Yeah, I think adding this information to LeaderAndIsr makes sense.  It would be 
better to track "reassigningReplicas" than "originalReplicas", I think.  
Tracking "originalReplicas" is going to involve sending a lot more data, since 
most replicas in the system are not reassigning at any given point.  Or we 
would need a hack in the RPC like null = no replicas are reassigning.

On a related note, what do you think about the idea of storing the reassigning 
replicas in  /brokers/topics/[topic]/partitions/[partitionId]/state, rather 
than in the reassignment znode?  I don't think this requires a major change to 
the proposal-- when the controller becomes aware that it should do a 
reassignment, the controller could make the changes.  This also helps keep the 
reassignment znode from getting larger, which has been a problem.

best,
Colin


On Mon, Apr 8, 2019, at 09:29, Jason Gustafson wrote:
> Hey George,
> 
> For the URP during a reassignment,  if the "original_replicas" is kept for
> > the current pending reassignment. I think it will be very easy to compare
> > that with the topic/partition's ISR.  If all "original_replicas" are in
> > ISR, then URP should be 0 for that topic/partition.
> 
> 
> Yeah, that makes sense. But I guess we would need "original_replicas" to be
> propagated to partition leaders in the LeaderAndIsr request since leaders
> are the ones that are computing URPs. That is basically what KIP-352 had
> proposed, but we also need the changes to the reassignment path. Perhaps it
> makes more sense to address this problem in KIP-236 since that is where you
> have already introduced "original_replicas"? I'm also happy to do KIP-352
> as a follow-up to KIP-236.
> 
> Best,
> Jason
> 
> 
> On Sun, Apr 7, 2019 at 5:09 PM Ismael Juma <isma...@gmail.com> wrote:
> 
> > Good discussion about where we should do batching. I think if there is a
> > clear great way to batch, then it makes a lot of sense to just do it once.
> > However, if we think there is scope for experimenting with different
> > approaches, then an API that tools can use makes a lot of sense. They can
> > experiment and innovate. Eventually, we can integrate something into Kafka
> > if it makes sense.
> >
> > Ismael
> >
> > On Sun, Apr 7, 2019, 11:03 PM Colin McCabe <cmcc...@apache.org> wrote:
> >
> > > Hi George,
> > >
> > > As Jason was saying, it seems like there are two directions we could go
> > > here: an external system handling batching, and the controller handling
> > > batching.  I think the controller handling batching would be better,
> > since
> > > the controller has more information about the state of the system.  If
> > the
> > > controller handles batching, then the controller could also handle things
> > > like setting up replication quotas for individual partitions.  The
> > > controller could do things like throttle replication down if the cluster
> > > was having problems.
> > >
> > > We kind of need to figure out which way we're going to go on this one
> > > before we set up big new APIs, I think.  If we want an external system to
> > > handle batching, then we can keep the idea that there is only one
> > > reassignment in progress at once.  If we want the controller to handle
> > > batching, we will need to get away from that idea.  Instead, we should
> > just
> > > have a bunch of "ideal assignments" that we tell the controller about,
> > and
> > > let it decide how to do the batching.  These ideal assignments could
> > change
> > > continuously over time, so from the admin's point of view, there would be
> > > no start/stop/cancel, but just individual partition reassignments that we
> > > submit, perhaps over a long period of time.  And then cancellation might
> > > just mean cancelling just that individual partition reassignment, not all
> > > partition reassignments.
> > >
> > > best,
> > > Colin
> > >
> > > On Fri, Apr 5, 2019, at 19:34, George Li wrote:
> > > >  Hi Jason / Viktor,
> > > >
> > > > For the URP during a reassignment,  if the "original_replicas" is kept
> > > > for the current pending reassignment. I think it will be very easy to
> > > > compare that with the topic/partition's ISR.  If all
> > > > "original_replicas" are in ISR, then URP should be 0 for that
> > > > topic/partition.
> > > >
> > > > It would be also nice to separate the metrics MaxLag/TotalLag for
> > > > Reassignments. I think that will also require "original_replicas" (the
> > > > topic/partition's replicas just before reassignment when the AR
> > > > (Assigned Replicas) is set to Set(original_replicas) +
> > > > Set(new_replicas_in_reassign_partitions) ).
> > > >
> > > > Thanks,
> > > > George
> > > >
> > > >     On Friday, April 5, 2019, 6:29:55 PM PDT, Jason Gustafson
> > > > <ja...@confluent.io> wrote:
> > > >
> > > >  Hi Viktor,
> > > >
> > > > Thanks for writing this up. As far as questions about overlap with
> > > KIP-236,
> > > > I agree it seems mostly orthogonal. I think KIP-236 may have had a
> > larger
> > > > initial scope, but now it focuses on cancellation and batching is left
> > > for
> > > > future work.
> > > >
> > > > With that said, I think we may not actually need a KIP for the current
> > > > proposal since it doesn't change any APIs. To make it more generally
> > > > useful, however, it would be nice to handle batching at the partition
> > > level
> > > > as well as Jun suggests. The basic question is at what level should the
> > > > batching be determined. You could rely on external processes (e.g.
