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From George Li <sql_consult...@yahoo.com.INVALID>
Subject Re: [DISCUSS] KIP-236 Interruptible Partition Reassignment
Date Wed, 20 Feb 2019 20:16:31 GMT
Hi,
After discussing with Tom, Harsha and I are picking up KIP-236.  The work focused on safely/cleanly cancel / rollback pending reassignments in a timely fashion.  Pull Request #6296  Still working on more integration/system tests. 
Please review and provide feedbacks/suggestions. 
Thanks,George

On Saturday, December 23, 2017, 0:51:13 GMT, Jun Rao <jun@confluent.io> wrote:

Hi, Tom,

Thanks for the reply.

10. That's a good thought. Perhaps it's better to get rid of
/admin/reassignment_requests
too. The window when a controller is not available is small. So, we can
just failed the admin client if the controller is not reachable after the
timeout.

13. With the changes in 10, the old approach is handled through ZK callback
and the new approach is through Kafka RPC. The ordering between the two is
kind of arbitrary. Perhaps the ordering can just be based on the order that
the reassignment is added to the controller request queue. From there, we
can either do the overriding or the prevention.

Jun


On Fri, Dec 22, 2017 at 7:31 AM, Tom Bentley <t.j.bentley@gmail.com> wrote:

> Hi Jun,
>
> Thanks for responding, my replies are inline:
>
> 10. You explanation makes sense. My remaining concern is the additional ZK
> > writes in the proposal. With the proposal, we will need to do following
> > writes in ZK.
> >
> > a. write new assignment in /admin/reassignment_requests
> >
> > b. write new assignment and additional metadata in
> > /admin/reassignments/$topic/$partition
> >
> > c. write old + new assignment  in /brokers/topics/[topic]
> >
> > d. write new assignment in /brokers/topics/[topic]
> >
> > e. delete /admin/reassignments/$topic/$partition
> >
> > So, there are quite a few ZK writes. I am wondering if it's better to
> > consolidate the info in /admin/reassignments/$topic/$partition into
> > /brokers/topics/[topic].
> > For example, we can just add some new JSON fields in
> > /brokers/topics/[topic]
> > to remember the new assignment and potentially the original replica count
> > when doing step c. Those fields with then be removed in step d. That way,
> > we can get rid of step b and e, saving 2 ZK writes per partition.
> >
>
> This seems like a great idea to me.
>
> It might also be possible to get rid of the /admin/reassignment_requests
> subtree too. I've not yet published the ideas I have for the AdminClient
> API for reassigning partitions, but given the existence of such an API, the
> route to starting a reassignment would be the AdminClient, and not
> zookeeper. In that case there is no need for /admin/reassignment_requests
> at all. The only drawback that I can see is that while it's currently
> possible to trigger a reassignment even during a controller
> election/failover that would no longer be the case if all requests had to
> go via the controller.
>
>
> > 11. What you described sounds good. We could potentially optimize the
> > dropped replicas a bit more. Suppose that assignment [0,1,2] is first
> > changed to [1,2,3] and then to [2,3,4]. When initiating the second
> > assignment, we may end up dropping replica 3 and only to restart it
> again.
> > In this case, we could only drop a replica if it's not going to be added
> > back again.
> >
>
> I had missed that, thank you! I will update the proposed algorithm to
> prevent this.
>
>
> > 13. Since this is a corner case, we can either prevent or allow
> overriding
> > with old/new mechanisms. To me, it seems that allowing is simpler to
> > implement, the order in /admin/reassignment_requests determines the
> > ordering the of override, whether that's initiated by the new way or the
> > old way.
> >
>
> That makes sense except for the corner case where:
>
> * There is no current controller and
> * Writes to both the new and old znodes happen
>
> On election of the new controller, for those partitions with both a
> reassignment_request and in /admin/reassign_partitions, we have to decide
> which should win. You could use the modification time, though there are
> some very unlikely scenarios where that doesn't work properly, for example
> if both znodes have the same mtime, or the /admin/reassign_partitions was
> updated, but the assignment of the partition wasn't changed, like this:
>
> 0. /admin/reassign_partitions has my-topic/42 = [1,2,3]
> 1. Controller stops watching.
> 2. Create /admin/reassignment_requests/request_1234 to change the
> reassignment of partition my-topic/42 = [4,5,6]
> 3. Update /admin/reassign_partitions to add your-topic/12=[7,8,9]
> 4. New controller resumes
>
>
>
> > Thanks,
> >
> > Jun
> >
> > On Tue, Dec 19, 2017 at 2:43 AM, Tom Bentley <t.j.bentley@gmail.com>
> > wrote:
> >
> > > Hi Jun,
> > >
> > > 10. Another concern of mine is on consistency with the current pattern.
