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From Sameer Kumar <sam.kum.w...@gmail.com>
Subject Re: Kafka Streams | Impact on rocksdb stores by Rebalancing
Date Tue, 09 Jan 2018 12:22:50 GMT
Got It. Thanks. Others can also take a look at
https://cwiki.apache.org/confluence/display/KAFKA/KIP-54+-+Sticky+Partition+Assignment+Strategy

-Sameer.

On Tue, Jan 9, 2018 at 5:33 PM, Damian Guy <damian.guy@gmail.com> wrote:

> Hi,
>
> yes partition assignment is aware of the standby replicas. It will try and
> assign tasks to the nodes that have the state for the task, but also will
> try and keep the assignment balanced.
> So the assignment will be more like your second assignment. If you are
> interested you can have a look at:
> https://github.com/apache/kafka/blob/trunk/streams/src/
> test/java/org/apache/kafka/streams/processor/internals/assignment/
> StickyTaskAssignorTest.java
>
>
> On Tue, 9 Jan 2018 at 11:44 Sameer Kumar <sam.kum.work@gmail.com> wrote:
>
> > Hi Damian,
> >
> > Thanks for your reply. I have some further ques.
> >
> > Would the partition assignment be aware of the standby replicas. What
> would
> > be the preference for task distribution: load balancing or stand by
> > replicas.
> >
> > For e.g
> >
> > N1
> > assigned partitions: 1,2
> > standby partitions: 5,6
> >
> > N2
> > assigned partitions: 3,4
> > standby partitions: 1,2
> >
> > N3
> > assigned partitions: 5,6
> > standby partitions: 3,4
> >
> > After N1 goes down, what would be the state of the cluster
> >
> > N2
> > assigned partitions: 3,4,1,2
> > standby partitions: 5,6
> >
> > N3
> > assigned partitions: 5,6
> > standby partitions: 3,4,1,2
> >
> > Or
> >
> > N2
> > assigned partitions: 3,4,1
> > standby partitions: 2,5,6
> >
> > N3
> > assigned partitions: 5,6,2
> > standby partitions: 1,3,4
> >
> > -Sameer.
> >
> > On Tue, Jan 9, 2018 at 2:27 PM, Damian Guy <damian.guy@gmail.com> wrote:
> >
> > > On Tue, 9 Jan 2018 at 07:42 Sameer Kumar <sam.kum.work@gmail.com>
> wrote:
> > >
> > > > Hi,
> > > >
> > > > I would like to understand how does rebalance affect state stores
> > > > migration. If I have a cluster of 3 nodes, and 1 goes down, the
> > > partitions
> > > > for node3 gets assigned to node1 and node2, does the rocksdb on
> > > node1/node2
> > > > also starts updating its store from changelog topic.
> > > >
> > > >
> > > Yes the stores will be migrated to node1 and node2 and they will be
> > > restored from the changelog topic
> > >
> > >
> > > > If yes, then what impact would this migration process have on
> querying.
> > > >
> > >
> > > You can't query the stores until they have all been restored and the
> > > rebalance ends.
> > >
> > > >
> > > > Also, if the state store restoration process takes time, how to make
> > sure
> > > > another rebalance doesn''t happen.
> > > >
> > > >
> > > If you don't lose any more nodes then another rebalance won't happen.
> If
> > > node1 comes back online, then there will be another rebalance, however
> > the
> > > time taken shouldn't be as long as it will already have most of the
> state
> > > locally, so it only needs to catch up with the remainder of the
> > changelog.
> > > Additionally, you should run with standby tasks. They are updated in
> the
> > > background and will mean that in the event of failure the other nodes
> > > should already have most of the state locally, so the restoration
> process
> > > won't take so long
> > >
> > >
> > > > -Sameer.
> > > >
> > >
> >
>

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