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From Dmitriy Setrakyan <dsetrak...@apache.org>
Subject Re: A quick question on cluster topology and partitions?
Date Wed, 04 Jul 2018 02:05:29 GMT
On Mon, Jul 2, 2018 at 5:20 PM, John Wilson <sami.hailu.15@gmail.com> wrote:

> Regarding 1. I'm referring to the documentation here,
> https://apacheignite.readme.io/docs/topology-validation, which states
> "*Topology
> validator is used to verify that cluster topology is valid for further
> cache operations*." and "*If topology validator is not configured, then the
> cluster topology is always considered to be valid.*"
>

Yup. In this case, my answer is correct.


>
> Thanks,
>
> On Mon, Jul 2, 2018 at 4:21 PM, Dmitriy Setrakyan <dsetrakyan@apache.org>
> wrote:
>
> > On Mon, Jul 2, 2018 at 4:03 PM, John Wilson <sami.hailu.15@gmail.com>
> > wrote:
> >
> > > Hi,
> > >
> > >
> > >    1. What exactly is a cluster topology? What makes a cluster topology
> > >    invalid for further cache operations?
> > >
> >
> > Cluster topology is a set of Ignite nodes in the cluster. I do not think
> a
> > cluster topology could be invalid on its own. Perhaps you are asking
> about
> > a situation when after a certain number of node failures/stops we can be
> in
> > a situation where all primary and backup copies become inaccessible. In
> > that case, the cluster should enter a read-only state for the lost
> > partitions.
> >
> >
> > >    2.  Why do we have the concept of partitions in Ignite? Why don't we
> > >    have a key-to-node mapping rather than a key-to-partition and a
> > >    partition-to-node mapping?
> > >
> >
> > Main reason is because there is a finite number of partitions and there
> is
> > an infinite number of keys. Whenever ignite topology changes, Ignite must
> > rebalance data to the new nodes (or to the existing nodes). In this case,
> > Ignite needs to know when a certain partition is moved to another node.
> If
> > there were no partitions, then it would be impossible to tell when to
> > finish the rebalancing process.
> >
> > D.
> >
>

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