> > The
> > > > current pattern for change notification based on ZK is (1) we first
> > write
> > > > the actual value in the entity path and then write the change
> > > notification
> > > > path, and (2)  the change notification path only includes what entity
> > has
> > > > changed but not the actual changes. If we want to follow this pattern
> > for
> > > > consistency, /admin/reassignment_requests/request_xxx will only have
> > the
> > > > partitions whose reassignment have changed, but not the actual
> > > > reassignment.
> > > >
> > >
> > > Ah, I hadn't understood part (2). That means my concern about
> efficiency
> > > with the current pattern is misplaced. There are still some interesting
> > > differences in semantics, however:
> > >
> > > a) The mechanism currently proposed in KIP-236 means that the
> controller
> > is
> > > the only writer to /admin/reassignments. This means it can include
> > > information in these znodes that requesters might not know, or
> > information
> > > that's necessary to perform the reassignment but not necessary to
> > describe
> > > the request. While this could be handled using the current pattern it
> > would
> > > rely on all  writers to preserve any information added by the
> controller,
> > > which seems complicated and hence fragile.
> > >
> > > b) The current pattern for change notification doesn't cope with
> > competing
> > > writers to the entity path: If two processes write to the entity path
> > > before the controller can read it (due to notification) then one set of
> > > updates will be lost.
> > >
> > > c) If a single writing process crashes after writing to the entity
> path,
> > > but before writing to the notification path then the write will be
> lost.
> > >
> > > I'm actually using point a) in my WIP (see below). Points b) and c) are
> > > obviously edge cases.
> > >
> > >
> > > > 11. Ok. I am not sure that I fully understand the description of that
> > > part.
> > > > Does "assigned" refer to the current assignment? Could you also
> > describe
> > > > where the length of the original assignment is stored in ZK?
> > > >
> > >
> > > Sorry if the description is not clear. Yes, "assigned" referrs to the
> > > currently assigned replicas (taken from the
> > > ControllerContext.partitionReplicaAssignment). I would store the
> length
> > of
> > > the original assignment in the /admin/reassignments/$topic/$partition
> > > znode
> > > (this is where the point (a) above is useful -- the requester shouldn't
> > > know that this information is used by the controller).
> > >
> > > I've updated the KIP to make these points clearer.
> > >
> > >
> > > > 13. Hmm, I am not sure that the cancellation needs to be done for the
> > > whole
> > > > batch. The reason that I brought this up is for consistency. The KIP
> > > allows
> > > > override when using the new approach. It just seems that it's simpler
> > to
> > > > extend this model when resolving multiple changes between the old and
> > the
> > > > new approach.
> > >
> > >
> > > Ah, I think I've been unclear on this point too. Currently the
> > > ReassignPartitionsCommand enforces that you can't change reassignments,
> > but
> > > this doesn't stop other ZK clients making changes to
> > > /admin/reassign_partitions directly and I believe some Kafka users do
> > > indeed change reassignments in-flight by writing to
> > > /admin/reassign_partitions. What I'm proposing doesn't break that at
> all.
> > > The semantic I've implemented is only that the controller only refuses
> a
> > > reassignment change if there is already one in-flight (i.e. in
> > > /admin/reassignments/$topic/$partition) **via the other mechansim**.
> So
> > if
> > > you're using /admin/reassign_partitions and you change or cancel part
> of
> > it
> > > via /admin/reassign_partitions, that's OK. Likewise if you're using
> > > /admin/reassignment_request/request_xxx and you change or cancel part
> of
> > > it
> > > via another /admin/reassignment_request/request_xxx, that's OK.What
> you
> > > can't do is change a request that was started via
> > > /admin/reassign_partitions via /admin/reassignment_request/
> request_xxx,
> > or
> > > vice versa.
> > >
> > > What I was thinking of when I replied is the case where, on controller
> > > failover, /admin/reassign_partitions has been changed and
> > > /admin/reassignment_request/request_xxx created (in the period when
> the
> > > new
> > > controller was being elected, for example) with a common partition. In
> > this
> > > case we should apply a consistent rule to that used when the
> notification
> > > happen in real time. Your suggestion to use the modification time of
> the
> > > znode would work here too (except in the edge case where ZK writes to
> > both
> > > znodes happen within the same clock tick on the ZK server, so the
> mtimes
> > > are the same).
