > > > > It's the current assignment we're altering, right?
> > > >
> > > > That's fair. AlterPartitionAssigments reads a little better, and
> I'll
> > > > change it to that.
> > >
> > > +1. I've changed the RPC and API name in the wiki.
> > >
> > > >
> > > > > 2. Does this change affect the Metadata API? In other words, are
> clients
> > > > > aware of reassignments? If so, then we probably need a change to
> > > > > UpdateMetadata as well. The only alternative I can think of would
> be to
> > > > > represent the replica set in the Metadata request as the union of
> the
> > > > > current and target replicas, but I can't think of any benefit to
> hiding
> > > > > reassignments. Note that if we did this, we probably wouldn't need
> a
> > > > > separate API to list reassignments.
> > > >
> > > > I thought about this a bit... and I think on balance, you're right.
> We
> > > > should keep this information together with the replica nodes, isr
> > > > nodes, and offline replicas, and that information is available in
> the
> > > > MetadataResponse.
> > > > However, I do think in order to do this, we'll need a flag in the
> > > > MetadataRequest that specifiies "only show me reassigning
> partitions".
> > > > I'll add this.
> > >
> > > I revisited this, and I think we should stick with the original
> > > proposal of having a separate ListPartitionReassignments API. There
> > > really is no use case where the Producer or Consumer needs to know
> > > about a reassignment. They should just be notified when the set of
> > > partitions changes, which doesn't require changes to
> > > MetadataRequest/Response. The Admin client only cares if someone is
> > > managing the reassignment. So adding this state to the
> > > MetadataResponse adds overhead for no real benefit. In the common
> case
> > > where there is no ongoing reassignment, it would be 4 bytes per
> > > partition of extra overhead in the MetadataResponse.
> > >
> > > In general, I think we have a problem of oversharing in the
> > > MetadataRequest/Response. As we 10x or 100x the number of partitions
> > > we support, we'll need to get stricter about giving clients only the
> > > information they actually need, about the partitions they actually
> care
> > > about. Reassignment state clearly falls in the category of state that
> > > isn't needed by clients (except very specialized rebalancing programs).
> > >
> > > Another important consideration here is that someone managing an
> > > ongoing reassignment wants the most up-to-date information, which is
> to
> > > be found on the controller. Therefore adding this state to listTopics
> > > or describeTopics, which could contact any node in the cluster, is
> > > sub-optimal.
> > >
> > > Finally, adding this to listTopics or describeTopics feels like a
> warty
> > > API. It's an extra boolean which interacts with other extra booleans
> > > like "show internal", etc. in weird ways. I think a separate API is
> > > cleaner.
> > >
> > > >
> > > > > 3. As replicas come into sync, they will join the ISR. Will we
> await all
> > > > > target replicas joining the ISR before taking the replica out of
> the target
> > > > > replicas set? Also, I assume that target replicas can still be
> elected as
> > > > > leader?
> > > >
> > > > We'll take a replica out of the target replicas set as soon as that
> > > > replica is in the ISR. Let me clarify this in the KIP.
> > > >
> > > > > 4. Probably useful to mention permissions for the new APIs.
> > > >
> > > > Good point. I think alterPartitionAssignments should require ALTER
> on
> > > > CLUSTER. MetadataRequest permissions will be unchanged.
> > >
> > > I added permission information.
> > >
> > > best,
> > > Colin
> > >
> > > >
> > > > best,
> > > > Colin
> > > >
> > > > >
> > > > > Thanks,
> > > > > Jason
> > > > >
> > > > > On Fri, May 10, 2019 at 9:30 AM Gwen Shapira <g...@confluent.io>
> wrote:
> > > > >
> > > > > > +1 (binding)
> > > > > > Looks great, and will be awesome to have this new capability.
> > > > > >
> > > > > > On Wed, May 8, 2019 at 10:23 PM Colin McCabe <cmcc...@apache.org>
> wrote:
> > > > > >
> > > > > > > Hi all,
> > > > > > >
> > > > > > > I'd like to start the vote for KIP-455: Create an
> Administrative API for
> > > > > > > Replica Reassignment. I think this KIP is important since it
> will unlock
> > > > > > > many follow-on improvements to Kafka reassignment (see the
> "Future work"
> > > > > > > section, plus a lot of the other discussions we've had
> recently about
> > > > > > > reassignment). It also furthers the important KIP-4 goal of
> removing
> > > > > > > direct access to ZK.
> > > > > > >
> > > > > > > I made a few changes based on the discussion in the [DISCUSS]
> thread. As
> > > > > > > Robert suggested, I removed the need to explicitly cancel a
> reassignment
> > > > > > > for a partition before setting up a different reassignment for
> that
> > > > > > > specific partition. I also simplified the API a bit by adding
> a
> > > > > > > PartitionReassignment class which is used by both the alter
> and list
> > > > > > APIs.
> > > > > > >
> > > > > > > I modified the proposal so that we now deprecate the old
> znode-based API
> > > > > > > rather than removing it completely. That should give external
> > > > > > rebalancing
> > > > > > > tools some time to transition to the new API.
> > > > > > >
> > > > > > > To clarify a question Viktor asked, I added a note that the
> > > > > > > kafka-reassign-partitions.sh will now use a --bootstrap-server
> argument
> > > > > > to
> > > > > > > contact the admin APIs.
> > > > > > >
> > > > > > > thanks,
> > > > > > > Colin
> > > > > > >
> > > > > >
> > > > > >
> > > > > > --
> > > > > > *Gwen Shapira*
> > > > > > Product Manager | Confluent
> > > > > > 650.450.2760 | @gwenshap
> > > > > > Follow us: Twitter <https://twitter.com/ConfluentInc> | blog
> > > > > > <http://www.confluent.io/blog>
> > > > > >
> > > > >
> > > >
> > >
>