> > cruise
> > > > control) or it could be built into the controller. There are tradeoffs
> > > > either way, but I think it simplifies such tools if it is handled
> > > > internally. Then it would be much safer to submit a larger reassignment
> > > > even just using the simple tools that come with Kafka.
> > > >
> > > > By the way, since you are looking into some of the reassignment logic,
> > > > another problem that we might want to address is the misleading way we
> > > > report URPs during a reassignment. I had a naive proposal for this
> > > > previously, but it didn't really work
> > > >
> > >
> > https://cwiki.apache.org/confluence/display/KAFKA/KIP-352%3A+Distinguish+URPs+caused+by+reassignment
> > > .
> > > > Potentially fixing that could fall under this work as well if you think
> > > > it
> > > > makes sense.
> > > >
> > > > Best,
> > > > Jason
> > > >
> > > > On Thu, Apr 4, 2019 at 4:49 PM Jun Rao <j...@confluent.io> wrote:
> > > >
> > > > > Hi, Viktor,
> > > > >
> > > > > Thanks for the KIP. A couple of comments below.
> > > > >
> > > > > 1. Another potential thing to do reassignment incrementally is to
> > move
> > > a
> > > > > batch of partitions at a time, instead of all partitions. This may
> > > lead to
> > > > > less data replication since by the time the first batch of partitions
> > > have
> > > > > been completely moved, some data of the next batch may have been
> > > deleted
> > > > > due to retention and doesn't need to be replicated.
> > > > >
> > > > > 2. "Update CR in Zookeeper with TR for the given partition". Which ZK
> > > path
> > > > > is this for?
> > > > >
> > > > > Jun
> > > > >
> > > > > On Sat, Feb 23, 2019 at 2:12 AM Viktor Somogyi-Vass <
> > > > > viktorsomo...@gmail.com>
> > > > > wrote:
> > > > >
> > > > > > Hi Harsha,
> > > > > >
> > > > > > As far as I understand KIP-236 it's about enabling reassignment
> > > > > > cancellation and as a future plan providing a queue of replica
> > > > > reassignment
> > > > > > steps to allow manual reassignment chains. While I agree that the
> > > > > > reassignment chain has a specific use case that allows fine grain
> > > control
> > > > > > over reassignment process, My proposal on the other hand doesn't
> > talk
> > > > > about
> > > > > > cancellation but it only provides an automatic way to
> > incrementalize
> > > an
> > > > > > arbitrary reassignment which I think fits the general use case
> > where
> > > > > users
> > > > > > don't want that level of control but still would like a balanced
> > way
> > > of
> > > > > > reassignments. Therefore I think it's still relevant as an
> > > improvement of
> > > > > > the current algorithm.
> > > > > > Nevertheless I'm happy to add my ideas to KIP-236 as I think it
> > > would be
> > > > > a
> > > > > > great improvement to Kafka.
> > > > > >
> > > > > > Cheers,
> > > > > > Viktor
> > > > > >
> > > > > > On Fri, Feb 22, 2019 at 5:05 PM Harsha <ka...@harsha.io> wrote:
> > > > > >
> > > > > > > Hi Viktor,
> > > > > > >            There is already KIP-236 for the same feature and
> > George
> > > > > made
> > > > > > > a PR for this as well.
> > > > > > > Lets consolidate these two discussions. If you have any cases
> > that
> > > are
> > > > > > not
> > > > > > > being solved by KIP-236 can you please mention them in that
> > > thread. We
> > > > > > can
> > > > > > > address as part of KIP-236.
> > > > > > >
> > > > > > > Thanks,
> > > > > > > Harsha
> > > > > > >
> > > > > > > On Fri, Feb 22, 2019, at 5:44 AM, Viktor Somogyi-Vass wrote:
> > > > > > > > Hi Folks,
> > > > > > > >
> > > > > > > > I've created a KIP about an improvement of the reassignment
> > > algorithm
> > > > > > we
> > > > > > > > have. It aims to enable partition-wise incremental
> > reassignment.
> > > The
> > > > > > > > motivation for this is to avoid excess load that the current
> > > > > > replication
> > > > > > > > algorithm implicitly carries as in that case there are points
> > in
> > > the
> > > > > > > > algorithm where both the new and old replica set could be
> > online
> > > and
> > > > > > > > replicating which puts double (or almost double) pressure on
> > the
> > > > > > brokers
> > > > > > > > which could cause problems.
> > > > > > > > Instead my proposal would slice this up into several steps
> > where
> > > each
> > > > > > > step
> > > > > > > > is calculated based on the final target replicas and the
> > current
> > > > > > replica
> > > > > > > > assignment taking into account scenarios where brokers could be
> > > > > offline
> > > > > > > and
> > > > > > > > when there are not enough replicas to fulfil the
> > > min.insync.replica
> > > > > > > > requirement.
> > > > > > > >
> > > > > > > > The link to the KIP:
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > >
> > https://cwiki.apache.org/confluence/display/KAFKA/KIP-435%3A+Incremental+Partition+Reassignment
> > > > > > > >
> > > > > > > > I'd be happy to receive any feedback.
> > > > > > > >
> > > > > > > > An important note is that this KIP and another one, KIP-236
> > that
> > > is
> > > > > > > > about
> > > > > > > > interruptible reassignment (
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > >
> > https://cwiki.apache.org/confluence/display/KAFKA/KIP-236%3A+Interruptible+Partition+Reassignment
> > > > > > > )
> > > > > > > > should be compatible.
> > > > > > > >
> > > > > > > > Thanks,
> > > > > > > > Viktor
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

Reply via email to