> > >
> > > Let me know if you think this is the right semantic and I'll try to
> > clarify
> > > the KIP.
> > >
> > > Many thanks,
> > >
> > > Tom
> > >
> > > On 18 December 2017 at 18:12, Jun Rao <jun@confluent.io> wrote:
> > >
> > > > Hi, Tom,
> > > >
> > > > Thanks for the reply. A few more followup comments below.
> > > >
> > > > 10. Another concern of mine is on consistency with the current
> pattern.
> > > The
> > > > current pattern for change notification based on ZK is (1) we first
> > write
> > > > the actual value in the entity path and then write the change
> > > notification
> > > > path, and (2)  the change notification path only includes what entity
> > has
> > > > changed but not the actual changes. If we want to follow this pattern
> > for
> > > > consistency, /admin/reassignment_requests/request_xxx will only have
> > the
> > > > partitions whose reassignment have changed, but not the actual
> > > > reassignment.
> > > >
> > > > 11. Ok. I am not sure that I fully understand the description of that
> > > part.
> > > > Does "assigned" refer to the current assignment? Could you also
> > describe
> > > > where the length of the original assignment is stored in ZK?
> > > >
> > > > 13. Hmm, I am not sure that the cancellation needs to be done for the
> > > whole
> > > > batch. The reason that I brought this up is for consistency. The KIP
> > > allows
> > > > override when using the new approach. It just seems that it's simpler
> > to
> > > > extend this model when resolving multiple changes between the old and
> > the
> > > > new approach.
> > > >
> > > > Jun
> > > >
> > > >
> > > >
> > > > On Mon, Dec 18, 2017 at 2:45 AM, Tom Bentley <t.j.bentley@gmail.com>
> > > > wrote:
> > > >
> > > > > Hi Jun,
> > > > >
> > > > > Thanks for replying, some answers below:
> > > > >
> > > > >
> > > > > > 10. The proposal now stores the reassignment for all partitions
> in
> > > > > > /admin/reassignment_requests/request_xxx. If the number of
> > > reassigned
> > > > > > partitions is larger, the ZK write may hit the default 1MB limit
> > and
> > > > > fail.
> > > > > > An alternative approach is to have the reassignment requester
> first
> > > > write
> > > > > > the new assignment for each partition under
> > > > > > /admin/reassignments/$topic/$partition and then write
> > > > > > /admin/reassignment_requests/request_xxx with an empty value.
> The
> > > > > > controller can then read all values under /admin/reassignments.
> > > > > >
> > > > >
> > > > > You're right that reassigning enough partitions would hit the 1MB
> > > limit,
> > > > > but I don't think this would be a problem in practice because it
> > would
> > > be
> > > > > trivial to split the partitions into several requests (i.e.
> mutleiple
> > > > > request_xxx).
> > > > > I don't think the non-atomicity this would imply is a problem. By
> > > writing
> > > > > the partitions whose /admin/reassignments/$topic/$partition has
> been
> > > > > created or changed it makes it much more efficient to know which of
> > > those
> > > > > znodes we need to read. If I understand your suggestion, you would
> > have
> > > > to
> > > > > read every node under /admin/reassignments to figure out which had
> > > > changed.
> > > > >
> > > > >
> > > > > > 11. The improvement you suggested in onPartitionReassignment()
> > sounds
> > > > > good
> > > > > > at the high level. The computation of those dropped partitions
> > seems
> > > a
> > > > > bit
> > > > > > complicated. Perhaps a simple approach is to drop the replicas
> not
> > in
> > > > the
> > > > > > original assignment and newest reassignment?
> > > > > >
> > > > >
> > > > > This was what I came up with originally too, but when I looked into
> > > > > implementing it I found a couple of things which made me reconsider
> > it.
> > > > > Consider the reassignments [0,1] -> [2,3] -> [3,4]. In words: we
> > start
> > > > > reassigning to [2,3], but then change our minds about 2 and switch
> it
> > > to
> > > > 4
> > > > > (maybe we've figured out a better overall balance). At that point
> it
> > is
> > > > > perfectly possible that broker 2 is in-sync and broker 1 is not
> > > in-sync.
> > > > It
> > > > > seems silly to drop broker 2 in favour of broker 1: We're
> needlessly
> > > > giving
> > > > > the cluster more work to do.
> > > > >
> > > > > The second thing that made me reconsider was in that same scenario
> > it's
> > > > > even possible that broker 2 is the leader of the partition.
> Obviously
> > > we
> > > > > can elect a new leader before dropping it, but not without causing
> > > > > disruption to producers and consumers.
> > > > >
> > > > > By accepting a little more complexity in choosing which brokers to
> > drop
> > > > we
> > > > > make the dropping simpler (no need for leader election) and ensure
> > the
> > > > > cluster has less work to do.
> > > > >
> > > > >
> > > > > > 12. You brought up the need of remembering the original
> assignment.
> > > > This
> > > > > > will be lost if the assignment is changed multiple times if we
> > follow
> > > > the
> > > > > > approach described in 10. One way is to store the original
> > assignment
> > > > in
> > > > > > /brokers/topics/[topic] as the following. When the final
> > reassignment
> > > > > > completes, we can remove the original field.
> > > > > > {
> > > > > >   "version": 1,
> > > > > >   "partitions": {"0": [0, 1, 3] },
> > > > > >   "originals": {"0": [0, 1, 2] }
> > > > > > }
> > > > > >
> > > > >
> > > > > While I was implementing my first version of
> > onPartitionReassignment(),
> > > > > where I preferred the originals, I was storing the originals in the
> > > > > /admin/reassignments/$topic/$partition znodes. Since we will
> remove
> > > that
> > > > > znode at the end of reassignment anyway, I would suggest this is a
> > > better
> > > > > place to store that data (if it's necessary to do so), so that we
> can
> > > > avoid
> > > > > another ZK round trip.
> > > > >
> > > > >
> > > > > > 13. For resolving the conflict between /admin/reassign_partitions
> > and
> > > > > > /admin/reassignments/$topic/$partition, perhaps it's more
> natural
> > to
> > > > > just
> > > > > > let the assignment with a newer timestamp to override the older
> > one?
> > > > > >
> > > > >
> > > > > That would work but with slightly different semantics to what I
> have:
> > > > Since
> > > > > /admin/reassign_partitions contains multiple partitions, using the
> > > > > timestamp means the whole batch wins or losses. By tracking how
> each
> > > > > request was made we can be more fine-grained. I'm to use the
> > > modification
> > > > > time if such granularity is not required.
> > > > >
> > > > >
> > > > > > 14. Implementation wise, currently, we register a watcher of the
> > isr
> > > > path
> > > > > > of each partition being reassigned. This has the potential issue
> of
> > > > > > registering many listeners. An improvement could be just
> > piggybacking
> > > > on
> > > > > > the existing IsrChangeNotificationHandler, which only watches a
> > > single
> > > > ZK
> > > > > > path and is triggered on a batch of isr changes. This is kind of
> > > > > orthogonal
> > > > > > to the KIP. However, if we are touching the reassignment logic,
> it
> > > may
> > > > be
> > > > > > worth considering.
> > > > >
> > > > >
> > > > > Let me look into that.
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Tom
> > > > >
> > > > > On 16 December 2017 at 02:19, Jun Rao <jun@confluent.io> wrote:
> > > > >
> > > > > > Hi, Tom,
> > > > > >
> > > > > > Thanks for the updated KIP. A few more comments below.
> > > > > >
> > > > > > 10. The proposal now stores the reassignment for all partitions
> in
> > > > > > /admin/reassignment_requests/request_xxx. If the number of
> > > reassigned
> > > > > > partitions is larger, the ZK write may hit the default 1MB limit
> > and
> > > > > fail.
> > > > > > An alternative approach is to have the reassignment requester
> first
> > > > write
> > > > > > the new assignment for each partition under
> > > > > > /admin/reassignments/$topic/$partition and then write
> > > > > > /admin/reassignment_requests/request_xxx with an empty value.
> The
> > > > > > controller can then read all values under /admin/reassignments.
> > > > > >
> > > > > > 11. The improvement you suggested in onPartitionReassignment()
> > sounds
> > > > > good
> > > > > > at the high level. The computation of those dropped partitions
> > seems
> > > a
> > > > > bit
> > > > > > complicated. Perhaps a simple approach is to drop the replicas
> not
> > in
> > > > the
> > > > > > original assignment and newest reassignment?
> > > > > >
> > > > > > 12. You brought up the need of remembering the original
> assignment.
> > > > This
> > > > > > will be lost if the assignment is changed multiple times if we
> > follow
> > > > the
> > > > > > approach described in 10. One way is to store the original
> > assignment
> > > > in
> > > > > > /brokers/topics/[topic] as the following. When the final
> > reassignment
> > > > > > completes, we can remove the original field.
> > > > > > {
> > > > > >   "version": 1,
> > > > > >   "partitions": {"0": [0, 1, 3] },
> > > > > >   "originals": {"0": [0, 1, 2] }
> > > > > > }
> > > > > >
> > > > > > 13. For resolving the conflict between /admin/reassign_partitions
> > and
> > > > > > /admin/reassignments/$topic/$partition, perhaps it's more
> natural
> > to
> > > > > just
> > > > > > let the assignment with a newer timestamp to override the older
> > one?
> > > > > >
> > > > > > 14. Implementation wise, currently, we register a watcher of the
> > isr
> > > > path
> > > > > > of each partition being reassigned. This has the potential issue
> of
> > > > > > registering many listeners. An improvement could be just
> > piggybacking
> > > > on
> > > > > > the existing IsrChangeNotificationHandler, which only watches a
> > > single
> > > > ZK
> > > > > > path and is triggered on a batch of isr changes. This is kind of
> > > > > orthogonal
> > > > > > to the KIP. However, if we are touching the reassignment logic,
> it
> > > may
> > > > be
> > > > > > worth considering.
> > > > > >
> > > > > > Thanks,
> > > > > >
> > > > > > Jun
> > > > > >
> > > > > > On Fri, Dec 15, 2017 at 10:17 AM, Tom Bentley <
> > t.j.bentley@gmail.com
> > > >
> > > > > > wrote:
> > > > > >
> > > > > > > Just wanted to mention that I've started KIP-240, which builds
> on
> > > top
> > > > > of
> > > > > > > this one to provide an AdminClient API for listing and
> describing
> > > > > > > reassignments.
> > > > > > >
> > > > > > > On 15 December 2017 at 14:34, Tom Bentley <
> t.j.bentley@gmail.com
> > >
> > > > > wrote:
> > > > > > >
> > > > > > > > > Should we seek to improve this algorithm in this KIP, or
> > leave
> > > > that
> > > > > > as
> > > > > > > > a later optimisation?
> > > > > > > >
> > > > > > > > I've updated the KIP with a proposed algorithm.
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > On 14 December 2017 at 09:57, Tom Bentley <
> > t.j.bentley@gmail.com
> > > >
> > > > > > wrote:
> > > > > > > >
> > > > > > > >> Thanks Ted, now fixed.
> > > > > > > >>
> > > > > > > >> On 13 December 2017 at 18:38, Ted Yu <yuzhihong@gmail.com>
> > > wrote:
> > > > > > > >>
> > > > > > > >>> Tom:
> > > > > > > >>> bq. create a znode /admin/reassignments/$topic-$partition
> > > > > > > >>>
> > > > > > > >>> Looks like the tree structure above should be:
> > > > > > > >>>
> > > > > > > >>> /admin/reassignments/$topic/$partition
> > > > > > > >>>
> > > > > > > >>> bq. The controller removes /admin/reassignment/$topic/$
> > > partition
> > > > > > > >>>
> > > > > > > >>> Note the lack of 's' for reassignment. It would be good to
> > make
> > > > > > > zookeeper
> > > > > > > >>> paths consistent.
> > > > > > > >>>
> > > > > > > >>> Thanks
> > > > > > > >>>
> > > > > > > >>> On Wed, Dec 13, 2017 at 9:49 AM, Tom Bentley <
> > > > > t.j.bentley@gmail.com>
> > > > > > > >>> wrote:
> > > > > > > >>>
> > > > > > > >>> > Hi Jun and Ted,
> > > > > > > >>> >
> > > > > > > >>> > Jun, you're right that needing one watcher per reassigned
> > > > > partition
> > > > > > > >>> > presents a scalability problem, and using a separate
> > > > notification
> > > > > > > path
> > > > > > > >>> > solves that. I also agree that it makes sense to prevent
> > > users
> > > > > from
> > > > > > > >>> using
> > > > > > > >>> > both methods on the same reassignment.
> > > > > > > >>> >
> > > > > > > >>> > Ted, naming the reassignments like mytopic-42 was simpler
> > > > while I
> > > > > > was
> > > > > > > >>> > proposing a watcher-per-reassignment (I'd have needed a
> > child
> > > > > > watcher
> > > > > > > >>> on
> > > > > > > >>> > /admin/reassignments and also on
> > > /admin/reassignments/mytopic).
> > > > > > Using
> > > > > > > >>> the
> > > > > > > >>> > separate notification path means I don't need any
> watchers
> > in
> > > > the
> > > > > > > >>> > /admin/reassignments subtree, so switching to
> > > > > > > >>> /admin/reassignments/mytopic/
> > > > > > > >>> > 42
> > > > > > > >>> > would work, and avoid /admin/reassignments having a very
> > > large
> > > > > > number
> > > > > > > >>> of
> > > > > > > >>> > child nodes. On the other hand it also means I have to
> > create
> > > > and
> > > > > > > >>> delete
> > > > > > > >>> > the topic nodes (e.g. /admin/reassignments/mytopic),
> which
> > > > incurs
> > > > > > the
> > > > > > > >>> cost
> > > > > > > >>> > of extra round trips to zookeeper. I suppose that since
> > > > > > reassignment
> > > > > > > is
> > > > > > > >>> > generally a slow process it makes little difference if we
> > > > > increase
> > > > > > > the
> > > > > > > >>> > latency of the interactions with zookeeper.
> > > > > > > >>> >
> > > > > > > >>> > I have updated the KIP with these improvements, and a
> more
> > > > > detailed
> > > > > > > >>> > description of exactly how we would manage these znodes.
> > > > > > > >>> >
> > > > > > > >>> > Reading the algorithm in KafkaController.
> > > > > > onPartitionReassignment(),
> > > > > > > it
> > > > > > > >>> > seems that it would be suboptimal for changing
> > reassignments
> > > > > > > in-flight.
> > > > > > > >>> > Consider an initial assignment of [1,2], reassigned to
> > [2,3]
> > > > and
> > > > > > then
> > > > > > > >>> > changed to [2,4]. Broker 3 will remain in the assigned
> > > replicas
> > > > > > until
> > > > > > > >>> > broker 4 is in sync, even though 3 wasn't actually one of
> > the
> > > > > > > original
> > > > > > > >>> > assigned replicas and is no longer a new assigned
> replica.
> > I
> > > > > think
> > > > > > > this
> > > > > > > >>> > also affects the case where the reassignment is cancelled
> > > > > > > >>> > ([1,2]->[2,3]->[1,2]): We again have to wait for 3 to
> catch
> > > up,
> > > > > > even
> > > > > > > >>> though
> > > > > > > >>> > its replica will then be deleted.
> > > > > > > >>> >
> > > > > > > >>> > Should we seek to improve this algorithm in this KIP, or
> > > leave
> > > > > that
> > > > > > > as
> > > > > > > >>> a
> > > > > > > >>> > later optimisation?
> > > > > > > >>> >
> > > > > > > >>> > Cheers,
> > > > > > > >>> >
> > > > > > > >>> > Tom
> > > > > > > >>> >
> > > > > > > >>> > On 11 December 2017 at 21:31, Jun Rao <jun@confluent.io>
> > > > wrote:
> > > > > > > >>> >
> > > > > > > >>> > > Another question is on the compatibility. Since now
> there
> > > > are 2
> > > > > > > ways
> > > > > > > >>> of
> > > > > > > >>> > > specifying a partition reassignment, one under
> > > > > > > >>> /admin/reassign_partitions
> > > > > > > >>> > > and the other under /admin/reassignments, we probably
> > want
> > > to
> > > > > > > >>> prevent the
> > > > > > > >>> > > same topic being reassigned under both paths at the
> same
> > > > time?
> > > > > > > >>> > > Thanks,
> > > > > > > >>> > >
> > > > > > > >>> > > Jun
> > > > > > > >>> > >
> > > > > > > >>> > >
> > > > > > > >>> > >
> > > > > > > >>> > > On Fri, Dec 8, 2017 at 5:41 PM, Jun Rao <
> > jun@confluent.io>
> > > > > > wrote:
> > > > > > > >>> > >
> > > > > > > >>> > > > Hi, Tom,
> > > > > > > >>> > > >
> > > > > > > >>> > > > Thanks for the KIP. It definitely addresses one of
> the
> > > pain
> > > > > > > points
> > > > > > > >>> in
> > > > > > > >>> > > > partition reassignment. Another issue that it also
> > > > addresses
> > > > > is
> > > > > > > >>> the ZK
> > > > > > > >>> > > node
> > > > > > > >>> > > > size limit when writing the reassignment JSON.
> > > > > > > >>> > > >
> > > > > > > >>> > > > My only concern is that the KIP needs to create one
> > > watcher
> > > > > per
> > > > > > > >>> > > reassigned
> > > > > > > >>> > > > partition. This could add overhead in ZK and
> complexity
> > > for
> > > > > > > >>> debugging
> > > > > > > >>> > > when
> > > > > > > >>> > > > lots of partitions are being reassigned
> simultaneously.
> > > We
> > > > > > could
> > > > > > > >>> > > > potentially improve this by introducing a separate ZK
> > > path
> > > > > for
> > > > > > > >>> change
> > > > > > > >>> > > > notification as we do for configs. For example, every
> > > time
> > > > we
> > > > > > > >>> change
> > > > > > > >>> > the
> > > > > > > >>> > > > assignment for a set of partitions, we could further
> > > write
> > > > a
> > > > > > > >>> sequential
> > > > > > > >>> > > > node /admin/reassignment_changes/[change_x]. That
> way,
> > > the
> > > > > > > >>> controller
> > > > > > > >>> > > > only needs to watch the change path. Once a change is
> > > > > > triggered,
> > > > > > > >>> the
> > > > > > > >>> > > > controller can read everything under
> > > /admin/reassignments/.
> > > > > > > >>> > > >
> > > > > > > >>> > > > Jun
> > > > > > > >>> > > >
> > > > > > > >>> > > >
> > > > > > > >>> > > > On Wed, Dec 6, 2017 at 1:19 PM, Tom Bentley <
> > > > > > > t.j.bentley@gmail.com
> > > > > > > >>> >
> > > > > > > >>> > > wrote:
> > > > > > > >>> > > >
> > > > > > > >>> > > >> Hi,
> > > > > > > >>> > > >>
> > > > > > > >>> > > >> This is still very new, but I wanted some quick
> > feedback
> > > > on
> > > > > a
> > > > > > > >>> > > preliminary
> > > > > > > >>> > > >> KIP which could, I think, help with providing an
> > > > AdminClient
> > > > > > API
> > > > > > > >>> for
> > > > > > > >>> > > >> partition reassignment.
> > > > > > > >>> > > >>
> > > > > > > >>> > > >> https://cwiki.apache.org/
> > confluence/display/KAFKA/KIP-
> > > > 236%
> > > > > > > >>> > > >> 3A+Interruptible+Partition+Reassignment
> > > > > > > >>> > > >>
> > > > > > > >>> > > >> I wasn't sure whether to start fleshing out a whole
> > > > > > AdminClient
> > > > > > > >>> API in
> > > > > > > >>> > > >> this
> > > > > > > >>> > > >> KIP (which would make it very big, and difficult to
> > > read),
> > > > > or
> > > > > > > >>> whether
> > > > > > > >>> > to
> > > > > > > >>> > > >> break it down into smaller KIPs (which makes it
> easier
> > > to
> > > > > read
> > > > > > > and
> > > > > > > >>> > > >> implement in pieces, but harder to get a high-level
> > > > picture
> > > > > of
> > > > > > > the
> > > > > > > >>> > > >> ultimate
> > > > > > > >>> > > >> destination). For now I've gone for a very small
> > initial
> > > > > KIP,
> > > > > > > but
> > > > > > > >>> I'm
> > > > > > > >>> > > >> happy
> > > > > > > >>> > > >> to sketch the bigger picture here if people are
> > > > interested.
> > > > > > > >>> > > >>
> > > > > > > >>> > > >> Cheers,
> > > > > > > >>> > > >>
> > > > > > > >>> > > >> Tom
> > > > > > > >>> > > >>
> > > > > > > >>> > > >
> > > > > > > >>> > > >
> > > > > > > >>> > >
> > > > > > > >>> >
> > > > > > > >>> >
> > > > > > > >>> > On 11 December 2017 at 21:31, Jun Rao <jun@confluent.io>
> > > > wrote:
> > > > > > > >>> >
> > > > > > > >>> > > Another question is on the compatibility. Since now
> there
> > > > are 2
> > > > > > > ways
> > > > > > > >>> of
> > > > > > > >>> > > specifying a partition reassignment, one under
> > > > > > > >>> /admin/reassign_partitions
> > > > > > > >>> > > and the other under /admin/reassignments, we probably
> > want
> > > to
> > > > > > > >>> prevent the
> > > > > > > >>> > > same topic being reassigned under both paths at the
> same
> > > > time?
> > > > > > > >>> > > Thanks,
> > > > > > > >>> > >
> > > > > > > >>> > > Jun
> > > > > > > >>> > >
> > > > > > > >>> > >
> > > > > > > >>> > >
> > > > > > > >>> > > On Fri, Dec 8, 2017 at 5:41 PM, Jun Rao <
> > jun@confluent.io>
> > > > > > wrote:
> > > > > > > >>> > >
> > > > > > > >>> > > > Hi, Tom,
> > > > > > > >>> > > >
> > > > > > > >>> > > > Thanks for the KIP. It definitely addresses one of
> the
> > > pain
> > > > > > > points
> > > > > > > >>> in
> > > > > > > >>> > > > partition reassignment. Another issue that it also
> > > > addresses
> > > > > is
> > > > > > > >>> the ZK
> > > > > > > >>> > > node
> > > > > > > >>> > > > size limit when writing the reassignment JSON.
> > > > > > > >>> > > >
> > > > > > > >>> > > > My only concern is that the KIP needs to create one
> > > watcher
> > > > > per
> > > > > > > >>> > > reassigned
> > > > > > > >>> > > > partition. This could add overhead in ZK and
> complexity
> > > for
> > > > > > > >>> debugging
> > > > > > > >>> > > when
> > > > > > > >>> > > > lots of partitions are being reassigned
> simultaneously.
> > > We
> > > > > > could
> > > > > > > >>> > > > potentially improve this by introducing a separate ZK
> > > path
> > > > > for
> > > > > > > >>> change
> > > > > > > >>> > > > notification as we do for configs. For example, every
> > > time
> > > > we
> > > > > > > >>> change
> > > > > > > >>> > the
> > > > > > > >>> > > > assignment for a set of partitions, we could further
> > > write
> > > > a
> > > > > > > >>> sequential
> > > > > > > >>> > > > node /admin/reassignment_changes/[change_x]. That
> way,
> > > the
> > > > > > > >>> controller
> > > > > > > >>> > > > only needs to watch the change path. Once a change is
> > > > > > triggered,
> > > > > > > >>> the
> > > > > > > >>> > > > controller can read everything under
> > > /admin/reassignments/.
> > > > > > > >>> > > >
> > > > > > > >>> > > > Jun
> > > > > > > >>> > > >
> > > > > > > >>> > > >
> > > > > > > >>> > > > On Wed, Dec 6, 2017 at 1:19 PM, Tom Bentley <
> > > > > > > t.j.bentley@gmail.com
> > > > > > > >>> >
> > > > > > > >>> > > wrote:
> > > > > > > >>> > > >
> > > > > > > >>> > > >> Hi,
> > > > > > > >>> > > >>
> > > > > > > >>> > > >> This is still very new, but I wanted some quick
> > feedback
> > > > on
> > > > > a
> > > > > > > >>> > > preliminary
> > > > > > > >>> > > >> KIP which could, I think, help with providing an
> > > > AdminClient
> > > > > > API
> > > > > > > >>> for
> > > > > > > >>> > > >> partition reassignment.
> > > > > > > >>> > > >>
> > > > > > > >>> > > >> https://cwiki.apache.org/
> > confluence/display/KAFKA/KIP-
> > > > 236%
> > > > > > > >>> > > >> 3A+Interruptible+Partition+Reassignment
> > > > > > > >>> > > >>
> > > > > > > >>> > > >> I wasn't sure whether to start fleshing out a whole
> > > > > > AdminClient
> > > > > > > >>> API in
> > > > > > > >>> > > >> this
> > > > > > > >>> > > >> KIP (which would make it very big, and difficult to
> > > read),
> > > > > or
> > > > > > > >>> whether
> > > > > > > >>> > to
> > > > > > > >>> > > >> break it down into smaller KIPs (which makes it
> easier
> > > to
> > > > > read
> > > > > > > and
> > > > > > > >>> > > >> implement in pieces, but harder to get a high-level
> > > > picture
> > > > > of
> > > > > > > the
> > > > > > > >>> > > >> ultimate
> > > > > > > >>> > > >> destination). For now I've gone for a very small
> > initial
> > > > > KIP,
> > > > > > > but
> > > > > > > >>> I'm
> > > > > > > >>> > > >> happy
> > > > > > > >>> > > >> to sketch the bigger picture here if people are
> > > > interested.
> > > > > > > >>> > > >>
> > > > > > > >>> > > >> Cheers,
> > > > > > > >>> > > >>
> > > > > > > >>> > > >> Tom
> > > > > > > >>> > > >>
> > > > > > > >>> > > >
> > > > > > > >>> > > >
> > > > > > > >>> > >
> > > > > > > >>> >
> > > > > > > >>>
> > > > > > > >>
> > > > > > > >>
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

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